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55 Annual Report of China Institute of Atomic Energy 2005

Nuclear Physics

1 Nature of Chiral Candidate Bands in 134Pr*

CHEN Yong-shou, GAO Zao-chun

The chirality is common and has important consequence in science. Many biological and pharmaceutical molecules have static chirality when they are composed of four different atoms. The chirality may exist in nuclei when a particular angular momentum coupling scheme appears, where three angular momenta of the valence neutrons, the valence protons and the core are mutually perpendicular so that a left- and a right-handed system can be formed. 134Pr is a best candidate where the nearly degenerate doublet bands were found experimentally. However, the most crucial criteria for the chirality is the equivalence of the reduced E2 transition probabilities in the doublet bands. Very recently, the large difference of the experimental B(E2) values in the doublet bands of 134Pr has been reported[1]. Then a big question arises about the nature of the bands in 134Pr. To answer the question we carried out calculations of the electromagnetic transition probabilities and energy levels of the doublet bands with the triaxial projected shell model (TPSM) which has been developed recently in CIAE. The calculated band energies are compared with the experiment data in Fig.1, showing that a nice agreement between theory and experiment has been achieved. Particularly, the crossing behavior of the band 1 and the band 2 was reproduced by the calculation. At the nearly degenerate region, from I=14 to 18, the calculated B(E2) values are larger in band 1 than in band 2 by about a factor of 3 in average, reproducing the experimental B(E2) data quite well. The calculated results show also that from spin I=14 to 18 the doublet bands have completely different nature, the band 1 is a 2 quasiparticle (q.p.) band, 1n1p, while the band 2 is a 4 q.p. one, 1n3p. The shell model configuration mixing of the 4 q.p. components into the band 2 gives rise to the strong decrease of B(E2) values of the band 2 in the band interaction region of I=14-18. The chiral doublet bands must have similar intrinsic structure, therefore our theoretical results lead to a conclusion that the observed doublet bands in 134Pr can not be interpreted as the chiral bands.

Fig. 1 Calculated and experimental energy levels of the chiral candidate bands of 134Pr

■—Exp., band 1; ●—Exp., band 2;△—Theo., band 1; ▽—Theo., band 2

References:

FUNDAMENTAL AND APPLIED FUNDAMENTAL RESEARCH·Nuclear Physics 56

[1] TONEV D, et al. Phys Rev Lett, 2006, 96: 052501.

* Supported by National Natural Science Foundation of China (10305019, 10475115, 10435010) and Major State Basic Research Development

Program of China(G20000774)

2 Signature Inversion as a Probe for Triaxial Rotation*

CHEN Yong-shou, GAO Zao-chun

The signature inversion phenomenon has been widely observed in nuclear rotational spectra but has no common understanding for more that 20 years. The triaxial rotation is a fundamental question in nuclear structure. The present study attempts to achieve a thorough explanation for the signature inversion and to provide the rules to probe the rotation of triaxial nuclei by examining experimental signature inversion data. The signature is associated with the invariance of a system with intrinsic quadrupole deformation under a rotation of 180° around a principal axis, and is defined in the cranking model. We define the dynamic cranking axis as the axis along which the total angular momentum has a largest component. Note that the dynamic cranking axis can be any one of three principal axis of a rotating triaxial nucleus, while the cranking axis defined in the cranking model is a fixed one. We interpret the signature inversion as the change of the dynamic cranking axis in the rotational triaxial nuclear system. Take the yrast band of 157Ho as an example, where the twice signature inversions occur at spin I=39/2 and 51/2 respectively. This band is based on an intrinsic configuration of the deformation aligned orbital in the proton h11/2 shell, which has a large alignment Iy along the y-axis, the intermediate axis, thus the occurrence of the signature inversion in the band is determined by the character of the y-axis. The results of the present calculation show that the first signature inversion is caused by the change of the dynamic cranking axis from the y- to the x-axis, while the second inversion is due to the change back of the dynamic cranking axis to the y-axis from the x-axis (Fig. 1).

Fig. 1 Calculated expectation values of Ix2，Iy

2，Iz2with wave functions

that has reproduced the double signature inversions in Fig.2

■—Ix2；〇—Iy

2；△—Iz2


The cause of the change may be attributed to the alignments of the pair of neutrons in the i13/2 shell. The quantity S(I)=E(I)－E(I－1) for the yrast band of 157Ho was calculated with the triaxial deformed shell model which has recently been developed in CIAE. The calculated results well reproduce the double signature inversions observed in 157Ho, as shown in Fig. 2.

Fig. 2 Calculated energies E(I)－E(I－1) of yrast band states for 157Ho,

compared with the experimental data

Arrows indicate the signature reversion points

●—Exp.; 〇—Theo.

* Supported by National Natural Science Foundation of China(10305019,

10475115, 10435010) and Major State Basic Research Development Program of China(G20000774)

3 Signature Inversion: Manifestation of Driftof Rotational Axis in Triaxial Nuclei*

GAO Zao-chun, CHEN Yong-shou, SUN Yang1

(1 University of Notre Dame, Notre Dame, Indiana 46556, USA)

A possible scheme of realizing shell model calculations for heavy nuclei is based on a deformed basis and the projection technique. Here we present a new development, in which one starts with triaxially-deformed multi-quasi-particle configurations, builds the shell-model space through exact three-dimensional angular-momentum-projection, and diagonalizes a realistic two-body Hamiltonian in this space. The new model enables us to understand the old problem of signature inversion from a different view.

With an excellent reproduction of the experimental data in the mass 130 region(Fig. 1, Fig. 2), we interpret this phenomenon as a manifestation of dynamical drift of the rotational axis with presence of axial asymmetry in these nuclei. The neutron-proton interaction and the quadrupole-pairing force merely modify the detail but do not play an essential role in the underlying problem.


Fig. 1 Comparison of calculated energies with data for πh11/2νh11/2 band in 118-130Cs

Note the increasing trend in the reversion spin: 14.5 for 118Cs, 16.5 for 120Cs, 17.5 for 122Cs, 18.5 for 124Cs, 20.5 for 126Cs,

21.5 for 128Cs(prediction), and 22.5 for 130Cs(prediction)

●—Exp.; 〇—Theo.

Fig. 2 Calculated expectation values of Ix2, Iy

2 and Iz2 with wave functions

from diagonalization that has reproduced 124Cs data(Fig. 1)

■—Ix2；〇—Iy

2；△—Iz2

* Supported by National Natural Science Foundation of China(10305019,10475115,10435010) and Major State Basic Research Development



4 Beta Decay Theory Based on Projected Shell Model*

GAO Zao-chun, SUN Yang 1, CHEN Yong-shou (1 University of Notre Dame, Notre Dame, Indiana 46556, USA)

The wave functions calculated by the projected shell model have good angular momentums and good parities. This type of wave functions should describe, and indeed have successfully described many aspects of the nuclear properties. It is expected that good result could be obtained if one takes the PSM wave functions to calculate the beta decay matrix elements. Recently, this new beta decay theory, based on the projected shell model, has been formulated. As a testing example, we have calculated the Gamow-Teller(GT) transitions of 164Ho164Dy(Fig.1), and the calculated Logft values are in good agreement with experimental ones(Fig.2). It is predicted that those GT transitions without spin change are stronger than those with spin changed by one unit.

Fig. 1 Gamow-Teller transitions between excited states

●—Exp.; 〇—PSM

Fig. 2 B(GT) (a) and Log ft (b) of GT transitions shown in Fig.1

—Exp.; ★ ■—I→I－1; ●—I→I; ▲—I→I+1

* Supported by National Natural Science Foundation of China(10305019,10475115,10435010) and Major State Basic Research Development



5 Reflection Asymmetric Shell Model Description of Neutron-Rich 142Ba Nucleus*

CHEN Yong-Jing1, CHEN Yong-Shou, GAO Zao-Chun(1 Department of Physics, Tsinghua University, Beijing 100084, China)

The reflection asymmetric shell model (RASM) has been developed to describe the octupole deformed odd nuclei. With the RASM the calculated rotational bands have good angular momentum and good parity and then can be directly compared with the experimental rotational bands. In this report, we have applied this model to describe the octupole deformed bands of the neutron-rich even-even nucleus 142Ba. The quarupole-, octupole- and hexadecapole- deformation parameters used in this work are 0.127, 0.075 and －0.03 , respectively. The calculated results for the ground band and negative parity band of 142Ba are illustrated in Fig.1 and compared with the experimental spectra. From Fig.1 we can see that the calculation reproduces experimental data quite well. The experimental observation of the 1－ state has not been done, the predicted energy of the 1－ state is about 1.2 MeV above the ground state 0+, indicating the parity splitting is large. The octupole bands in 142Ba have the very interesting features, namely, the large parity splitting at low spins, the fast quenching of the parity splitting with increasing spin and the striking inversion of parity at around spin 9 beyond which the negative parity band becomes lower in energy than the positive parity band. All these features are reproduced by the present calculation, particularly, the parity inversion point Iinv = 9 is also well reproduced. The reason for the parity inversion has not yet been clear, and one possible explanation is due to the variation of the octupole correlation effect with increasing spin. The octuple correlation and its variation with spins are included in the RASM. However, more theoretical and experimental investigations must be carried out for a deep understanding about this phenomenon.

Fig. 1 Theoretical and experimental energies of the ground(solid circles) and negative parity(open circle) bands of 142Ba as a function of spin

Solid line, open line—RASM; ●, 〇—Experiment value


Program of China (G20000774)


6 Reflection Asymmetric Shell Model Description for 221,223Ra Nuclei*

CHEN Yong-jing1, CHEN Yong-shou, GAO Zao-chun(1 Department of Physics, Tsinghua University, Beijing 100084, China)

The octupole component of the mean field would influence single-particle orbits, and further, influence the band structure, and should be clearly manifested itself by the spectroscopy of odd-A nuclei, for example, the appearance of parity doublet bands. Because the spectroscopy properties of the odd-A nuclei have a direct and close relation with the single-particle orbits for which the intrinsic parities are violated, the study of the octupole deformed odd-A nuclei plays an important role in the study of the intrinsic reflection asymmetry in atomic nuclei. Reflection asymmetric shell model (RASM) is generated to describe octupole deformed odd-A nuclei. As a primary application of the theory, we have done calculations for typical octupole deformed odd-A nuclei, 221,223Ra. The calculated results reproduce quite well the experimental K=5/2 parity doublet bands in 221Ra and the K=3/2 doublet bands in 223Ra, the spins and parities of the ground states in the two nuclei are also reproduced correctly(Fig.1, Fig.2). It is shown that the RASM can well describe the octupole deformed odd-A nuclei, and thus the model will be an useful tool to explore into the nuclear reflection asymmetry.

Fig. 1 Comparison between calculated levels(th1 and th2) and experimental levels(exp1 and exp2) for 221Ra

Fig. 2 Comparison between calculated levels(th1 and th2) and experimental levels(exp1 and exp2) for 223Ra




7 Triaxial Superdeformed Bands in Doubly Odd 160-168Lu Isotopes*

Tuya, CHEN Yong-shou, SHEN Cai-wan1 , GAO Zao-chun(1 School of Science, Huzhou Teachers College, Huzhou 313000, China)

Since the first discovery of the triaxial superdeformation(TSD) band of 163Lu in 1992,a large number of bands with similar properties have been found experimentally in this mass region. They provide a unique possibility of studying superdeformed shapes with a pronounced triaxiality . In the present study, we systematically calculate the TSD bands in the doubly odd isotopes 160-168Lu by using the three dimensional Total Routhian Surface(TRS) model. The quadrupole, hexadecapole and triaxial deformations for the various configurations are calculated self-consistently. The present calculations predict about 10 low-lying TSD bands for each of these odd-odd Lu isotopes, and a lot of them have not been measured. As an example, the calculated TRS for the configuration πh11/2[514]9/2 － α=－ 1/2 vi13/2[642]5/2+α =1/2 in 162Lu are shown in Fig. 1.

From calculated TRS one can determines equilibrium deformations, (ε2,γ,ε4)= (0.457, 21.3° ,0.038).

Fig.1 TRS of 162Lu for the configuration πh11/2[514]9/2－α=－1/2vi13/2[642]5/2+α =1/2a—the counter plot of total routhian, "A" indicates a local TSD minimum with deformation ε2=0.457,γ=21.3°;

b— the counter plot of ε4, the hexadecapole deformation at symbol “+” is 0.038, which has the same position as “A” in (a)

We found in the doubly odd isotopes 160-168Lu for the selected low-lying configurations there exist many TSD shapes, indicating that the TSD shapes is a general phenomenon for the mass region . We also calculated the relative energy of the TSD band head to the ground state, this may be useful for the experimental searching for TSD bands. To investigate the formation mechanism of the TSD shape we analyze the calculated component energy surfaces in detail. It was found that the shell correction energy, especially neutron shell correction energy, plays a key role while the deformation-driving of the high- j orbital play an additional role in the formation of TSD band.

*Supported by National Natural Science Foundation of China (10305019, 10475115, 10435010, 10575036) and Major State Basic Research

Development Program of China(G20000774)


8 Isoscalar Giant Resonances of 120Sn in Quasiparticle RRPA*

CAO Li-gang1, MA Zhong-yu(1 Institute of High Energy Physics, Chinese Academy of Sciences)

Recently, Beaumel et al. have measured the inelastic scattering of 26Ne + 208Pb using a 60 MeV/u 26Ne secondary beam at RIKEN. This reaction is dominated by Coulomb excitations and selective for E1 transitions. The experimental data was under analysis when the paper was submitted. As a subsequent work, they will continue the experiment using a more neutron rich projectile 28Ne. Therefore, the theoretical investigation of low-lying dipole modes in 26Ne and 28Ne has a practical significance. The low-lying isovector dipole strengths in neutron rich nuclei 26Ne and 28Ne are investigated in the quasiparticle relativistic random phase approximation(Fig. 1).

26Ne and 28Ne are open shell neutron-rich nuclei. Recent investigations show that Z=16 for neutron-rich nuclei may form a new shell, which are populated in a spherical shape. Nuclear ground state properties are calculated in an extended relativistic mean-field theory plus BCS method where the contribution of the resonant continuum to pairing correlations is properly treated. Numerical calculations are tested in the case of isovector dipole and isoscalar quadrupole modes in the neutron rich nucleus 22O. It is found that in present calculation low-lying isovector dipole strengths at Ex < 10 MeV in nuclei 26Ne and 28Ne exhaust about 4.9 % and 5.8 % of the Thomas-Reiche-Kuhn dipole sum rule, respectively. The centroid energy of the low-lying dipole excitation is located at 8.3 MeV in 26Ne and 7.9 MeV in 28Ne.

Recently, the experiment data show that the low-lying dipole excitation energy is around 9 MeV and exhausts 5% of Thomas-Reiche-Kuhn dipole sum rule, which are in good agreement with our theoretical prediction.

Fig. 1 Isovector dipole strength function in 26Ne and 28Ne

a—26Ne; b—28Ne

Supported by National Natural Science Foundation of China (10305014, 90103020, 10275094) and Major State Basic Research Development



9 Effect of Pairing Correlation on Ground State and Collective Excitations of Nucleus*

CAO Li-gang1, MA Zhong-yu(1 Institute of High Energy Physics, Chinese Academy of Sciences)

The contribution of the resonant continuum to pairing correlations is properly treated in the relativistic mean-field (RMF) + BCS approximation with a constant pairing strength. The single particle resonant states in the continuum are calculated by imposing proper scattering bound conditions. Introducing a level density in the continuum we studied the effect of the widths of single particle resonant states on the ground state properties. It is found that the proper treatment of the resonance continuum is important to the exotic nuclei near the drip lines. It could affect the pairing gap, Fermi energy, pairing energy and the total binding energy of nucleus. The quasi-particle relativistic random phase approximation(QRRPA) is applied to investigate the collective excitations of open shell nuclei. The numerical calculations are performed in various isoscalar giant resonances in nucleus 120Sn. The contributions from the pairing are mainly at the low-lying excitation. Results show that the low-lying states can also be satisfactorily described in the QRRPA.

Supported by National Natural Science Foundation of China(10305014,90103020,10275094) and Major State Basic Research Development

Program in China(G2000077400)

10 Theoretical Study of 2H(d,γ)4He Reaction Below Ecm<3 MeV*

MA Yin-qun1, TIAN Yuan, MA Zhong-yu(1 Physics Department, Taiyuan Teachers College)

The reaction cross sections of 2H(d,γ)4He at the astrophysically interesting energies (about below few hundreds of keV) are extremely low. Presently it is impractical to measure in the laboratory. Therefore the theoretical investigation is required to predict the relevant cross section data. In this work we study the deuteron-deuteron radioactive capture reaction 2H(d,γ)4He at the incident energy Ecm<3 MeV and the astrophysical s-factor, which could well reproduce the experimental data. Then the astrophysical s-factor is extrapolated to the energy region Ecm<20 keV, where no experimental data are available. A direct capture method is adopted in the investigation of the 2H(d,γ)4He reaction that allows for the D-state component of the colliding deuterons. In the L-S coupling the system of d-d states have the following possible states with lowest angular momenta: 1S0，5S2，3P0,1,2,1D2. Considering electromagnetic radiation with multipolarity less than 2, the following transitions are allowed:<4He|E2|5S2>，<4He|E2|1D2> . Considering internal motion of the colliding deuterons, we make the following ansatz for the bound states and scattering states wave functions of the d-d systems,

(1)


)(sin)(cos 05

01 DS (2)

(3)

Here L is the orbital angular momentum, S the channel spin and J the total angular momentum, ФSd

the internal deuteron wave functions and f(R) a function of relative motion. The radial wave functions Ψα

are normalized to one. The mixing angular ω parameterizes the D-state amplitude in 4He. There are about 2%-17% uncertainty in the prediction of the 4He D-state probability with various theoretical models. The scattering wave functions Ψ are normalized to unit flux, where v and k are relative velocity and wave number of the colliding deuterons. We simply display our results for the capture cross section in the direct capture method:

（4）where Eγ=Ecm+23.847 MeV is the energy of the emitted photon, A(2S+1LJ) is the transition amplitude. At low energies it is most convenient to present the data in terms of the astrophysical S factor, defined by

S(Ecm)=σ(Ecm)Ecmexp(2πη) (5)where η=e2/ћv is the Sommerfeld parameter. We can well reproduce the energy dependence of the cross section if we choose ω=－0.275 leading to a 4He D-state probability of PD=7.4%. As is shown in Fig. 1, the theoretical results are in good agreement with the experimental data at Ecm<3 MeV. The uncertainty of the predicted 4He D-state probability can be attributed to many facts. One possible reason might be due to the p-wave contributions, which requires a further investigation.

Fig. 1 Reaction cross section σ(Ecm) of 2H(d,γ)4He as function of deuteron incident energy in center of mass

*Supported by National Natural Science Foundation of China (10305014,90103020,10275094) and Major State Basic Research Development

Program in China(G2000077400)


11 Isospin-Dependent Relativistic Microscopic Optical Potential*

RONG Jian, MA Zhong-yu

The Optical Model Potential(OMP) is one of the most powerful tools in the investigation of the nuclear reaction. In this work, the new decomposition of the Dirac Brueckner-Hartree-Fock(DBHF) G-matrix is adopted to investigate the isospin-dependent relativistic microscopic optical potential (RMOP). The optical potential of a nucleon in the nuclear medium is identified with the nucleon self-energy. The real part of the RMOP is evaluated in the DBHF approximation by adopting the decomposition of G=V+ΔG, and the imaginary part is constructed by the imaginary part of the second-order G-matrix exchange diagram. The optical potential for the finite nucleus is obtained by means of the local density approximation (LDA), where the space dependence of the RMOP is directly connected with the density and asymmetric parameter(β) of the asymmetric nuclear matter. The differential cross sections and the analyzing powers in the p+40Ca and p+208Pb at Ep less than 200 MeV are calculated with the RMOP. The isospin dependence of the RMOP is analyzed. Applying this RMOP, we also studied the nucleon elastic scattering off unstable nuclei and give some predictions on the proton-unstable nucleus scatterings.

The DBHF method adopts the realistic nucleon-nucleon (NN) interaction which is fitted to the NN scattering phase shifts and deuteron properties. The nucleon in-medium short-range correlation effect is taken into account in the DBHF by summing up all ladder diagrams. We adopt the new decomposition of the DBHF G-matrix, which was recently proposed by Schiller and Muether and calculate the Dirac structure of the nucleon self-energy. The G matrix is separated into a bare NN interaction V and short-range correction term ΔG. The projection method is only applied to the correction term, which is fitted by four pseudo-mesons. The ambiguities in the usual projection method are removed and a satisfactory description of the asymmetric nuclear matter (ASNM) and finite nucleus is achieved in this scheme.

The DBHF G-matrix contains the information of the isospin dependence of the effective interaction. The proton and neutron in various asymmetry parameters are distinguished in this work. Therefore, the RMOP obtained by the G-matrix is isospin dependent. It is found that the direct term is the dominant part in the nucleon self-energy, which is energy-independent. The exchange term produces an energy dependent quantum correlation to the nucleon self-energy, which contribution is smaller than that from the direct term. The contribution of the correlation term ΔG to the nucleon self-energies characterized by pseudo-meson exchanges is also energy independent due to the zero-range interactions adopted in this approach, and it reduces the intensity of the self-energies. At a fixed nucleon density β>0 corresponds to the neutron-rich nuclear matter. It is found that at low energies both scalar and vector potentials of the proton decrease as β increases. Interestingly, their energy dependence in the ASNM gets weaker than that in the symmetric one. Therefore, at certain energy the strengths of the scalar and vector potentials of proton become stronger than those in the symmetric nuclear matter(SNM), and vise versa for the neutron optical potential. The absolute values of the scalar and vector potentials of the neutron in the ASNM at low energies are larger than those in the SNM, and their energy dependence becomes stronger as β increases.

The DBHF calculation can not be directly extended to very low density region because the phase transition may occur. Therefore, the method of effective meson exchanges is introduced to study the RMOP in finite nuclei. We impose the condition that the nucleon self-energy and the binding energy per


nucleon at each density and asymmetric parameter obtained in the DBHF is reproduced by the four kinds of meson(σ, ω, δ and ρ) exchange in the RHF calculation. Then the coupling constants of the mesons can be determined by the fitting method. With the suitable approach, the coupling constants can be extrapolated to the lower density region.

Fig.1 Elastic scattering differential cross sections and analyzing powers in p+208Pb at Ep<200 MeV

Note that the differential cross sections are offset by powers of 10 (for Ep<100 MeV) and 100 (for Ep>100 MeV),

while the analyzing powers are shifted by increments of 2 (for Ep<50 MeV) and 3 (for Ep>50 MeV), respectively

With the effective meson exchanges and the LDA, the RMOP in finite nuclei can be obtained. We solve the Dirac equation in finite nuclei, by eliminating the small component of the nucleon Dirac spinor. Therefore, the Schroedinger type equation of the large component of Dirac spinors, as well as the Schroedinger equivalent potentials, the central and spin-orbit ones can be obtained automatically. The results show that the real part of the central potential is attractive at the low energy and becomes repulsive as the energy increases. At certain energy around 150 MeV or more an attractive pocket at the nuclear surface may occur, which is so-called “wine-bottle bottom” shape. It is formed by the balance between scalar and vector potentials. The intensity of imaginary central potentials increases as the energy


increases. These features are consistent with those observed in the phenomenological optical potentials.The differential cross sections and the analyzing powers in the p+40Ca and p+208Pb at Ep less than

200 MeV are calculated with the RMOP. The differential cross sections and the analyzing powers in the proton elastic scattering off 208Pb are plotted in Fig. 1. It is found that the calculated results coincide with the experimental results. It should be emphasized that the ROMP obtained from the DBHF G matrix without any free parameters could well describe the proton elastic scatterings off nuclei. The isospin dependence of the ROMP in finite nuclei is discussed and applied to unstable nuclei. We calculate the proton scattering off the Ca-isotopes and compare the results with and without distinguishing the proton and neutron densities. From the results of the Ca isotopes, it is found that the neutron skin or the halo structure in nuclei far from the β stability line may give large effects on the scattering observables. Therefore, the isospin dependence of the RMOP is important for exotic nuclei.

Supported by National Natural Science Foundation of China (10275094,10235020,10475116) and State Key Development Programme for Basic

Research of China (G1999022603,G2000077400)

12 Modified String Fragmentation Function and Particle Production in Nuclear Collisions at Top RHIC Energy

SA Ben-hao

A modified string fragmentation function is assumed in a hadron and string cascade model, LUCIAE (m), accounting for interactions among strings formed at the early stage of relativistic nucleus- nucleus collisions. It turns out that the experimental data of global properties such as the charged multiplicity and

the meson rapidity density at mid-rapidity in p+p, d+Au, and Au+Au collisions at =200 GeV are

well reproduced by LUCIAE(m) rather than LUCIAE(d) (default LUCIAE). However, LUCIAE(m) fails to account for the suppression of high pt transverse momentum spectrum observed in central Au+Au collisions at RHIC, even if final state rescatterings among produced hadrons are included in the calculations. The fact indicates that some novel mechanism has to be introduced to understand the suppression of hadron production at high pt.

13 Investigation in Possibility of Producing Superheavy FragmentsThrough Massive Nuclear Reactions at Low Energies

WU Xi-zhen, LI Zhu-xia, WANG Ning, TIAN Jun-long,ZHAO Kai, ZHANG Yin-xun, OU Li, LIU Min

In this paper, the possibility of producing superheavy fragments through composite system breaking up in massive nuclear reactions is investigated. Two main theoretical models, which are the quantum fluctuations within the fragmentation theory developed at 80 years and improved quantum molecular dynamics model developed recently by our group, are briefly reviewed. The dependence of the production probability of superheavy fragments on the incident energy, the decay mechanism of composite system


and superheavy fragments, and the distribution of binding energy of superheavy fragments are discussed for reactions of 244Pu+244Pu, 238U+238U, 197Au+197Au based on the improved quantum molecular dynamics model.

14 Dynamic Study of Fusion Reactions of 40,48Ca+90,96Zr*

ZHAO Kai, LI Zhu-xia, WU Xi-zhen, WANG Ning，ZHANG Ying-xun, TIAN Jun-long, ZHANG Huan-qiao, LIU Zu-hua

Based on the Improved Quantum Molecular Dynamics Model the fusion reactions of 40,48Ca+90,96Zr are studied by making a more rigorous treatment of the initial condition. The study shows us that: (1) the calculated fusion cross sections for all four reactions of 40,48Ca+90,96Zr are in good agreement with experiment data; (2) the sub-barrier fusion for the neutron-rich reaction 40Ca+96Zr is substantially enhanced compared with the other three reactions. In order to understand the reason why the sub-barrier fusion of neutron-rich reaction 40Ca+96Zr is enhanced compared with no neutron-rich reaction 40Ca+90Zr and the those of neutron-rich reactions 40Ca+90,96Zr are not enhanced, the further investigations are carried out, those are: the dynamic fusion barriers for four reactions, the relation between dynamic fusion barrier and nucleon transfer and the relation between nucleon transfer and corresponding reaction Q value. It has been found that positive Q value leads to the strong nucleon transfer which reduces the dynamic fusion barrier and enhances the sub-barrier fusion cross section.

* Supported by the National Natural Science Foundation of China (10235030,10235020,1017593,10175089)

15 Elliptic Flow and System Size Dependence of Transition Energies at Intermediate Energies*

ZHANG Ying-xun, LI Zhu-xia

One of the main goal for the research area of heavy ion collisions(HICs) at intermediate energies is to extract more accurate information of the nuclear equation of state(EoS). Considerable progress has been made recently in determining the equation of state of nuclear matter from heavy-ion reaction data. A prominent role among available observables is played by the collective flow. Many efforts on the study of the collective flow in HICs have been paid both experimentally and theoretically. The elliptic flow has proven to be one of the more fruitful probes for extracting the EoS and the dynamics of heavy ion collisions. The parameters of the elliptic flow is quantified by the second order Fourier coefficient from

the azimuthal distribution of detected particles at mid-rapidity as .

Positive values for v2 reflect a preferential in-plane emission, and negative values for v2 reflect a preferential out-of-plane emission.

The elliptic flow for Z≤2 particles in heavy ion collisions at energies from several tens to several hundreds MeV per nucleon is investigated by means of transport model, i.e. a new version of the


Improved Quantum Molecular Dynamics model (ImQMD05). In this model, a complete Skyrme potential energy density functional is employed. The influence of different effective interactions and medium corrections of nucleon-nucleon cross sections on the elliptic flow are studied. Our results show that a soft nuclear equation of state and incident energy dependent in-medium nucleon-nucleon cross sections are required for describing the excitation function of the elliptic flow at intermediate energies. The size dependence of transition energies for the elliptic flow at intermediate energies are also studied. The system size dependence of transition energies fits a power of system size with a exponent of 0.223.

* Supported by the National Natural Science Foundation of China (10175093, 10235030,10235020) and Major State Basic Research Development

Program in China (G20000774)

16 Re-visit N/Z Ratio of Free Nucleons From Collisions of Neutron-Rich Nuclei as a Probe of EoS of Asymmetric Nuclear Matter

LI Qing-feng1 , LI Zhu-xia(1 Frankfurt Institute fro Advanced Studies, Frankfurt University, Germany)

Following the establishment of radioactive beam facilities at many laboratories of different countries, the experimental studies on the equation of state (EoS) for asymmetric nuclear matter become possible. As is well known that the EoS for asymmetric nuclear matter is one of the most important input for astrophysics. There exist large uncertainties for the symmetry energy, especially, its density dependence. The symmetry energy at saturated normal density, i.e. the symmetry energy coefficient, is not well constrained. The theoretically predicted value are rather different from different approaches. In this paper we have studied the sensitivity of the N/Z ratio of free nucleons in collisions of neutron-rich nuclei at energies of 50 AMeV and 100 AMeV to the form of the density dependence of the symmetry potential energy term and the strength of the symmetry potential by using IQMD transport model. We have found that the N/Z ratio of free nucleons are sensitive to both the form of the density dependence of the symmetry potential and the strength of the symmetry potential term as well. The results of the influences of the different combinations of both symmetry potential strength and the form of the density dependence of symmetry potential show that the uncertainties of the symmetry energy coefficient largely reduce the sensitivity of the N/Z ratio of free nucleons from collisions of neutron-rich nuclei as a probe of the form of the density dependence of the symmetric energy part. It is urgently needed to have a more precise value of the asym in order to get more definite information of the density dependence of the symmetry energy.

17 Σ－∕ Σ+ Ratio as a Candidate for Probing Density Dependence

of Symmetry Potential at High Nuclear Densities

LI Qing-feng 1 , LI Zhu-xia (1 Frankfurt Institute fro Advanced Studies, Frankfurt University, Germany)

By using the UrQMD model we have investigated the influence of the symmetry potential on the


ratios between negative and positive charged pions and Σ hyperons in central collisions of 132Sn+132Sn and 112Sn+112Sn at energies 1.5, 2.5 and 3.5 AGeV. Two forms of the density dependence of the symmetry potential in the mean field are considered in order to find sensitive probes to the behavior of the symmetry potential at high-density nuclear matter. The obvious dynamical effect of the symmetry potential on neutron-rich reaction of 132Sn+132Sn is found and no effect on non-neutron-rich reaction system of 112Sn+112Sn is found. The effect of the symmetry potential on the π － /π+ ratio in 132Sn+132Sn at E=1.5 AGeV is similar to that found in paper (PRL 88,192701 (2002)) by Bao-An Li, but at higher energies like E=3.5 AGeV the effect disappears. It can be explained as at the E=1.5 AGeV case the most important channel for the production of pion is Δ decay while at the E=3.5 AGeV case the other channels also play an important role and the contribution from Δ decay ia largely reduced. The situation about the effect of the symmetry potential on Σ－∕Σ+ is more complicated because Σ hyperon itself also experiences a mean field of nuclear medium as soon as it is produced. When the symmetry potential of Σ hyporns is not taken into account, a similar behavior with that of π－/π+ ratio is found, i.e., the Σ－∕Σ+ ratio calculated with the soft symmetry potential is higher than that with the stiff one at E=1.5 AGeV and the sensitivity to the symmetry potential disappears at E=3.5 AGeV. As soon as the symmetry potential of Sigma hyperons is taken into account, the Σ－∕Σ+ ratio calculated with stiff symmetry potential becomes higher than that with soft one at E=1.5 AGeV and the Σ－∕Σ+ ratio calculated with soft symmetry potential is higher than that with stiff one at E=3.5 AGeV. This feature of the energy dependence of the relative values of the Σ－∕Σ+ ratio corresponding to different forms of the density dependence of the symmetry potential results from the dynamical effect of the symmetry potential of Σ hyperons. This feature may also be useful for us to extract the information of the symmetry potential of Σ hyperons in nuclear medium in addition to the structure of Σ hyper-nuclei.

18 Applications of Skyrme Energy-Density Functional to Fusion Reactionsfor Synthesis of Superheavy Nuclei

WANG Ning, WU Xi-zhen, LI Zhu-xia, LIU Min

The Skyrme energy-density functional approach has been extended to study the massive heavy ion fusion reactions. Based on the fusion barrier obtained and the parameterized barrier distribution the fusion (capture) excitation functions of a lot of heavy-ion fusion reactions are studied systematically. The average deviations of fusion cross sections of 92% systems in 76 fusion reactions with Z1Z2<1 200 from experimental data are less than 0.05 at energies near and above the barriers. For the massive fusion reactions, for example, the 238U-induced reactions and 48Ca+208Pb the capture excitation functions have been reproduced remarkable well. The influence of structure effects in reaction partners on the capture cross sections are studied and for qualitatively understanding the enhancement (excess neutron effect in neutron-rich nuclei) and suppression (closure shell effect) of capture cross sections at sub-barrier fusion energies the driving potential of the di-nuclear system model has been employed. Though comparing the fusion reactions induced by double magic nuclei 48Ca and by 32S and 35Cl, an optimal balance between the capture cross section of entrance channel and excitation energy of the formed compound nuclei are studied and the “threshold” of incident beam energy are explored. Finally, a lot of information on the fusion reactions with 36S, 37Cl, 48Ca and 50Ti bombarding on 248Cm, 247,249Bk, 250,252,254Cf and 252,254Es, and as well as the fusion reactions lead to the same compound nuclei with Z=120 and N=182 are provided, from


which one can obtain very useful information for study on unmeasured massive fusion reactions, especially for predicting the optimal fusion combination and suitable incident beam energy for synthesis of superheavy nuclei.

19 Dynamic Study on Damped Reactions of 244Pu+244Pu,238U+238U and 197Au+197Au

WANG Ning, LI Zhu-xia, WU Xi-zhen

In most attempts to produce superheavy elements(SHE), the complete fusion reactions have successfully been tried. Since the 70’s the elements from Z=107 to 116 were synthesized in the “cold fusion” reactions with lead and bismuth targets and “hot fusion” reactions with actinite targets. However, the further experimental extension of the region of SHE to the real ‘island’ with the complete fusion reaction is limited by the number of available projectiles and targets, and by the very low production cross section. In order to explore new more neutron-rich superheavy regions the radioactive ion beams will have to be utilized, but up to now the intensive radioactive ion beams are not available. In this case an alternative pathway to the superheavy elements, so called the strongly damped collision process between massive nuclei, for instance 238U+238U, would be worthwhile to be re-studied. The evident advantage of this kind of reactions would be the very large mass transfer probability and the high neutron-to-proton ratio which makes it possible to reach neutron-rich areas in the “island of stability” inaccessible to transfer or fusion reactions with lighter projectiles. In this letter, by using the microscopic transport model we study reactions of 244Pu+244Pu, 238U+238U and 197Au+197Au. We explore the dynamic process of the strong damped reaction and find that the production probability of superheavy products with Z larger than 114 in the 244Pu+244Pu reaction is much higher than that in the 238U+238U reaction, and for the 197Au+197Au reaction no products with Z larger than 114 has been found in the present study. The peak in the energy dependent production probability shows that the suitable selection of incident energy is very important for enhancing the probability of superheavy nuclei. The detail information about instantaneous structure and shape of superheavy products during the dynamic process has been obtained, which indicates that the exotic forms, for example , large deformed shape (band-like shape) could be one of stale configurations in superheavy nuclei.

20 Neutron Skin Thickness of Nuclei and Effective Nucleon-Nucleon Interactions

LIU Min, WANG Ning1, LI Zhu-xia, WU Xi-zhen(1 Institute for Theoretical Physics, Justus-Liebig-University Giessen, D-35392, Germany)

The Skyrme energy density functional is applied to study the ground state properties of nuclei and the stiffness of the symmetry energy. The binding energies and charge root-mean-square radii for selected nuclei can be described well. This makes us able to study the relation between the neutron skin thicknesses of nuclei and the isospin dependent part of the effective interactions. The figure shows the neutron skin thicknesses as a function of L (a) and Ksym (b) for 18O， 48Ca， 124Sn， 132Sn and 208Pb


calculated with 45 Skyrme interactions available up to now. and

give the slope and curvature of the symmetry energy near the saturated density,

respectively. The data obtained with various methods are also shown in Fig.1[1].

Fig.1 Data obtained with various methods

The dot curve gives the results of calculation;

The solid line gives the data for neutron skin thicknesses obtained with SDR2,

the dashed line gives those with antiprotonic atom method and the dash-dot line gives the results with (p,p) method

The calculation results show that the neutron skin thickness increase with the stiffness of the symmetry energy and the data obtained with antiprotonic atom method can be better described by more Skyrme interactions. Our study indicates that the model independent analysis method for extracting the neutron skin thickness is especially important for providing accurate information of the density dependence of the symmetry energy of nuclear matter.

Reference:[1] KRASNAHORKAY A, et al. Nucl Phys, 2004, A731: 224.

21 Applications of Skyrme Energy-Density Functionalto Fusion Reactions Spanning Fusion Barriers

LIU Min, WANG Ning, WU Xi-zhen, LI Zhu-xia


In this work, the Skyrme energy density functional has been applied to study heavy-ion fusion reactions. The properties of ground state nuclei are studied by using the restricted density variational method with the Skyrme energy density functional together with the semi-classical extended Thomas-Fermi approach (up to second order in ħ). With the proton and neutron density distributions obtained this way, the fusion barriers of a series of reaction systems are calculated by the same Skyrme energy density functional. We propose a parametrization for the weighing function based on the fusion barrier calculated with Skyrme energy density functional to calculate the fusion cross sections within the multi-dimensional barrier penetration theory. The weighing functions of the barrier are assumed to be two Gaussian functions. With the parametrization of the weighing function for multi-dimensional barrier, fusion excitation functions for more than 50 systems are calculated within the multi-dimensional barrier penetration theory. A large number of measured fusion excitation functions spanning the fusion barriers can be reproduced well. The competition between suppression and enhancement of sub-barrier fusion caused by neutron-shell-closure and excess neutron effects have been investigated.

22 Energy Dependence of Dynamic Barrierin Heavy-Ion Fusion Reactions

TIAN Jun-long, WU Xi-zhen, LI Zhu-xia

Based on the improved quantum molecular dynamics model, the incident energy dependence of dynamic potential barriers in the entrance channel of synthesis of heavier nuclei are investigated. It is found that the lowest dynamic barrier is obtained which approaches to the adiabatic static barrier with the incident energy decreasing and the dynamic barrier goes up to the diabatic static barrier with increase of the incident energy. A microscopic understanding of the extra-push of fusion reactions and a new explaining of tunneling process for the fusion at the incident energy below the static and above the lowest dynamic barrier is presented. In order to understand the energy dependence of the dynamical barrier we also pay a great attention to study the neck formation and shape deformation during the dynamic lowering of the barrier.

23 Application of Self-Consistent Collective Coordinate Methodto Multi-O(4) Model

GU Jian-zhong, Masato Kobayasi1, Kenichi Matsuyanagi1

(1 Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan)

Microscopic description of large amplitude collective motions in nuclei is a long-standing fundamental subject of nuclear structure physics. The self-consistent collective coordinate(SCC) method which was developed by a Japanese group in 1980s[1] is a promising theory for this subject. It deeply roots in the time-dependent Hartree-Fock theory and has a beautiful and compact mathematical formulation. The SCC method has been successfully applied to kinds of anharmonic vibrations and high spin rotations, mainly by Kenichi Matsuyanagi and his co-workers[2]. The successful application substantiated the SCC


method and illuminated its beauty and power.The SCC method allows us to derive a collective Hamiltonian which describes the collective motion

of a system. The collective Hamiltonian predicts the energy spectrum and transition strength of collective motion of the system. Being observable, the predicted ones can be tested by experimental data. The O(4) model captures the main features of nuclear forces and is suited to simulate the competition between the pairing of nucleons and deformation of nuclei. Based on the SCC method, we have derived the collective Hamiltonians for the single-shell O(4) model and for the multi-shell O(4) model in the spherical case. In the deformed case, the collective Hamiltonian for the multi-shell O(4) model was also calculated, which serves a starting point to study nuclear shape coexistence phenomena. We developed computer codes to calculate the spectra of the collective Hamiltonians and the quadrupole transition strengths among low-lying states. When the collective state vector evolves from a spherical point our results are consistent with those given by the exact solution of the multi-O(4) model.

We studied microscopically and self-consistently the nuclear shape coexistence phenomena by using the coupled-configuration SCC method suggested by Fukui [3]. The diabatic picture is used in this approach. Namely, one first, based on the SCC method, defines two diabatic configurations which correspond to the prolate and the oblate states, neglecting the couplings between them. The couplings between the two kinds of states are then treated in a manner similar to the well-known coupled channel method. We applied the coupled-configuration SCC method to the multi-shell O(4) model. We have calculated the couplings, low-lying states and transition strengths. They are in good agreement with the exact solutions, those given by the adibatic SCC[4] and those given by the generator coordinate method. In future we will apply the coupled configuration SCC method to a model with pairing-plus-quadrupole interactions, and finally to a model with realistic interactions. We shall pay our particular attention to the dynamical origin of the shape coexistence. This research will clarify the mechanism of the shape coexistence, then enrich and deepen our understanding of the shape coexistence.

References:[1] MARUMORI T, MASKAWA T, SAKATA F, et al. Prog Theor Phys, 1980,64:1 294.

[2] MATSUO M, MATSUYANAGI K. Prog Theor Phys, 1985,74:1 227.

[3] FUKUI Takahiro, MATSUO Masayuki, MATSUYANAGI Kenichi. Prog Theor Phys, 1991, 85:281.

[4] KOBAYASI M, NAKATSUKASA T, MATSUO M , et al. Prog Theor Phys, 2003, 110: 65.

24 Signature Splitting and Shape Coexistence in 127,129,131Nd

DONG Bao-guo

Signature splitting and shape coexistence at high spin in the neutron deficient nucleus 129Nd are investigated with the configuration-dependent cranked Nilsson-Strutinsky approach. The calculated bands are compared with the observed signature partner bands and very good agreement results at high spin are obtained. The observed deformed bands are confirmed as normal and highly deformed and their properties are explained theoretically. The calculated kinematic and dynamic moments of inertia J (1) and J (2) for configurations of interest are found to be generally in good agreement with the observed results. Terminating states in 129Nd and other terminations are predicted. There is shape coexistence within the same configuration from low spin to high spin states. Possible normal and highly deformed bands with


rotation around the intermediate principal axis in several interesting configurations of 129Nd are discussed. The experimental results for 131Nd are briefly discussed and the calculated bands are in good agreement with experimental observations at high spin. Experimental observable triaxial deformed bands with γ values of about －12° in 127Nd are predicted. The shape evolution of special configuration with neutron number increasing in 127,129,131Nd is discussed.

25 Statistical Properties of Resonance Matter in RHIC Reaction*

LU Zhong-dao, HU Shou-yang

In the relativistic heavy ion collisions a large amount of particles are produced, mostly they are particles in the resonant state and construct the resonance matter. The statistical properties, such as temperature, chemical potential (baryon chemical potential and strangeness chemical potential), net baryon density, total particle density, total energy density etc., can be described by quantum statistical theory. As the experimental data of the 200 AGeV RHIC (STAR data) available, adopted the least-square-method and combined the statistical theory with experimental data, we studied the properties of this reaction. The results from fitting the STAR data are as follows: the temperature of resonance matter is T=161 MeV，baryon chemical potential is μB =22.3 MeV，strangeness chemical potential is μS =4.77 MeV，net baryon density is 0.008 8 fm－3，total particle density is 0.42 fm－3（3 times of normal nuclear density） , total energy density is 0.41 GeV/fm3. This set of parameters and data clearly shows that the resonance particles at center rapidity region are produced with much higher energy than SPS energy but have experienced the expansion, the temperature decreasing and the dilution before measured.

* Support by National Science Foundation of China (10275096)

26 Unusual Threshold Anomaly in 6Li+208Pb System

ZHANG Huan-qiao, LIN Cheng-jian, ZHANG Chun-lei,RUAN Ming, LIU Zu-hua, YANG Feng, WU Xiu-kun

The angular distributions of elastic scattering for 6Li+208Pb system have been measured at several energies around the Coulomb barrier. The parameters of optical potential are extracted by means of a phenomenological optical model analysis. It is found that the real and imaginal potentials show a pronounced energy dependence. The behavior of the potential at the near- especially sub-barrier energies in the 6Li+208Pb system is quite different from the results of some previous reports observed in other systems, for example 19F+208Pb and 16O+208Pb. This unusual threshold phenomenon indicates that breakup channel is strongly coupled with the elastic channel and has obvious effects on optical potential.

This experiment was performed at HI-13 tandem accelerator of China Institute of Atomic Energy, Beijing. A 208Pb target of thickness about 150 mg/cm2 evaporated on a about 25 mg/cm2 carbon foil backing was bombarded by the collimated 6Li beam. Typical 6Li current range was 5-300 nA(electrical), because of the variety according to bombarding energy and scattering angle. An array of five ΔE-E silicon surface barrier detector telescopes was employed in the measurement, and 5 masks were placed in the


front of each telescope for the angular resolution. Two Au(Si) surface barrier detectors were used to monitor elastic scattering at 25° with respect to the beam direction for cross-section normalization, assuming that the elastic scattering cross sections equal to the Ruthford cross section at the forward angles.

The elastic scattering cross sections normalized to the Ruthford cross sections for some energies are shown in Fig. 1. The errors come from the statistic errors. For the forward angles the error is about 2% and about 10% for backward angles, however a few of errors at the backward angels especially when the energy is above the Coulomb barrier, are more than 10%, since the static is very low. Keeley et al. have extracted the 6Li+208Pb optical potentials from their measured elastic scattering angular distributions. In view of this data importance, we have measured the elastic scattering angular distribution with more beam energies 25, 27, 29, 31, 33, 35, 37, 41, 43, 46 MeV respectively.

Fig. 1 Elastic scattering cross sections normalized to the Ruthford cross sections

Our data analysis procedure is similar to that used by C. J. Lin et al. The phenomenological optical potentials are used in present work. The low-lying excited states and deformation of nuclei are not resolved, so the code PTOLEMY, a program for heavy-ion direct-reaction calculation is employed to fit the elastic scattering angular distributions to get the pure elastic scattering potentials.

There are 6 parameters to be determined in the optical potential. First, a grid search was done with VS

and WS as variables and other four parameters fixed (rv=r0w=r0, av=aw=a0). Here two sets of fit are finished with r0=1.24 and r0=1.30 fm. For each set, the influences of the potential parameters can be assessed with a0 ranging from 0.43 to 0.68 fm in step of 0.05 fm. An example of this is shown in Fig.2 for beam energy of 46 MeV. All the lines converge at a certain short distance, which is called sensitive radius RS and very close to the classical strong absorption radius D1/2. For different energies of the same system, the RS value is different, which indicates the RS depends on the energies and shows some differences between the real and imaginary parts of potentials, as listed in Table 1. For consistency, the average value of all the RSV

(RSW) of different energies, RS=12.4 fm are taken. Second, when r0=1.24 fm and a0=0.68 fm, the Χ's of the


fit reach the minimum values.The results are also listed in Table 1. The real and imaginary parts of potentials at the sensitive

radius(VS and WS ) are shown in Fig. 3b,d with square symbols. The errors are derived from the Χ2/pt values given by PTOLEMY. The results are very similar with corresponding results of N. Keeley for the same energy case. For comparison, the results obtained for the 19F+208Pb are also illustrated in Fig. 3a,c, which is the typical threshold anomaly.

In summary, the angular distributions of elastic scattering for 6Li+208Pb system are measured at ten energies around Coulomb barrier from 25 to 46 MeV. The parameters of optical potential have been extracted by the phenomenological optical model analysis. It is found that the optical potential shows the different TA behavior compared to the case of tightly-bound projectile. This unusual TA behavior indicates that the entrance(elastic) channel is strongly coupled with the breakup channel. In other words, breakup has obvious effects on elastic scattering process. The nuclei far from the stability-line, especially the halo nuclei, whose optical potential is an interesting problem, are usually weakly bound too. Besides the parameters of optical potential are the basic input parameters for the various calculations of other reactions. Therefore a better understanding of the breakup effects on the optical potential is of great importance for searching new phenomena in nuclear physics.

Fig. 2 V (r) and W (r) vs r for beam energy of 46 MeV

Fig. 3 Real and imaginary parts of potentials at the sensitive radius


a—19F+208Pb, reference; b—6Li+208Pb, this analysis; c—elastic scatterings, reference; d—elastic scatterings, this analysis

a, c—Rs=12.5 fm; b, d—Rs=12.4 fm

Table 1 Sensitive radii and results of best fits obtained at r0=1.24 and a0=0.68 fm for elastic scatteringELab/Mev RSV/fm RSW/fm －V0 －W0 Χ2/pt

46 12.56 11.55 12.0 26.2 6.51

43 12.25 11.44 13.0 22.0 22.30

41 11.92 10.94 9.5 23.4 2.04

37 12.57 11.68 12.8 27.0 18.50

35 13.55 12.34 20.2 32.1 9.70

33 12.95 12.08 28.1 28.5 16.20

31 12.98 13.09 21.4 29.6 8.12

29 13.21 13.00 16.3 32.9 10.40

27 12.63 13.27 15.2 41.1 8.49

25 12.21 11.51 18.9 50.7 16.27

27 Lifetimes Measurements of High Spin States in 178Os*

WU Xiaog-guang1, ZHU Li-hua1, CUI Xing-zhu1,2, LI Guang-sheng1, HE Chuang-ye1,LIU Ying1, WANG Shuo3, YU Ying-nan4, CHEN Yong-jing4, LI Li-hua1,WEN Shu-xian1, WANG Zhi-min1

(1 China Institute of Atomic Energy；2 College of Physics, Jilin University；3 Department of Physics, Peking University; 4 Department of Physics, Tsinghua University）

The present experiment was carried out at HI-13 tandem accelerator of the China Institute of Atomic Energy in Beijing. High spin states in 178Os were populated via 29Si+154Sm fusion evaporation reactions at beam energy of 155 MeV. The target was a 154Sm foil with a thickness of 1.4 mg/cm2, backed by a lead layer of about 20 mg/cm2 to stop the recoils. Gamma-gamma coincidence experiment was performed with an array consisting of fourteen Compton suppressed HPGe-BGO spectrometers. A total of 1.23108

coincidence events was accumulated on fixed disk in event by event mode. In the off-line analysis the event-by-event data were carefully gain-matched before they were stored into two dimensional E-E

matrices. The -ray coincidence relationships were established by setting gates on the photo peaks of individual transitions and background subtractions performed by Radware. Lifetimes of high spin states in 178Os are determined by analysing the Doppler-broadened line shapes.

The Doppler-broadened lineshapes were analyzed for the forward angle spectra and backward angle spectra. As an example, Fig.1 shows the observed and fitted lineshape for the 432 keV 8+6+ transition of the backward angle. the lifetime measurements of transitions performed by DSAMFT. The lifetimes of high spin states in 178Os are measured (Table 1) .

Table 1 Lifetimes of high spin states in 178Os

I π Eγ/keV τ /ps

8+ 432 2.37

10+ 488 2.14

12+ 538 0.198


14+ 585 0.139

16+ 625 0.119

Fig.1 Backward angle spectra of the 432 keV 8+6+ transition

The scatter is the experimental data, the solid is the a fit to the experimental lineshape

Support by National Natural Science Foundation of China (10175070) and Major State Basic Research Development Programme(G2000077405)

28 Structure of High Spin States in 52Mn*

WU Xiao-guang, ZHU Li-hua, HE Chuang-ye, WANG zhi-min, WEN Shu-xian,LI Guang-sheng, ZHANG Zhen-long1, MENG Rui1, CUI Xing-zhu1, MA Rui-gang, YANG Chun-xiang

(1 College of Physics, Jilin University, Changchun 130023, China)

The present experiment was carried out at HI-13 tandem accelerator of the China Institute of Atomic Energy in Beijing. High spin states in 52Mn, were populated via 12C+48Ti fusion evaporation reaction at beam energy of 55-85 MeV. The target was a 48Ti foil with a thickness of 1.5 mg/cm2, backed by a lead layer of about 20 mg/cm2 to stop the recoils. Gamma-gamma coincidence experiment was performed with an array consisting of fourteen Compton suppressed HPGe-BGO spectrometers. A total of 1.9108

coincidence events was accumulated on fixed disk in event by event mode. In the off-line analysis the event-by-event data were carefully gain-matched before they were sorted into two dimensional E-E

matrices. The -ray coincidence relationships were established by setting gates on the photo peaks of individual transitions and background subtractions performed using the packages of Radware, GASP ware and Specplot.

A new level scheme of 52Mn has been established from present experiment, as shown in Fig.1. In order to understand the insight structure of the high spin states of 52Mn observed in present work, we have performed semi-empirical shell model(SESM) calculations, shown in Fig.2. The calculation results were


in good agreement with the experimental results.

Fig.1 Partial level scheme of 52MnThe asterisk * indicate the new transitions observed in present experiment

Fig.2 New levels of 52Mn proposed from this experiment, compared with the results of SESM calculations

Support by National Natural Science Foundation of China(10105015, 10175070) and Major State Basic Research Development Program

(G2000077405)

29 High Spin Structures of Odd-Odd Nucleus 106Ag*


HE Chuang-Ye, ZHU Li-Hua, WU Xiao-Guang, WEN Shu-Xian, LI Guang-Sheng, WANG Zhi-Min, CUI Xing-Zhu1, ZHANG Zhen-Long1,MEI Rui1,MA Rui-Guang

(1 Department of Physics, Jilin University, Changchun 130023)

Chirality is recently observed in high spin states of triaxial nuclei. It is a new symmetry introduced to nuclear rotation. It has been suggested that chiral twin bands might be observed in the A~130, A~100 and A~180 transitional region[1]. The first experimental evidence for chirality structures, based on a πh11/2h11/2 configuration was reported recently in several N=75, N=73, N=71 isotones. Considerable effort has been made over the last two years to find chirality structures in A~100 mass region. Very recent work on 104Rh[2] has provided the experimental evidence for chirality based on the πg9/2h11/2

configuration. 106Ag[3] is the nearest N=59 isotones of 104Rh, it has great possibility to find chiral twin bands.

The high-spin states of 106Ag[3] were populated via the fusion-evaporation reaction 100Mo(11B, 5n)106Ag at a beam energy of 60 MeV. The 11B beam was delivered by the HI-13 tandem accelerator of the China Institute of Atomic Energy(CIAE). The target consisted of a 2.5 mg/cm 2 layer of 100Mo enriched to 97.4% and evaporated on an 11 mg/cm2 lead backing. A total of 130×106 γ-γ coincident events were collected in event-by-event mode. Fig. 1 shows the partial level scheme of 106Ag[3] deduced from the present work.

From Fig.1, it can seen that the levels of 106Ag are characterized by 4 rotational bands.1) The positive bandsIn the left side of the level scheme in Fig. 1, the 6+ state is a known isomer, be configuration of

π(g9/2)-3d5/2 coupled with the 100Sn core. Below the 12+ state, there are 2 bands with strong E2 transitions, in which the right band has M1 transitions between each levels, whereas the left one has M1 transitions only from the state of even spin to the state of odd spin. In former work [3], the right band is interpreted as a coupled band with configuration of πg9/2g7/2, and the left one is a semi-decoupled band with configuration of πg9/2d5/2. The levels above 12+ state are the members of the band built on the configuration of unpaired h11/2 neutrons. This band has much stronger M1 transitions than the E2 transitions, being possible magnetic band built on the configuration of unpaired h11/2 neutrons.


Fig. 1 Partial level scheme of 106Ag

Energies are in keV; γ transitions indicated by * are newly identified in present experiment 2) The negative bandsThe band (2) in Fig. 1 is a new band identified in our experiment, and its intensity is very weak. The

E2 transitions are much weaker than the M1 transitions in this band. For the assignment of Its configuration, a further analysis and theoretical calculations are needed.

The negative band (3) is the yrast band of 106Ag. It has stronger M1 transitions and weaker E2 transitions, its configuration is assigned as πg9/2h11/2

[3]. The yrare band (4) is similar as band (3), the energies of the levels between 13－ and 16－ are very close to that of band (3), especially for the 14－ state, the energy difference is only 39 keV. Comparing to the chiral bands observed in this mass region, we suggest that band (3) and band (4) are possible chiral twin bands of 106Ag.

The further analysis of above experimental data is under way.

References：[1] HECHT A A, BEAUSANG C W, AMRO H, et al. Phys Rev, 2003, C68: 054310.

[2] VAMAN C, FOSSAN D B, STAROSTA K, et al. Phys Rev Lett, 2004, 92: 032501.

[3] JERRESTAM D, KLAMRA W, GIZON J, et al. Nucl Phys, 1994, A577: 786.

* Supported by Major State Basic Research Development Program(TG2000077405) and National Natural Science Foundation of China (10175090,

10105015 and 10375092)

30 Optimal Reactions for Synthesis of Superheavy Nucleus 270Hs*

LIU Zu-hua, BAO Jing-dong1


(1 Physics department, Beijing Normal University, Beijing 100875, China)

The macroscopic-microscopic approach[1] predicts a strong proton-deformed shell at Z=108 to be a partner for the neutron shell at N=162. Thus the nucleus 270Hs is expected to be a relatively strongly bound “double-magic” deformed nucleus. Therefore, it is of great interest to synthesize the nucleus 270Hs and to investigate its structure experimentally. However, the cross sections of the superheavy nucleus formation are extremely small, in order of pb (10－ 12 barn). This feature makes the synthesis of the superheavy nucleus challenging. In order to successfully synthesize the superheavy nucleus it is very important to select the optimal combination of target and projectile, and the most favorable bombarding energy. In this report, we will present such optimal selections for synthesis of the superheavy nucleus 270Hs.

The system, originally in the fusion valley, is injected into the asymmetric fission valley after captured. The dynamics in the second stage is assumed to be described by a two-parameter Smoluchowski equation[2]:

(1)

Here x=s denotes the relative length between the effective surfaces of the approaching nuclei, and y=N represents the neutron number of the light nucleus. The potential, Vaf(x,y) in the asymmetric fission valley is calculated with the formulae in Ref. [3] and approximated by a repulsive parabolic potential Vaf(x,y)=－a(y)(x－xmax(y))2/2 with xmax(y) locating the maximum value in Vaf. By means of this potential, we get the drift coefficient Dx=a(y)(x－xmax )/αx. The drift coefficient Dx is proportional to the y-direction driving force evaluated with the potential governing the neutron flow[2].. In Eq. (1) we introduced a parameter γ to indicate the different time scales. In the limit γ>>1, which is consistent with the assumption that y will decays very rapidly to an equilibrium value yeq, Eq (1) can be reduced to a one-parameter Smoluchowski equation [2],

(2)

The operator L0,0 has the form

(3)

with

(4)

Here Φ0(y,x) is the eigenfunction of the operator Ly(y,x) for n=0.The solution of the Fokker-Plank Eq. (2) turns out to be a Gaussian. The probability to reach the

compound nucleus configuration is equal to the area under the distribution’s tail in the region x≤xmax [2]

(5)

where , and erfc is the error function complement, equal to (1－erf). is the average barrier

hight in the asymmetric fission valley.

The cross section of evaporation residue can be written as


(6)

The transmission probability is calculated using a “diffused-barrier formula”. The survival probability Wsur(E,J) is calculated with statistical model. Fig. 1 shows the evaporation residue cross sections for 4n channel for the reaction systems 30Si+244Pu, 36S+238U, and 48Ca+226Ra.

Fig. 1 Evaporation residue cross sections(σER)

for reactions 244Pu(30Si,4n)270Hs, 238U(36S,4n)270Hs, and 226Ra(48Ca,4n)270Hs

--- —30Si+244Pu; — —36S+248U; -·-·- —48Ca+226Ra

The superheavy nucleus 270Hs is expected to be a “double-magic” deformed nucleus. It is of great interest to synthesize the nucleus 270Hs experimentally. In order to successfully synthesize the superheavy nucleus 270Hs it is very important to select the optimal combination of target and projectile, and the most favorable bombarding energy. To this end, we have calculated its cross sections of evaporation residue for the reactions 244Pu(30Si,4n)270Hs, 238U(36S,4n)270Hs, and 226Ra(48Ca,4n)270Hs. It is found that the 226Ra(48Ca,4n)270Hs, and 238U(36S,4n)270Hs are two optimal reactions for the synthesis of the superheavy nucleus 270Hs due to their large negative Q-values.

References:[1] CWIOK S, PASHKEVICH V V, DUDEK J, et al. Nucl Phys, 1983, A410:254-270.

[2] LIU Z H, BAO J D. Chin Phys Lett, 2005, 12: 3 044-3 047.

[3] SWIATECKI W J, SIWEK-WILCZYNSKA K, WILCZYNSKI J. Phys Rev, 2005, C 71:014602-1-16.

* Supported by National Natural Science Foundation of China( 10235020,10235030)

31 Partial Fusion Induced by Weakly Bound Projectiles*

LIU Zu-hua, RUAN Ming, ZHANG Huan-qiao, YANG Feng, LIN Cheng-jian, WU Yue-wei

From theoretical point of view two different conflicting scenarios have been foreseen, one [1] predicts a fusion enhancement with respect to reactions involving stable nuclei, the other [2] predicts a fusion cross


section suppression due to the reaction flux lost in the breakup channel. Recently, Hagino et al. [3]

performed an improved coupled-channels calculation with the aim of reconciling the two conflicting scenarios. They predicted a complete fusion cross section enhancement at energies below the Coulomb barrier and a suppression at energies above the Coulomb barrier. These different theoretical predictions call for precise and reliable measurements as a watershed among various theories. The aim of the present work is to analyze the data for 6Li and 9Be pointing out the relation between partial and complete fusion at energies above the Coulomb barrier.

It is well known that fusion near and below the Coulomb barrier is strongly affected by the intric degrees of freedom of the interacting nuclei, whose coupling with the relative motion causes an energy splitting of the single uncoupled fusion barrier. This gives rise to a distribution of barrier heights, that manifests as an enhancement of fusion cross sections at energies near and below the Coulomb barrier. Above the Coulomb barrier this effect becomes less important and, at well above the Coulomb barrier, it can be neglected. Fusion cross section of tightly bound nuclei can be satisfactory described with the semi-classical approach formula

(1)

where VB (RB) is the barrier height (radius). We can rewrite Eq. (1) as

(2)

The （ E） /（ π ）= is called “reduced fusion cross section”. The is a linear

function of (E－VB). For weakly bound nuclei, the situation is more complicated. Coupling to channels that act as

doorways to breakup enhances the sub-barrier fusion cross sections, whereas breakup itself may result in capture of only a part of the projectile, thus suppressing complete fusion. These two effects may either partially or totally cancel at energies below the barrier. Above the Coulomb barrier, however, the breakup-capture and/or stripping-like process may manifest itself due to the disappearance of the coupling effects. We will therefore discuss the effect of breakup on fusion by comparing experimental complete fusion cross sections to Eq. (2).

In the case of tightly bound nuclei, the breakup probability is always assumed to be very small. Hence, the effect of breakup on fusion should be weak. This is the case for the well bound system 16O+208Pb that in the energy region above the barrier, follows rather well the straight line deduced from Eq.(2). Therefore, the 16O+208Pb system can be taken as a good reference for the discussion of breakup effects on fusion. While in the cases of weakly bound projectile induced reactions 6Li+208Pb, 6Li+209Bi and 9Be+208Pb, the complete fusion cross sections lie below the straight line defined by the Eq. (2) at the energies above the Coulomb barrier. Therefore, it is seen that complete fusion of weakly bound projectile with heavy target is suppressed.

In the fusion of weakly bound nuclei, two nuclei undergo a complete fusion(CF) and an incomplete or partial fusion(ICF) processes. The total fusion cross section is sum of CF and ICF cross sections. Fig. 1 shows the reduced cross sections of total (open symbols) and complete (solid symbols) fusion of the systems 6Li+209Bi and 9Be+208Pb with Eq. (2). It is shown that the reduced total fusion cross sections are in agreement with Eq. (2), which means the loss in the complete fusion are related with the partial fusion, i.e.,


2 Bπ 1BCF ICFV

RE

(3)

Fig. 1 Reduced fusion cross sections as a function of (E－VB)

for systems 6Li+209Bi, 9Be+208Pb, and 16O+208Pb

Recently, Diaz-Torres et al.[4] investigated the effect of breakup on total fusion using a new continuum discretized coupled channel(CDCC) method. They found that the breakup enhances the total fusion at energies just around the barrier, whereas it hardly affects the total fusion at energies well above the barrier. Thus their theoretical work supports our analysis.

References:[1] HUSSEIN M S, PATO M P, CANTO L F, et al. Phys Rev 1992, C46:377; 1993, 47:2 398

[2] DASSO C H, VITTURI A. Phys Rev, 1994, C50:R12.

[3] HAGINO K, VITTURI A, DASSO C H, et al. Phys Rev, 2000, C61:037602.

[4] DIAZ-TORRES A, THOMPSON I J, BECK C. Phys Rev, 2003, C68:044607.

* Supported by National Natural Science Foundation of China (10235030)

32 Primary Study on Radiation Effect of Biology Induced by Protons

ZHAO Kui, SUI Li, GUO Ji-yu, KONG Fu-quan, CAI Ming-hui, LIU Jian-cheng, YUE Mao-xing1, LIU Zhi-guo1, LI Jian-zhong1, XU Bing-xin1,

CHEN Ying2, LUO Qing-liang2, CHEN A-xin2, XIAO Min2, JING Hua2, HUA Nan2 (1 Special Medicine of Center of the 306th Hospital PLA, Beijing 100101; 2 Institute of Radiation Medicine, Beijing 100850 )

Radiation environment in outspace is a serious threat to astronauts for long duration space flight.


Galactic cosmic rays(GCR) and solar particle events(SPE) are the most important space radiation sources. Both the GCR and the SPE contain significant number of high-energy protons, capable of large penetration and important nuclear interaction. Those protons have high linear energy transfer and higher relative biological effectveness(RBE) comparing with the low LET radiation (such as electrons, X-rays and gamma-rays) and thus can induce more damage to biological specimen. Shielding method can not prevent all of radiation risk, radioprotector is essential require for astronauts.

In order to provide basic data for the radioprotector the protons accelerated by HI-13 tandem accelerator are used to simulate the space environment and the primary experiment about radiobiological effect induced by proton is performed. The protons of 19 MeV bombard the gold target of 1.3 mg/cm2, the scattering protons are defocus by Q3D spetrometor and then go through a Kapton foil of 50 m, the air of 1.5 cm and the plastic foil of 0.1 mm.. The energy of protons arriving to the surface of samples is 18 MeV. The LET is about 2.9 keV/m with range of 3.5 mm in water.

A Au-Si surface barrier semi-conduct detector is fixed at 35° in the target chamber for the fluency monitor of protons. The plasmid DNA, human blood, marrow of monkey and ICR mouse are irradiated by proton in the dose range of 0-30 Gy.

The primary experimental results are as follows. 1) There are no obvious changes in the AFM images of plasmid DNA up to 30 Gy proton radiation.2) The indexes of human blood are examined in the 7 days after proton radiation. The result show

that chromosomal aberration fractions of human peripheral blood cell are higher at dose of 0.5,1 and 3 Gy, then descend at 6 Gy and no chromosomal aberration are observed on dose of 10 Gy but vacuoles appear in the cells. That is a sign of cell apoptosis.

3) The cell cycle measurement indicates that serious G0/G1 arrest takes place in cells of monkey marrow after proton radiation.

4) 14 days after proton radiation survive percent measurements of mouse indicate that mousses survive 100% when they suffer from proton radiation of 4 and 8 Gy, survive 80% at dose of 16 Gy. When dose increase to 32 Gy, all of mouse died.

5) Besides the depilation and burning of skin, some mutations present to the skin cell as well as tissues of heart, liver, kidney and lung.

33 Study of DNA Sample for Atomic Force Microscopy*

CAI Ming-hui, ZHAO Kui, ZHAN Yong1, NI Mei-nan, SUI Li, KONG Fu-quan, YANG Ming-jian

(1 School of Science, Hebei University of Technology, Tianjin 300130, China)

Atomic Force Microscopy(AFM) was invented by Binnig，Calvin F. Quate and Christoph Gerber in 1986. AFM has unique advantages in observing biological sample. First of all, biological sample can be observed in physiological environment; Second, the force between AFM tip and sample is so little that biological sample can keep undamaged; Third, nonconductor also could be observed by AFM .Therefore, AFM had been used extensively in many fields after emergencing in 1986.

There is no doubt that the key point of using AFM is the preparation of the sample. At present, many ways of preparing DNA sample are used in different labs. Two methods of preparing DNA sample are used extensively in every labs. First, use bare mica as substrate, and add cations in DNA solution to


improve the absorbed force; Second, bare mica is treated with different reagents, such as cation, Glutaraldehyde, Spermidine and so on. However, there are many differences in preparing details. Such as, DNA concentration, cation concentration and absorbed time. In one word, different methods are suitable for different experimental aims. We must find new methods which are suitable for the length measurement of DNA and the fragments induced by radiation, as well as statistical analysis.

The bare mica is used as substrates in the new method. There are three steps in our experiment: First, adjust DNA concentration with a invariable Mg＋ concentration; Second, adjust Mg＋ concentration with a invariable DNA concentration which is selected in the first step; Third, adjust some details, such as, absorbed time and times of rinsing sample with water. By a great deal of experiments, DNA concentration and Mg＋ concentration are fixed on 1 ng/L and 1 mM, respectively.

Fig.1 AFM Image of DNA

Fig. 1 is the typical AFM image of PUC-19 plasmid DNA. The DNA sample is prepared with new method. The configuration of DNA can be clearly observed in the Fig.1, moreover the number of DNA molecular is moderate. With the new method of DNA sample preparation, we can measure the length of DNA molecular and the DNA fragments induced by radiation, and then make statistical analysis.

* Supported by National Natural Science Foundation of China (10175095, 10474018) and President Foundation of China Institute of Atomic Energy

34 DNA End-Joining Catalyzed by Cell-Free Extracts After Damaged by Heavy Ions

KONG Fu-quan, ZHAO Kui, ZHOU Ping-kun1, NI Mei-nan, SUI Li, CAI Ming-hui(1 Department of Radiation Toxicology, Institute of Radiation Medicine,

Academy of Military Medical Sciences, Beijing 100850, China)

It is ineluctability that the damage to astronaut will be induced by heavy ions along with the development to outer space. So the experiment of DNA end-joining catalyzed by cell-free extracts after DNA damaging by heavy ions is done.

The DNA sample is pGEM-T1 double-stranded plasmid DNA and is offered by department of radiation toxicology of Beijing Institute of Radiation Medicine, Academy of Military Medical Sciences. In the experiment, 19 MeV of 7Li (LET=120 keV/µm, in water) ions was generated by HI-13 tandem


accelerator at China Institute of Atomic Energy (CIAE), and the DNA samples in aqueous solution were irradiated with various doses (4, 6, and 8 Gy) in atmosphere at room temperature. After irradiating, DNA end-joining was catalyzed by cell-free extracts in vitro system. Fig.1 shows the result of agarose gels electrophoresis.

Fig.1 DNA end-joining after irradiated by heavy ions 7Li

a—Cell-free extracts is18.8 μg；b—Cell-free extracts is 63.45 μg

In Fig.1 a and b, M is marker, 4, 6 and 8 are DNA irradiated with 4, 6 and 8 Gy respectively. 4′, 6′and 8′are DNA that are end-joined after irradiating with doses of 4, 6 and 8 Gy respectively.

In agarose gels electrophoresis, the supercoiled DNA moves more quickly than the linear form DNA because the supercoiled DNA is compact. In Fig. 1, the dimer form DNA like the experiment of PETER Baumann et al.[1] do not appear. But the fraction of linear form DNA increases after catalyzing by cell-free extract contrast to that before catalyzing. This phenomenon is more evident in the dose of 6 Gy than that in other doses. The reaction system Fig.1b has more cell-free extracts than the reaction Fig.1a. So it is evident that the increasing of linear form DNA in reaction system Fig. 1b is stronger than that in reaction system Fig. 1a. It may be that there are some damages of bases and sugar-bases in the DNA that still keep up the supercoiled form after irradiating. In the cell-free extracts, there may have some enzymes that can distinguish these damages and cut out them. Thus the supercoiled DNA turns into linear form DNA. The dimer and trimer do not appear in the experiment. The reason may be that two ends of linear DNA induced by heavy ions are not as regular as in the case of enzyme cut. All of these need more work.

Reference:[1] PETER B, STEPHEN C W. DNA end-joining catalyzed by human cell-free extracts.Biochemistry, 1998, 95:14 066- 14

070.

* Supported by National Natural Science Foundation of China( 10175095, 10435020) and President Foundation of China Institute of Atomic Energy

35 Study on Double-Strand Break of DNA Irradiated by γ Rays*

KONG Fu-quan, ZHAO Kui, SUI Li, CAI Ming-hui, YANG Ming-jian

DNA is considered to be the most important bio-macromolecule and target molecule responsible for all biological effects. Many kinds of damage can be induced by radiation, such as base damage, single strand break(SSB), double strand break(DSB) and crosslink of DNA and protein. DNA double strand breaks(DSBs) are considered to be the most important initial damage of all biological effects induced by


high-LET heavy ions radiation. In particular, unrejoined DSBs are responsible for cell death. In order to evaluate the relative biological effect(RBE) of DNA damage induced heavy ions,double-

stranded pUC19 plasmid DNA is irradiated by γ rays. The pUC19 is purchased from TaKaRa Biotechnology (Dalian) C., Ltd. at a concentration of 500 ng/μL in TE buffer (10 mM Tris-HCl (pH 8.0),1 mM EDTA). The plasmid is 2686 bp long. Before irradiation, the plasmid DNA was diluted to 250 ng/μL and 100 ng/μL. The free radical scavenger mannitol is added to the plasmid DNA at a concentration of 100 ng/μL. The samples are irradiated on ice in the course of irradiation with doses of 300, 500 and 700 Gy for 1 hour. After irradiation, the samples are analyzed by electrophoresis through 1% agarose gels for 40 min followed by photographic system.

Fig. 1 Electrophoresis photograph of DNA after irradiated by γ rays

In Fig.1, lanes 1, 2 and 3 are the DNA irradiated with dose of 300 Gy. Lanes 4, 5 and 6 are the DNA irradiated with dose of 500 Gy. Lanes 7, 8 and 9 are the DNA irradiated with dose of 700 Gy. Lanes 1, 4 and 7 show the DNA irradiated at a concentration of 250 ng/μL. Lanes 2, 3, 5, 6, 8 and 9 show the DNA irradiated at a concentration of 100 ng/μL. At the same time, the DNA in lanes 3, 6 and 9 are added mannitol at concentrations of 400 mM, 600 mM and 200 mM respectively.

It is shown that there are only two forms (linear and open circular DNA) in the lanes 1, 2，4，5，7 and 8. And a shift to the fraction of the linear DNA is observed with the increasing dose. It indicates that DNA is damaged more and more seriously with the increasing dose. Compared with lanes 1, 4 and 7, the fraction of linear DNA in lanes 2,5 and 8 increases. It shows that DNA at a lower concentration can be damaged easier at the same dose. In all the lanes, only lanes 3, 6 and 9 have more supercoiled DNA and not linear DNA. It indicates that the mannitol has a function of scavenging free radical and protecting DNA when DNA is irradiated. So the dose, concentration of DNA and mannitol all influences the double-strand breaks of DNA induced by γ rays.

* Supported by National Natural Science Foundation of China (10175095,10435020) and President Foundation of China Institute of Atomic Energy

36 Investigation of pUC19 DNA Damage Induced by Direct andIndirect Effect of 7Li Ion Radiation

SUI Li, ZHAO Kui, NI Mei-nan, GUO Ji-yu, KONG Fu-quan, CAI Ming-hui1, YANG Ming-jian1, LIU Jian-cheng


(1 Hebei University of Technology, Tianjin 30013)

Numerous DNA lesions，such as base damage, single- and double- strand breaks(SSBs and DSBs), and cross-linking induced by direct and indirect effect(free radical) of ionizing radiation. DNA DSBs are considered as the most important initial damage of all biological effects induced by radiation. Free radical produced by radiation may be the main factor of yielding SSBs and DSBs in aqueous solution. It is essential to study the dynamics of free radical reaction by establishing proper in vitro model systems. In this experiment, we investigate the reactive dynamics of DNA strand breaks induced by heavy ions with atomic force microscopy (AFM).

Using 19 MeV of 7Li heavy ion (LET=120 keV/μm, in aqueous solution) generated by HI-13 tandem accelerator, three conditions of pUC19 plasmid DNA samples including aquiform, dry and adding various concentrations radical scavenger(mannitol) are irradiated at different doses from 10 to 1 000 Gy in air. After irradiating, these DNA samples are analyzed with AFM in nanometer-scale. There is the change of three forms of DNA, supercoiled (intact DNA), open circular (OC, DNA with SSB) and linear form (L, DNA with DSB), as the dose is observed. Results obtained as follows.

1) For the aquiform DNA, the forms of DNA show regular change from SC to OC or L as the dose increases. At a dose of 1 000 Gy, nearly 90% of the DNA molecules are in long or short linear fragments.

2) For the dry DNA, the fraction of OC form increases with increasing dose and is larger than that for the aquiform DNA under the dose of 700 Gy. But the fraction of L form shows irregular change as the dose increases, and far lower than that for the aquiform DNA. These imply that DNA SSBs and DSBs induced by 7Li ion as the result of direct and indirect effect, and the direct effect may be the main reason for yielding SSBs in dry DNA, the indirect effect may be the main factor of yielding DSBs in aqueous solution. Furthermore, DNA-DNA cross-linking is observed in irradiated dry DNA, which competes with DNA strand breaks. This may be a reason of lower yield of DSBs in dry DNA.

3) For the adding various concentrations mannitol DNA, we observe the stronger protection effect of mannitol for DNA molecules at a dose of 1 000 Gy. As the concentrations of mannitol increase, the fraction of SC form increases, but the fraction of L form is lost gradually. At the 400 mM of concentration, the percent of L form is only 5%. These indicate that mannitol can effectively scavenge free radical and reduce the yields of SSB and DSB. These results also reveal that free radical is the important factor in 7Li ion radiation induced DNA SSBs and DSBs under condition of aqueous solution.

In order to compare the effect of direct and indirect in heavy ion radiation with γ-rays radiation, three conditions of pUC19 plasmid DNA samples irradiated by 60Co γ-rays at various doses from 500 to 2 000 Gy. The result analyzed with AFM shows that γ-rays more severely induce DNA strand breaks in

condition of aqueous solution compared with dry. That is to say free radical may be the main factor in γ-

rays radiation induced DNA damage. Though the dose is 30 and 2 000 Gy respectively, the fraction of three forms of dry DNA after 7Li ion and γ-rays irradiation is the same. This indicates that direct effect is important in 7Li ion radiation induced DNA damage. In addition, the stronger capability of mannitol protecting DNA is observed in γ-rays radiation.

Above results are important to further study the reactive dynamics of DNA strand breaks induced by heavy ions in the future.

37 Indirect Measurement of Cross Section of 9Be(p,α)6Li


LI Cheng-bo, WEN Qun-gang, MENG Qiu-ying, ZHOU Jing, HU Shou-yang,FU Yuan-yong, LI Xiao-mei, ZHOU Shu-hua, YUAN Jian, LI Xia, LIN Cheng-jian, XU Guo-ji

The cross section of 9Be(p,α)6Li at low energies is important for nuclear astrophysics. But it is difficult for direct measurement because of the Coulomb barrier and electron screening effect. In order to measure the 9Be(p,α)6Li bare nucleus cross section at astrophysical energies, the Trojan Horse Method(THM) can be applied. The main feature of the method is that it allows to extract the energy dependence for the bare astrophysical S(E) factor at very low energies without any extrapolation, by measuring the cross section of an appropriate three body process.

In our experiment, the 9Be(p,α)6Li reaction is studied by means of the THM applied to the 2H(9Be,α6Li)n. In this case, the deuteron is used as “Trojan Horse” nucleus, having a high probability to be described as d=(p+n), in this framework the proton acts as the participant and the neutron as a spectator to the virtual two-body process 9Be(p,α)6Li. The quasi-free reaction process is shown as Fig. 1.

The experiment has been carried out at HI-13 tandem accelerator in CIAE. A 9Be2+ beam of energy at E=22.44 MeV and intensities up to 1-5 pnA impinged on a CD2 linear foil target of about 257 μg/cm2

thick and 1.5 mm wide. Two position sensitive detectors(PSD) which can give both precise energy and position signals are used for detecting α and 6Li in coincidences. The PSDs are placed at the so-called quasi-free angular pairs (PSD1: 12.45°-23.44°，to detect α；PSD2: 4.53°-15.43°，to detect 6Li), where the quasi-free process contribution should be mostly present. Signals are sent to Kmax data acquisition system via electronics.

Figure 2 is the experimental spectrum of E1-E2 from 2H(9Be,α6Li)n reaction. The energy dependence of the two body reaction cross section of 9Be(p,α)6Li at low energy range can be extracted from the 2H(9Be,α6Li)n reaction data via THM theory. The data analysis is under processing.

Fig.1 Sketch map of quasi-free process


Fig.2 Experimental 2D-spectrum of E1-E2 from 2H(9Be,α6Li)n reaction

38 Identification of SEU Sensitive Region of CMOS SRAM Using Heavy Ion Microbeam*

GUO Gang, HUI Ning, CHEN Quan, SHEN Dong-jun, XU Jin-cheng,HE Chao-hui 1, GUO Hong-xia 1, LI Yong-hong 1, LUO Yin-hong 1,

YAO Zhi-bin 1, ZHANG Feng-qi 1, SU Xiu-di 2, LI Wei 2

(1 Northwest Institute of Nuclear Technology；2 Northeast Microelectronics Institute)

A 2K-bit static random access memory (SRAM) was irradiated using 79Br ion beam with energy of 145 MeV at heavy-ion microbeam facility which connected with HI-13 tandem accelerator at China Institute of Atomic Energy(CIAE). The beam spot of the microbeam was estimated to be around 2.5 m3.5 m. The single-event upset (SEU) sensitive regions and the areas of the SRAM cell irradiated were identified using SEU mapping technique.

As shown in Fig. 1 is the microscope image of SRAM cells. Experiment results are shown in Fig. 2. The number 55 was written into the memory by a SEU tester before each run of irradiation. The SEU-sensitive regions are the reversed-biased NMOS and PMOS drain which are in the “off”-state. Measuring the areas of the SEU-sensitive region gives (58±32) m2 for NMOS, (14±10) m2 for PMOS, and a total cross-section of (71±34) m2 per cell.


Fig. 1 Microscope image of SRAM cell

Fig. 2 SEU-image of a 2K-bit CMOS SRAM

* Supported by National Science foundation of China(10375097) and Nuclear Industry Foundation of China(4160205030503)

39 Neutron- Emission Competition in Spontaneous Fission of 252Cf*


HAN Hong-yin, XIA Hai-hong, WANG Tao-feng, MENG Qing-hua1,ZHU Li-ping, WANG Li-ming, HOU Long

(1 Northwest Institute of Nuclear Technology）

Nuclear fission is a process in which two fragments with the large deformations are formed at the scission. Because of excitation of bending and wriggling modes at scission as well as Coulomb torque between two fragments after scission, these closely related mechanisms result in the initial fragment angular momenta appearing in the fragments. As the fragments collapse to their equilibrium shape, the internal excitation energy stored in fragments before the scission and the excitation energy converted by the fragment deformation after the scission may be to dissipated by neutron emission, and the residual energy after neutron emission is expected to appear as -ray emission because the neutron emission is hindered by an angular momentum barrier of fragments. So the neutron multiplicity and the -ray multiplicity are relative directly to the fragment excitation energy and the initial fragment angular momenta, respectively. According to the positive correlation between the average neutron yield ν and the average -ray multiplicity M, observed for the spontaneous fission of 252Cf(sf), the empirical formula M=1.13ν+3.0 is suggested[1]. It must be noted that the recent measurements [2] show that the above description may be incorrect. In this work variations of both average neutron yield ν(A*) and average -ray multiplicity M(A*) with initial individual fragment mass A* were measured for 252Cf(sf) reaction. The data acquisition was completed using a four-parameter correlation measurement.

The fission source with a spot in diameter of 5 mm and an activity of about fissions per second, prepared on the carbon backing with a thickness of 40 g/cm2, was mounted between two semiconductors (F1 and F2) face-to-face. Both fission detectors ( mm) were collimated down to 16 mm in diameter. The fission source and the fission detectors (F1 and F2) were positioned in a small chamber ( cm cm) with a wall thickness of 1 mm and at a high vacuum of about 0.2 Pa. A liquid scintillator (1 cm cm) behind the F1, mounted at a distance of 46 cm from the F1, was served as neutron detector; while a HPGe detector behind the F2, with efficiency 60% for the -ray detection, was placed at 36 cm distance from the detector F2. The distances from the fission source to the F1 and the F2 were 6 cm and 4 cm, respectively. All detectors (F1, F2, liquid scintillator, HPGe) and the fission source are mounted coaxially. To determine the absolute values for ν(A*)and M(A*) in the range of fragment mass number from A*=85 to 167, the kinematical focus effect of neutron emission from moving fragments and the Doppler shift effect of -rays from the moving emission source were employed. A total of about 5 correlation events were analyzed.

For convenience the experimental results are given by the correlation function M(ν). The experimental results are the followings. 1) In the case of fragments at A*=85 to 123 amu, M is a very weak linear increasing function of ν, namely as ν varies from 0.4 to 3.2 the M increases linearly from about 4.1 to about 4.8; 2) There exists a strong positive correlation between M and ν for the near symmetric fragments with mass A*=124 to 131, that is to say, M increases from about 2.0 to about 4.2 with increasing ν from 0.45 to about 3.2; 3) The a strong complex correlation, observed for the asymmetric heavy fragments in the range from A*=132 to 167, is shown in Fig.1.

All the experimental facts above mentioned, especially the data given in Fig.1, indicate unambiguously that the simple positive correlation description of neutron- emission competition is incorrect; in other words, the experimental data shows strongly that the neutron- emission competition is complex in the spontaneous fission of 252Cf. It must be pointed out that this complex correlation between neutron emission and -ray emission is difficult to be explained only on the basis of excitation mechanism

Fig.1 M as a function of for A*=132167


of bending mode at scission or Coulomb torque after scission. The higher ν(A*), the more distorted is the fragment; and the more distorted the fragment, the more rotational angular momentum, namely the larger -ray multiplicity M . In order to explain various gamma emission data including the n- complitition measured in this work, it is essential to develop a new theoretical model for the angular momentum excitation in fragments, although a new mechanism of fragment de-excitation, that is to say, the orientation pumping mechanism of fission -ray emission, has been suggested recently.

Fig. 1 M as a function of ν for A*=132 to 167

References:[1] NIFENECKER H A, SIGNARBIEUX C, et al. Nucl Phys, 1972, A189:285.

[2] MIKHAILO I N, QUENTIN P. Proceedings of the Second Int. Conf. On Fission and Properties of Neutron-Rich

Nuclei. Scotland, 1999: 384.

* Supported by National Natural Science Foundation of China(10175091)

40 Production of 10C Secondary Beam

SU Jun, LI Zhi-hong, LIAN Gang, WANG You-bao, GUO Bing, ZENG Sheng, YAN Sheng-quan, WANG Bao-xiang, BAI Xi-xiang, LIU Wei-ping

The inhomogeneous big bang models assume a universe with regions of high-density proton-rich materials surrounded by those of low-density neutron-rich materials, thus many reactions caused by unstable nuclei are very important. Fig. 1 shows a part of the nuclear reaction network of primordial nucleosynthesis[1]. The reactions related to 10C are considerable in the investigation of primordial nucleosynthesis. The nuclei close to the driplines are mainly produced through complicated reactions between stable nuclei, while, the driplines can be approached in simple reactions involving radioactive nuclei, for example, the 10C+p elastic resonance scattering can be used to study the unbound nucleus 11N[2,3]. Furthermore, the measurement of the strength of the superallowed 0+→0+ transition in the β-decay of 10C is important for checking the conserved vector current hypothesis[4,5].


Fig. 1 Part of the nuclear reaction network of primordial nucleosynthesis

The experiment was carried out using the secondary beam facility [6] of HI-13 tandem accelerator. A 72 MeV 10B primary beam impinged on a hydrogen gas cell at a pressure of 1.6 atm, produced 10C secondary beam through the 1H(10B,10C)n reaction in inverse kinematics. The front and rear windows of the gas cell are Havar foils, each with a thickness of 1.9 mg/cm2. The 10C ions were separated from other series by a dipole magnet. The magnetic rigidity of ion can be expressed as

(1)

In the equation, Bρ, q, M and EK denote the magnetic rigidity, charge state, mass and kinetic energy of ion, respectively. The strength of the magnetic field was set to match the magnetic rigidity of 10C6+. The other ions can be effectively separated since their energies are observably higher than those matching the magnetic rigidity of 10C6+, however, their low energy tails can match the magnetic rigidity.

To enhance the purity of the secondary beam, a wien filter had been installed on the downstream of the beam line. The force of the ion with the velocity of from the electric ( ) and magnetic ( ) fields in the wien filter is given by

(2)where β=ν/c，c is the velocity of light. Two apertures with the diameter of 3 mm and 5 mm had been set up in front of the secondary charge. The strength of the electric and magnetic fields were set to match the velocity of the 10C6+. The deflected distance of the impurity before secondary charge are far bigger than the diameter of the apertures, thus the widen filter can effectively enhance the purity of the 10C beam. The secondary beam was detected and identified with a ΔE-E counter telescope consisting of a 19.3 m silicon ΔE and a 300 m silicon E detector.

The two dimension spectrum of ΔE-Et is shown in Fig.2. The purity of the collimated 10C beam was about 92 % after the magnetic and velocity selection, the beam energy was (55.9±0.9) MeV. The intensity of the 10B primary beam can reach to 150 pnA, and the relevant intensity of the 10C secondary beam is 850 s－1, which can meet the requirements of nuclear reaction experiment.


Fig.2 Scatter plot of ΔE vs. Et

References:[1] KAJINO T, BOYD R N. The Astrophys J, 1990, 359: 267-276.

[2] AXELSSON L, BORGE M J G, FAYANS S, et al. Phys Rev C, 1996, 54:R1 511-R1 514.

[3] MARKENROTH K, AXELSSON L, BAXTER S, et al. Phys Rev C, 2000, 62:034308.

[4] SAVARD G, GALINDO-URIBARRI A, HAGBERG E, et al. Phys Rev Lett, 1995, 74:1 521-1 524

[5] FULIKAWA B K, ASZTALOS S J, CLARK R M, et al. Phys Lett , 1999B, 449:6-11.

[6] BAI X X, LIU W P, QIN J C, et al. Nucl Phys, 1995, A588:273c-276c.

41 Measurement of 17F(d, n)18Ne Reaction

YAN Sheng-quan, LIAN Gang, LI Zhi-hong, LIU Wei-ping, WANG You-bao, BAI Xi-xiang,ZENG Sheng, GUO Bing, WANG Bao-xiang, SU Jun

Explosive hydrogen burning occurs in very massive (M≥105-108 M) star with high temperature and density. Hot pp chain, hot CNO, hot NeNa-MgAl chain and the flowing γp and αp process will play a prominent role in hydrogen burning as the temperature goes higher. When the temperature of the star is higher than 108 K, high temperature CNO chain is dominant in hydrogen burning, with the temperature goes higher to 5×108 K, CNO chain will transfer to NeNa-MgAl chain. 14O(α, p)17F(p, γ)18Ne(α, p)21Na and 15O(α, γ)19Ne(p, γ)20Na reaction chains included in high temperature CNO chain and the high temperature CNO leak mechanism affected the nucleosythesis path and energy generate rate greatly, 17F(p, γ)18Ne is one of the important reactions which involve radioactive nuclei. The cross section of the 17F(p, γ)18Ne reaction is very small at energy range of astrophysical interest. The angular distribution of 17F(d, n)18Ne was used to extract the asymptotic normalization constant (ANC) for the virtual decay of 18Ne→17F+p and the astrophysical S-factor for direct capture contribution in 17F(p, γ)18Ne.


Fig. 1 Schematic layout of secondary beam facility

The measurement of the 17F(d, n)18Ne reaction was carried out in secondary beam facility of the HI-13 tandem accelerator at China Institute of Atomic Energy, as shown in Fig. 1. A 97 MeV 16O primary from the tandem accelerator impinged on a D2 gas target and 17F ions were produced through the 16O(d, n)17F reaction, After the magnetic separation and focus, the 71.8 MeV 17F secondary beam was delivered. The typical purity of 17F beam was about 80% and the energy resolution was about 10%.

The 17F beam was then collimated with two apertures in diameter of 3 mm and directed onto a 1.25 mg/cm2 thick (CD2)n target to study the 17F(d, n)18Ne reaction. The reaction products 18Ne were detected and identified with a ΔE-E telescope, setup was shown in Fig. 2. The telescope consists of a 19.3 μm silicon ΔE detector and a 300 μm 10-annular silicon E detector backed by an independent 300 μm silicon detector. Such a detector configuration covered the laboratory angular ranges of 0° to 6.5°(greater than the maximum θlab of 17F with 6.2°, thus enabled 100% detection of 17F ions due to the inverse kinematics).

Fig. 2 Experimental setup

We have got 3.35×108 17F events, and the angular distribution of 17F(d, n)18Ne is shown in Fig. 3. Because of the poor energy divergence of the secondary beam, the angular distribution θ cm>45°is hard to extract, the theory analysis of the data is in progress.


Fig. 3 The angular distribution of the 17F(d, n)18Ne reaction

42 Determination of Astrophysical 26Si(p, )27P Reaction Rate From Asymptotic Normalization Coefficients of 27Mg → 26Mg + n

GUO Bing, LI Zhi-hong, BAI Xi-xiang, LIU Wei-ping, SHU Neng-chuan, CHEN Yong-shou

The 1.809 MeV -ray from the decay of 26Al is an excellent observable for some astrophysical events, such as novae and X-ray burst. The nucleosynthesis of 26Al is dominated by the reaction chain 24Mg(p,)25Al(+)25Mg(p,)26Al, however, it is complicated due to the presence of a short-lived (T1/2 = 6.34 s) isomer. This dominant chain can be bypassed through 25Al(p,)26Si(p,)27P, and thus 26Si(p,)27P is thought to be one of the key reactions in the production of 26Al. It has been supposed that the thermal equilibrium between the ground and isomeric states of 26Al may be reached at high temperature (T9 ≈ 0.4) novae. The isomeric state of 26Al can also be produced via the reaction chain 25Al(p,)26Si(+)26Alm. Therefore, 26Si depletion via its (p,) reaction is of importance for determining the quantity of 26Algs

produced by the thermal equilibrium because 26Alm would not be fed by 26Si decay.At the temperatures of astrophysical interest, the 26Si(p,)27P reaction is believed to be dominated by

direct capture into the ground state of 27P and the resonant captures into the first and second excited states of 27P. There are some theoretical and experimental studies on this reaction. To date, there has not yet been any experimental information concerning the direct capture rate of the 26Si(p,)27P reaction.

Here we reanalyze the existing 26Mg(d,p)27Mg angular distributions, and deduce the neutron asymptotic normalization coefficients (ANC) for 27Mg → 26Mg + n, based on distorted wave Born approximation (DWBA) analysis. Fig. 1 shows the normalized angular distributions with four sets of optical potential parameters, together with experimental data of 26Mg(d,p)27Mg at Ed = 12 MeV. The proton ANC of 27P → 26Si + p is then extracted using charge symmetry of mirror nuclei, and employed to obtain the 26Si(p,)27P astrophysical reaction rate for the direct capture into the ground state of 27P. We have also derived the proton widths from the neutron ANCs and then computed the contribution of resonant captures into the first and second excited states of 27P. Fig. 2 demonstrates the temperature


dependence of reaction rates for the direct capture into the ground state and the resonant captures into the first and second excited states of 27P. It can be seen that the 26Si(p,)27P reaction is dominated by the resonant capture into the first excited state of 27P in a wide range of temperature (T9 = 0.1-1).

Fig. 1 Experimental and the DWBA calculations using four sets of optical potentials

at the ground(a), first(b) and second excited states of 27Mg(c)


Fig. 2 Temperature dependence of reaction rates for direct capture and resonant captures

43 Measurement of Branching Ration of Deuterium Induced Reactions on 2He at 20 keV

ZHOU Jing, FU Yuan-yong, ZHOU Shu-hua, LI Cheng-bo, LIU Zhi-yi, MENG Qiu-ying

Nuclear reactions between light charged particles at low energy play important role in many areas of basic and applied physics. However due to the cross section drops dramatically with the decrease of incident energy, the measurement of the 2He(d,)4He reaction has to be conducted with very low effect and high background. So far the experimental results which have been published are only down to 50 keV incident energy. In the present work we extended the measurement of the branching ratio of 2H(d,)4He reactions versus the 2H(d,p)3H reactions down to a beam energy of 20 keV.

In the experiment, a deuterium-loaded titanium target with Mo backing was bombarded by 20 keV deuteron beam produced by the low energy acceleration facility (LEAF) at China Institute of Atomic Energy. The D-Ti target was about 0.5 mg/cm2 thick with the atomic ratio of deuterium to titanium being 1.7∶1. The beam current was about 5 mA and the size of the beam spot on the target was 10 mm×20 mm. The experimental arrangement is shown in Fig.1. The -rays were detected with a 20 cm×20 cm NaI(Tl) detector, which was surrounded by a 10 cm thick plastic scintillator detector with another 10 cm thick plastic scintillator detector in front as anti-coincidence shield for rejecting the cosmic ray background. Outside of the surrounding plastic scintillator, a shield composed of 10 cm of lead and 38 cm of lithium carbonated paraffin was used to reduce the background -rays and neutrons. The axis of the -ray detector assembly was at 8.5 to the beam. The protons produced from the 2H(d,p)3H reactions were detected with a 8 cm GM type Au-Si surface barrier semiconductor detector placed at the end of a 100 cm long tube, which was perpendicular to the beam line. There were two anti-scattering diaphragms to prevent the scattered protons from hitting the detector and a 3.03 mm collimator to define the solid angle. The proton detector was covered with an aluminum foil of 2 m in thickness to stop the scattered protons and other charged particles. The signals of the NaI(Tl) detector were fed into a multichannel pulse-height analyzer gated by the anti-coincidence signal. Simultaneously, the charged particle signals from the semiconductor detector were analyzed by another multichannel pulse-height analyzer.


The measurement was performed for 126 hours with beam on and also for 1 024 hours with beam off to measure the radiation background which is mainly composed of the remained cosmic ray background and was fitted with a function of y=exp(p0+p1x+p2x2). Fig.1a shows the raw spectra of the -ray channel both with beam-on and beam-off (fitted). There is a peak near channel 145 in the beam-on spectrum. Fig.1b shows the same spectrum with beam-off background subtracted. However, some background still exists mostly due to the neutron induced reactions. This background was fitted with a function of y= p0+p1x+p2x2+p3exp{－0.5[(x－p4)/p5]2} and subtracted from the spectrum in Fig. 1b. Then a clean -ray peak shows up in Fig.1c. This peak corresponds to 23.8 MeV according to the calibration.

Fig. 1 Raw -ray spectrum(a) for Ed (lab)=20 keV and beam-off background spectrum with fit (solid line),

the same spectrum(b) as (a) but with beam-off background subtracted and

neutron induced background with fit (solid line) and -ray spectrum(c) with neutron background subtracted from (b)


By integrating the simultaneously measured 23.8 MeV -ray peak and proton peak, the yield ratio of the -ray versus the proton can be obtained. After the efficiency calibration, the branching ratio is calculated to be /p =(1.060.45)×10－ 7. Fig. 2 shows the measured /p ratios from present work (solid circle) and from Ref. [1] (solid square) and [2] (open square). One can see that within the errors the ratios can be considered as energy independent in the energy range between 10 and 80 keV.

Fig. 2 Ratios in the 10-80 keV D-D c.m. energy range

■—From Ref.[1]；□—From Ref.[2]；●—This work

References: [1] CECIL F E , HALE G M. The science of cold fusion como, Italy: Societa Italiana di Fisica,1991.

[2] WIKINSON F J, CECIL F E . Phys Rev, 1995, C31: 2 036.

44 Study of PHOS Pre-shower Detector Performances

LI Xiao-mei, HU Shou-yang, ZHOU Jing, MENG Qiu-ying, LI Shou-ping

In the LHC/ALICE experiments, photon production will be studied with the PHOS electromagnetic calorimeter. A pre-shower detector has been proposed with a passive converter sandwiched by two MICROMEGAS detectors covering PHOS module to improve the photon identification, with respect to the set-up with only CPV in front of PHOS. The PPSD will considerably improve the rejection of neutral hadrons and the identification of overlapping showers.

The prototypes of PPSD with 8×6 pads in each MICROMEGAS detector have been developed and tested at CERN PS with proton, pion and electron beams of 2 GeV/c and 1 GeV/c momentum. The choice of the gas mixture during the experiment was Ar+10%iC4H10.

In the experiment, the data acquisition accumulated events with two trigger configurations: wide beam (the beam spreads over more than one pad) and small beam (the beam spreads just over one pad). These beam characteristics helped to measure the relative weight of noise and response. With the wide beam trigger (10 cm×10 cm), the selected beam spot is larger than the size of one pad (2.2 cm×2.2 cm).


The beam illuminated the central pad and its neighboring pads. The charge distributions are collected by a single pad of PPSD for different micro-mesh voltages. Each distribution shows two components: one at low amplitudes which corresponds to the intrinsic electronic noise associated with the pad and one at large amplitudes which corresponds to the response to ionizing particles. The intrinsic electronic noise exhibits a Gaussian distribution. This component corresponds to events in which the beam particles selected by the wide beam trigger, hit one of the neighboring pads and the central pad only registered noises. The maximum of the Gaussian distribution is a measure of the V550 pedestal. The width of the Gaussian distribution is a measure of the electronics noise, which depends on the electromagnetic environment and on the capacitance of the pad anode. The second component represents the detector response to ionizing particles and exhibits a Landau distribution. This distribution is a result of the fluctuations in the number of primary electrons created in the drift region. The maximum of the Landau distribution reflects the gain attained in the amplification zone. The width is mainly related to the average number of primary electrons: a smaller average number of primary electrons leading to larger fluctuations. A correlated noise, a noise level common to all pad signals, adds to the intrinsic noise of a pad. It results from the experimental environment, e.g. Inhomogeneities in the detector and readout in addition to energy loss and calibration errors. It can be removed on an event-by-event basis.

We have studied the charge collected on a single pad as a function of the micro-mesh voltage, for voltages ranging from －380 to －450 V. The evolution of the detector gain in the amplification gap as a function of the micro-mesh voltage, HVmesh, for a constant cathode voltage is shown in Fig.1. In the experiment, gas mixture was Ar+10%iC4H10 and the micro-mesh voltage is－1 000 V. The solid line is to guide the eyes， the fit equation is Gain=0.002 7e0.0033HVmesh. In the measured HVmesh range, the gain changes from 6×102 to 8×103. An increase of 20 V of the HVmesh changes the gain by a factor of 2.

Fig. 1 Gain in the amplification gas as a function of the micro-mesh voltage

The detector efficiency has been studied as a function of the gain. The efficiency is defined as the ratio between the integrated area of the Landau distribution starting from nσ (n=2, 3, 4) of the Gaussian maximum and the area of the total integrated Landau distribution. We calculate the efficiency in two ways: with and without correlated noise. The efficiency is considerably improved after removal of the correlated noise. We observe that for HVmesh larger than 400 V (the gain is larger than 103), the detector


efficiency is above 95%. When HVmesh is equal to 450 V, the efficiency reaches 99.6%. The steep decrease of the detector efficiency for HVmesh lower than 400 V is caused by the fact that the gain is too low to induce on the pad a signal larger than the dispersion of the nominal noise.

To study the background induced by the passive converter in the gaseous detectors, we used the small beam trigger selection. Choose 430 V as the micro-mesh voltage. The small beam definition is smaller than the size of one pad. The noise contribution almost disappears on the central pad. For the pads positioned out of the beam trajectory, the amplitude distribution is still dominated by the noise component. With the small beam trigger, we have obtained the following efficiencies: 99.9%, 99.7%, 99.4% calculated from 2σ, 3σ and 4σ of Gaussian maximum.

45 Spectroscopy of Hypernuclei and *

FU Yuan-yong，ZHOU Shu-hua, L I Chen-bo, ZHOU Jing, MENG Qiu-ying

The purpose of this experiment is to study the nuclear medium effect on the magnetic moment of

particles by measuring the life time of the M1 spin flip transition of （7/2+5/2+）as well as to solve

the puzzle by studying the ground state doublet spacing of .

The experiment was conducted at the K6 beam line of the PS accelerator of KEK using the HYPERBALL2 spectrometer which was constructed jointly by TOHOKU University and China Institute

of Atomic Energy. The hypernuclei and were produced through the 12C(+,K+) reactions. About

1.2×1012 of + particles were accumulated. Preliminary analyses have identified 6 lines from (262,

454, 500, 564, 1 428, 2 479 keV) and 2.61 MeV rays from the ground state doublet transition of .

Further analyses are in progress.

Supported by National Natural Science Foundation of China(1987507,10375094)﹡

46 Lifetime Measurements for Electric-Dipole n=0 Transitions in the Beryllium-Like Sulfur*

DU Shu-bin, YANG Zhi-hu1, CHANG Hong-wei, SU Hong（1 Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China)

We have measured the lifetimes of n = 0 allowed transitions in the beryllium-like sulfur using beam foil spectroscopic technique. The measured values, derived from analysis of arbitrarily normalized decay curves, are presented and compared with theoretical calculations and previous measurements (Table 1). Accurate probabilities have been determined by the well-known relationship and were present in Table 2.


The measurements were performed at the heavy ion research facility in Lanzhou (HIRFL) in the Institute of Modern Physics and at the HI-13 tandem accelerator in the China Institute of Atomic Energy (CIAE). The spectra were collected in the 190-530 Å range, where a large number of accurately known lines were available, the spectra were assigned using the wavelength table given by Kaufman and Martin.

Table 1 Wavelengths and lifetimes for Be-like sulfur

TransitionWavelength /Å Lifetime /ps

This Expt. Theory This Expt. Previous Exp. Theory

2s2p1 S0 -2s2p 1Po1 256.67 256.685 129±4 130±15 128

2s2p 1Po1 -2p2 1S0 301.12 300.99 81±5 81±4 84

2s2p 3Po0 -2p2 3P1 303.35 303.384 165±7 164

2s2p 3Po2 -2p2 3P2 308.91 308.953 159±8 168 161, 161,168, 156

2s2p 3Po1 -2p2 3P0 312.53 312.732 176±11 192±15 169, 170

2s2p 3Po2 -2p2 3P1 316.79 316.843 167±8 177±9 164, 165

Table 2 Transition probabilities for some allowed n=0 transition in beryllium-like sulfur

Transition109 transition probability /s－1

This work Theory

2s2 1 S0 -2s2p 1Po1 7.75 7.42, 7.77, 7.81

2s2p 1Po1 -2p2 1S0 12.35 11.91

2s2p 3Po0 -2p2 3P1 6.06 6.10

2s2p 3Po2 -2p2 3P2 6.29 5.96, 6.40, 6.21, 6.1

2s2p 3Po1 -2p2 3P0 5.68 5.92, 5.88

2s2p 3Po2 -2p2 3P1 5.99 6.10, 6.06

* Supported by National Natural Science Foundation of China

47 Experiment Design for Resonant Scattering Reactions With Thick Target*

WANG You-bao, WANG Bao-xiang, BAI Xi-xiang, GUO Bing, LI Zhi-hong,LIAN Gang, LIU Wei-ping, SU Jun, YAN Sheng-quan, ZENG Sheng

The thick-target method for resonant scattering reactions using secondary radioactive ion beams in inverse kinematics attracts a lot of attention, recently. The method makes use of a target, for example (CH2)n, which is thick enough to stop the secondary beams. The measured proton spectrum, after correction of reaction kinematics and energy loss, reveals the excitation function of elastic resonant reaction. A fit of the excitation function gives rise to the energy, spin-parity and p of the resonances. The advantage of the method is that the excitation function for a certain energy range can be obtained by a one-shot run, thus is suitable for the currently available low-intensity secondary beams.


Towards to thick-target experiments on the secondary beam line at HI-13 Tandem laboratory, a setup based on the use of a time-of-flight (TOF) system and large-area double-sided silicon strip detector (DSSSD) is prepared. A schematic drawing of the setup is shown in Fig. 1.

Fig. 1 Thick-target experimental setup

The TOF system is applied for the identification of the components in secondary beams. A gate on the wanted components in the TOF spectrum can be used for the normalization of the cross section, and also for the elimination of the random + background arisen from the decay of the stopped beams in (CH2)n target. For this purpose, two plastic scintillator timing detectors are used, each of which is composed of a 10 m thick BC422 scintillator foil coupled with a Hamamatsu R2083 photomultiplier tube (PMT). The flight path of TOF is 3 590 mm.

Fig.2 TOF spectrum

To cover the full energy range of emitted protons, a E-E telescope which consists of a 63 m thick


DSSSD backed with a 982 m thick silicon detector is installed. Both detectors are of the size of 50 mm50 mm, the DSSSD is position sensitive with a resolution of 3 mm3 mm, defined by the width of microstrips orthogonally oriented on both sides. The E-E telescope is placed at 150 mm downstream from the (CH2)n target to enhance the angular resolution; in addition, the beam spot is refined by a 5mm and 3 mm in diameter collimator complex.

The setup is tested with a 17F secondary beam of about 60 MeV on a (CH2)n target of 7.53 mg/cm2. As an example, a TOF spectrum is shown in Fig. 2. In Fig. 2, the hatched area corresponds to 17F produced via 2H(16O, 17F)n reaction. The purity of 17F is of 44 % in this run, which is much less than the best ever achieved of 82%. The 17F can be identified in TOF with a resolution of 4.5 ns in FWHM.

A Monte-Carlo simulation of the E-E telescope is performed under the same condition. The proton total energy in the center of mass (c.m.) frame versus energy loss in DSSSD is given in Fig.3. It is shown that the threshold is about 200 keV and the resolution is of about 100 keV(both in c.m. frame). Further improvement of the energy resolution can be achieved by analyzing the TOF spectrum. Experiment with the setup using 17F secondary beam for the 18Ne excited states of nuclear astrophysical interest is scheduled.

Fig. 3 Proton total energy in c.m. frame versus energy loss in DSSSD

* Supported by National Natural Science Foundation of China(10445004)

48 Benchmarking of Evaluated Neutron Data for Beryllium by a 14 MeV Slab Transmission Experiment

XIN Biao, BAO Jie, CHEN Lin, JIANG Jing, ZHOU Zu-ying，TANG Hong-qing


The neutron leakage spectra from the surface of the Beryllium slab at 90°have been measured by the time-of-flight method. The measured neutron energy range was from 14 MeV down to 3 MeV. Three dimensional Monte Carlo simulation code MCNP has been used to simulate the experiment. Evaluated neutron data of 9Be from CENDL3.0, ENDF/B-6, JENDL3.3, JEF3.0/3.1 libraries have been selected for the MCNP simulation. The experiment results have been compared with the results simulated by MCNP. The 9Be neutron data benchmark results have been discussed.

49 Sonoluminescence Research in Water Medium

BAO Jie, LIU Yong-hui, HUANG Han-xiong, YANG Jian,FU Qiang, ZHOU Zu-ying, TANG Hong-qing

The necessary instruments have been setup for sonoluminescence characteristic and mechanic research in China Institute Atomic Energy. Some relative parameters have been gotten. The lasting time of flashing light exceed one hour. And some sonoluminescence characters also have been measured, such as dependence of light intensity in water as a function of the relative percentage of air gas, noble gas, temperature; coincidence of sonoluminescence light frequence and source generator output frequence; and angular distribution of sonoluminescence flashing light. It will provide a base for sonofusion research.

50 Systematics Study of the Independent Yields for Neutron-Induced Fission of 235,238U and 239Pu

SHU Neng-chuan, LIU Ting-jin

The fission yields play important rolls in the nuclear engineering, such as the calculations for the decay energy and the poisonous material in reactor engineering. The independent yield is the main part of the fission yields. The systematics of the independent yields was studied for fission of 235,238U and 239Pu induced by thermal, fission spectrum and fast(about 14 MeV) neutron with Zp model, and the data were evaluated. The results were compared with the data from other libraries such as ENDF/B6, JEF-3.0 and JENDL3.3.

51 Further Analysis of Neutron Double-Differential Cross Section of n+16O at 14.1 and 18 MeV

DUAN Jun-feng, YAN Yu-liang, SUN Xiao-jun, WANG Ji-min, ZHANG Jing-shang,

By using a new reaction model for light nuclei, the double-differential cross section of total outgoing neutron with LUNF code for n+16O reactions at En=14.1 MeV and 18 MeV have been calculated and analyzed. The opened reaction channels, which have contribution to emit the neutrons, are listed in detail. To improve the fitting results the direct inelastic scattering mechanism is involved. The calculated results agree fairly well with the experimental data at En=14.1 MeV and the deviation from calculated results and


experimental data in low energy region at En=18 MeV has been analyzed. Since the possibility of 5He has been affirmed theoretically, so 5He emission from n+16O reaction is taken into account, which play important role at the region of the outgoing neutron energy εn<3 MeV in total outgoing neutron energy-angular spectrum. The calculated results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil effect in light nuclear reactions is essentially important.

52 Theoretical Analysis of Neutron Double-Differential Cross Section of n+19F at 14.2 MeV

DUAN Jun-feng, YAN Yu-liang, SUN Xiao-jun, ZHANG Yue, ZHANG Jing-shang

A new reaction model for light nuclei of 1p shell is expanded to 19F with 2s-1d shell nucleus. The double-differential cross sections of total outgoing neutron for n+19F reactions at En = 14.2 MeV are calculated and analyzed, and the calculated results agree fairly well with the experimental measurements. The contributions from different reaction channels for the double-differential cross sections of total outgoing neutron are analyzed in detail. The contributions of the second neutron from (n,2n) reaction channel dominate the low energy region of the double-differential cross section, whereas the neutrons of 5He separation contribute to this region indistinctively. The continuous level has been employed in the former nuclear reaction model, in fact this is an approximate approach from the theoretical calculation point of view, while all of the residual states are the discrete levels in the n+19F reaction. In this way the much more accurate physical picture can be given.

53 Pre-formation Probability of 5He Cluster in Pre-equilibrium Mechanism

DUAN Jun-feng, YAN Yu-liang, ZHANG Jing-shang

The possibility of 5He cluster emission has been affirmed theoretically. In order to describe the emission probability of 5He cluster, the pre-formation probability of 5He cluster in pre-equilibrium emission process is need to be established. In terms of Iwamoto-Harada model, the theoretical formula of pre-formation probability of 5He cluster including 1p shell nucleon in pre-equilibrium mechanism has been established and calculated. In the case of low incident energies, the configuration of [1,m] for 5He cluster is the dominant part in the nuclear reaction. The calculated results indicate that pre-formation probability of configuration [1,m] for the unstable 5He cluster is much smaller than that of d,t,3He, and 4He light stable composite particles, which is consisted of only 1 s shell nucleons. However, it is propitious to the emission of 5He from the point of view on threshold energies, since the binding energies of 5He are generally lower than that of 3He in compound nucleus. The corresponding model formula has been given in this paper for described pre-formation probability of 5He cluster in pre-equilibrium mechanism.


54 5He Emission in Neutron Induced 10B Reactions

WANG Ji-min, DUAN Jun-feng, YAN Yu-liang, SUN Xiao-jun, ZHANG Jing-shang

The possibility of 5He cluster emission for neutron induced light nucleus reaction has been affirmed theoretically. 5He is unstable and separated into a neutron and an alpha particle spontaneously. The neutron from 5He breakup process contribute to the low energy region of the total outgoing neutron double-differential cross sections, and the calculated results could improve the fitting with the double-differential measurements. In addition, the calculated results show the fact that the 5He cluster is emitted mainly from the pre-equilibrium emission process in n+10B reactions. In n+10B reactions, 5He cluster emission has been discussed with the updated level scheme and the new optical model parameters. In this paper the reaction channels related to 5He emission are listed in detail. By using the new reaction model for light nuclei, the double-differential cross sections of total outgoing neutrons for n+10B reactions at En=14.2 MeV have been calculated, which agree fairly well with the double-differential measurements. Particularly, in the energy-angular spectra the contribution from the -emission to the total outgoing neutron double-differential cross sections has also been analyzed. To show the contribution from the 5He-emission the partial energy-angular spectra of 60o at En=14.2 MeV have been given. Indeed, once the 5He emission is taken into account, the fitting with the double-differential measurements of total outgoing neutrons at the low energy region could be improved. Therefore, to consider the 5He emission properly in the reaction processes of light nuclei is necessary.

55 Double-Differential Cross Section of 5He Emission

YAN Yu-liang, DUAN Jun-feng, ZHANG Jing-shang, XU Guang

The probability of 5He particle emission has been affirmed theoretically. In order to describe the 5He emission, the theoretical formula of the double-differential cross section of emitted 5He is established. Based on the pick-up mechanism, used for calculating the formula of d, t, 3He and emissions, the theoretical formula of double-differential cross section of 5He is obtained, which is expressed in the form of Legendre coefficients. In the case of low incident energies, the configuration is the dominant part in the reaction processes.

The calculated result indicates that the forward peaked angular distribution of the composite particle emission is weaker than that of the emitted single nucleon due to pick-up nucleon from the Fermi sea. As an example, the reactions of n+14N have been calculated, and the Legendre coefficients of d, t, 3He, and 5He emissions are obtained respectively.

The results show that the forward tendency is decided by the average momentum per nucleon in the emitted composite particles. The larger the average momentum is, the stronger the forward tendency is.

56 Theoretical Analysis of Neutron Double-Differential


Cross Section of n+14N at 14.2 MeV

YAN Yu-liang, DUAN Jun-feng, SUN Xiao-jun, WANG Ji-min, ZHANG Jing-shang

By using a new reaction model for light nuclei, the double-differential cross section of n+ 14N reactions at En=14.2 MeV have been analyzed. In the case of n+14N reactions, the reaction mechanism is very complex, there are over one hundred opened partial reaction channels even at incident energy En=14.2 MeV. The opened reaction channels are listed in detail. With LUNF code the model calculation is performed to analyze the double-differential cross sections of total outgoing neutron. The calculated results agree fairly well with the experimental data. The results indicate that the pre-equilibrium mechanism dominates the whole reaction processes, and the recoil effect in light nuclear reactions is essentially important. 5He emission has been considered, but it is only a small contribution to the double-differential cross section at En=14.2 MeV.

57 Ni and Ni Alloys Fabricated by Spark Plasma Sintering System*

LI Mei-juan, LIU Dan-min1, GOU Cheng, ZHANG Bai-sheng, CHEN Don-feng, LIU Yun-tao

（1 Beijing University of Technology）

Generally the high temperature superconducting substrates of Ni and Ni alloys can be prepared by casting method and powder metallurgy method. The casting method has a weakness that a columnar or dendrite structure can be induced in the ingot, restricting the formation of preferred texture through rolling and annealing. The powder metallurgy method consisting of powder mixing, compaction, and sintering, is considered to be more complicated. Spark Plasma Sintering is a sintering technology developed in recent years. It has many inherent advantages compare with traditional sintering techniques, such as, 1)The fast heating and cooling rates; 2) Special sintering mechanics; 3) Lower Sintering temperature; 4) Better self-purification of the surface of the particle and sintering activity; 5) Simple operation system; 6) Wide application, the SPS system enables the sintering of metals, ceramics, polymers and the composite materials.

We fabricated a serious of high temperature superconducting substrate of Pure Ni by Spark Plasma Sintering (SPS) system 3.20-MK-V for the first time, and successfully obtained high density Ni samples. The relationship between sintering temperature and sample density was investigated. The relative densities of as-sintered pure Ni are plotted as a function of sintering temperature in Fig. 1. From Fig. 1 we can see that the sample relative density increases with the sintering temperature increasing.

Fig. 1 Relationship between relative density of as-sintered pure Ni and sintering temperature


* Supported by Nation “863” Program of China(2002AA306221)

58 Structural Study on Zr0.9Ti0.1MnCr Laves Deuterides by Neutron Powder Diffraction*

SUN Kai, LIU Yu-tao, WANG Hong-li , GUO Xiu-mei1, WU Er-dong1

(1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China)

The Zr and Ti elements can combine with 3d transition metals to form AB2 type Laves phase alloys in one of the two structures, namely cubic C15 and hexagonal C14 structures. In the Laves phase, all interstices are formed by tetrahedrons. As a result, the hydrogen absorption of these Laves phases increases the size of the unit cell continuously without changing the host structure. This property makes these Laves phase as a model substance for structural investigation of hydrogen sorption. There are three types of tetrahedral interstices in each formula unit of Laves phase, i.e. 12 A2B2-type, 4 AB3-type and 1 B4-type. In previous studies of the hydrogen occupation of the alloys, it was shown that hydrogen atoms can only take less than half of the totally 17 interstices per formula unit, and they prefer to occupy the A2B2-type and AB3-type interstices, while B4-type are never occupied.

In these Laves phase alloys, the alloys of (ZrxTi1－x) (MnyCr1－y)2 with C14 structure have exhibited good properties for hydrogen storage. We have recently studied the hydrogen activation and sorption properties of one of these alloys with the composition of (ZrxTi1－x)MnCr.

The Zr0.9Ti0.1MnCr alloy was prepared by arc melting 99.9% pure raw materials under an argon atmosphere. The sample was encapsulated in quartz tube with argon and annealed at 900 ℃ for 72 hours. 6.5 g sample was activated using 99.9% pure D2 gas in a Sieverts-type hydrogenator at about 150 kPa and 200 ℃. During deuterization, the sample was contained in a cylindrical null-matrix Ti-Zr alloy container cell. The surface of the cell was passivated by deliberately oxidation, and tested under the working conditions.

The XRD measurement for the alloy indicates that the Zr0.9Ti0.1MnCr is single-phase C14-Laves structure with a=5.036 Å(1 Å=0.1 nm), c=8.271 Å. The Ti/Zr atoms are randomly located in 4f (z=0.44) site, and Mn/Cr atoms in 2a and 6h (x=0.83) site under space group P63/mmc. As shown in the neutron diffraction pattern, an obvious feature of the deuterides is the existence of the strong background and a broad diffuse hump. However, The crystallized deuteride phase has the C14-type Laves structure in P63/mmc. The D atoms randomly occupy four tetrahedral interstices of 6h1(x=0.42), 6h2(x=0.17), 12k(x=0.42, z=0.66) and 24l(0.22,1.03,0.08) formed by two Ti/Zr atoms and two Mn/Cr atoms. The refined D occupancies of different interstices for the deuterides could vary significantly, but the variations of the refined positional parameters for D atoms in the three deuterides remain within the last decimal figures. This situation is similar to that of the D occupancies in ZrV2Dx.

The D occupancy of different tetrahedron sites is mainly determined by atom affinity and interstitial size. In the present work, only A2B2 sites are occupied, but not with equal probability. The differences in atom affinity and interstitial size for A2B2 sites in the Zr0.9Ti0.1MnCrD3.5 may be indicated by the distance between the center of the interstices and four atoms forming the tetrahedron. The minimum distance at 6h1, 12k, 24l and 6h2 sites is 2.064, 1.939, 1.818 and 1.633 Å, respectively. Moreover, the minimum distance at 6h1 and 12k is closer to “A” atoms, so the D atoms entering 6h1 and 12k sites can form more


stable deuteride than entering 24l and 6h2 sites, at which the minimum distance is closer to “B” atoms. This analysis is consistent with neutron diffraction results.

* Supported by President Foundation of China Institute of Atomic Energy

59 Structural Study on Ti-Mo Deuterides

SUN Kai, LIU Yu-tao, WANG Hong-li, GUO Xiu-mei1, WU Er-dong1

(1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China)

The interaction between Ti and H has been widely studied under atmospheric or high pressure for decades. After absorbing hydrogen, the hcp -Ti can form a solid solution of bcc -TiHx, then turn into bct -TiH or fcc -TiH2－y hydrides at a proper temperature. The -phase or -phase hydride precipitations cause strong embrittlement due to a large volume expansion in the phase transitions. The high temperature phase -Ti has bcc structure. Mo is a common -Ti stabilizing element. It decreases the to -Ti phase transition temperature to room temperature. Moreover, like -Ti, Ti-Mo alloy can absorb a mass of hydrogen to form stable -phase hydride at moderate pressure and temperature, and the hydride has relatively higher strength. Thanks to these properties, some studies have been carried out for the hydrogen-storage properties of the Ti-Mo alloys. However, so far, the studies on the Ti-Mo alloys and their hydrides are still insufficient, especially on the structural studies. Recently, we have studied the deuteride of a Ti-33a.t.%Mo alloy by neutron and X-ray powder diffraction, and revealed some interesting structural information of the deuteride. In this work, we extend our structural studies to a series of deuterides of the Ti-Mo alloys with Mo contents ranging from 5 to 40 a.t.% using neutron diffraction techniques. After deuterization at about 150 kPa, the saturated deuterides containing about 1.8 to 1.9 deuterium per alloy atom with a -phase titanium hydride type of structure have formed. The lattice constants of the deuterides decrease consistently with the increase of the Mo contents.

The XRD measurements suggest that structures of the alloys are generally consistent with the Ti-Mo phase diagram. The Ti-Mo alloy containing 5 a.t.%Mo is composed of hcp -phase (6 w.t.%) and bcc -phase. Only single -phase was observed in the XRD patterns of other Ti-Mo alloys with higher Mo contents. Regardless the initial structures of the alloys, only single -phase titanium hydride type of deuterides were formed after deuterization. The results of neutron diffraction show that the peaks corresponding to a fcc unit cell can be identified and fitted by a structure of the -hydride of Ti metal in all these patterns. In the -hydride type of structure under space group Fm-3m, the Ti and Mo atoms are randomly located in the 0, 0, 0 and other three equivalent positions (4a), whereas the deuterium atoms can be situated in the tetragonal interstitial sites of 1/4, 1/4, 1/4 and other seven equivalent positions (8c).

A dislocation-induced lattice deformation model had been used to correct the line broadening of the diffraction patterns of one of the Ti-Mo alloy deuterides, and revealed some interesting information on the lattice deformation of the deuteride. The levels and anisotropies of the lattice deformations of the deuterides have both decreased as the increasing Mo content in the deuterides. The enhanced strength of the deuterides due to the alloying Mo is likely to contribute to the reduced lattice deformation of the deuterides.


60 β-NMR Study on 29P (I=1/2+, T1/2=4.14 s)*

ZHOU Dong-mei, ZHENG Yong-nan, YUAN Da-qing, WANG Zhi-qiang, LUO Hai-long, ZUO Yi, LIU Meng, XU Guo-ji, ZHU Sheng-yun

A. Navin and some others have confirmed that there exists halo structure in 26,27,28P isotopes. Chen Fence and some others got the same result with different theoretical models. At the same time, they plotted the total density distribution of protons and neutrons of 25-31P changes with the radius. The figures showed that the proton density distribution of 25-31P has long tail and the tail decreases as the mass number increases. The proton density distribution of 29P obviously has long tail.

The last proton separation energy of β-emitting nuclei 29P is 2.748 MeV. Its last proton and neutron are in 2s1/2 and 1d5/2 orbits, separately. At present, only Wei Yibin et al. studied the structure of 29P (I=1/2+, T1/2=4.14 s) with momentum density distribution and they got the result that the proton-skin structure may exists in 29P. Our present work is to measure the magnetic moment of 29P and study its structure on 2×1.7 MV tandem accelerator with β-NMR technology.

The 29P (I=1/2+, T1/2=4.14 s) nuclei were produced through the 28Si(d,n) 29P reaction with an incident deuteron beam from the 2×1.7 MV tandem accelerator. SiO2 target with a thickness of 40 g/cm2 was used. The SiO2 was evaporated in vacuum on the 0.5 mm thick Ti backing. The target was attached on the target holder that was cooled by a water flow, which ensures the bombardment of a 5-10 beam current. The glancing angle of the target was 5° to the incident beam. The incident deuteron energy was Ed=3.0 MeV. The 29P nuclei were recoiled into the single crystal Si stopper at the recoil angle of 15°-25° through a Cu collimator.

In order to control the change of polarization, a pulsed rf magnetic field H1＝0.5 Gs was applied perpendicular to the externally applied magnetic field H0. The modulation width is 0.2 kHz. In order to reduce un-wanted backgrounds the beam was pulsed and its width was 5 s and the repetition period was 9 s. A beam pulse was followed by a 500 ms rf pulse. The -ray counting started at the end of the rf pulse and lasted to the next beam pulse.

A typical β-NMR spectrum was got for 29P implanted into Si stopper at an externally applied magnetic field of 4.300 kG and at room temperature. A Gaussian fit of the measured β-NMR spectrum gave a resonance frequency of (8 079.7±0.2) kHz. Analysed From the measured resonant frequency and the diamagnetic correction, the magnetic moment can be easily deduced to be μ＝(1.234 6±0.000 3) nm. The measured polarization was approximately 2.6% at the recoil angle of 15°-25°.

The measured magnetic moment is less than that a half of the pure single particle resonance state calculated by single particle model, which demonstrates that the ground state of 29P is not pure single particle state. There exists the configuration mixture. It is difficult to draw definite conclusion for the halo structure of 29P only with the magnetic moment. Further study is undergoing.

* Supported by National Natural Science Foundation of

China（10435010）and Superintendent Foundation of Department of Nuclear Physics


61 Proton-Skin Structure in 17F*

ZHOU Dong-mei, ZHANG Xi-zhen, ZHANG Zhun-lei, ZHENG Yong-nan, YUAN Da-qing, ZUO Yi, LIU Meng, ZHU Sheng-yun

In the present work, we studied the quadrupole resonance in the proton drip line nucleus, 17F, using the self-consistent Hartree-Fock calculation plus the random phase approximation with Skyrme interactions. Including both the isoscalar and the isovector correlation the RPA response function is calculated in the coordinate space so as to take properly into account the continuum effect.

The RPA strength function is

(1)

In Eq.(1) ,Q expresses one-body operators, as for isoscalar quadrupole strength

and for isovector quadrupole strength.

Calculation result gives us the distribution of the quadrupole strength, as shown in Fig.1. By anaylsed Fig.1, we could see that the isoscalar and the isovector correlations and the isosalar giant quadrupole resonance are consistent with that given by the macroscopic collective model.

Fig . 1 Calculated RPA quadrupole strength of 17F as a function of excitation energy

From the result of particle-vibration coupling model with Hartree-Fock single-particle wave functions and random phase approximation response functions, we studied the proton effective charge of 17F.

The core polarization charges for quadrupole transitions are defined as

(2)

(3)

The proton and neutron core polarization charges are written as (4)


(5)Calculation result gives that when the last separation energy is 0.6 MeV the proton effective charge of

orbit d5/2 of 17F is .

We have measured the quadrupole moment of 17F with -NQR method before. From which the proton effective charge of was deduced.

Our theoretical value is consistent with the upper limit of our experimental value. As to nuclei 17F, which is consist of the core of 16O and the last proton in orbit d5/2, its proton effective charge might be small.

Because of high Coulomb and centrifugal barriers the proton halo could not appear in 17F ground

state. Our experimental value of proton effective charge demonstrates that there exists a

proton skin in the I /＋ ground state in 17F.

* Supported by National Science Foundation of China（10435010, 10175088）and Superintendent fund of Department of Nuclear Physics

62 Investigation of Hydrogen Alloys by Positron Annihilation and PAC

ZUO Yi, ZHENG Yong-nan, ZHOU Dong-mei, YUAN Da-qing, LIU Meng, WANG Zhao-hui, DUAN Xiao, ZHU Sheng-yun

In the present work two hydrogen storage alloys Pd0.75Ag0.25 and LaNi4.25Al0.75 are studied by the positron annihilation and perturbed angular correlation techniques.

The Pd0.75Ag0.25Hx alloys with a hydrogen concentration ranging from 0 to 0.35 are investigated by the positron annihilation lifetime measurement method in the temperature region between 77-295 K. The measured lifetime spectra are well characterized by two positron annihilation lifetimes. The short lifetime τ1 is ascribed to the free positron annihilation lifetime and is independent of temperature and hydrogen concentration. This indicates that no phase transition occurs. The long lifetime τ2 is attributed to the one of annihilation of positrons trapped by the defects of hydrogen bubbles. τ2 and its intensity I2 do not vary with the temperature, while τ2 increases and I2 decreases with the increase of hydrogen concentration. The obtained results reveal the growth of the hydrogen bubbles in size and the reduction of bubble concentration with the increase of the hydrogen concentration.

The Pd0.75Ag0.25Hx alloys are also studied by the perturbed angular correlation method at room temperature. The quadrupole interaction frequency is determined to be zero for the Pd0.75Ag0.25 alloy with no hydrogen charging, showing that the 111Ag/111Cd probe nuclei are located in the substitutional site in the Pd0.75Ag0.25 alloy with a fcc structure, and do not experience any electric field gradient interaction. After hydrogen charging a part of the probe nuclei feel perturbation from hydrogen bubble defects, and the quadrupole interactions are observed at the hydrogen concentrations of x=0.1, 0.2 and 0.35. The experimental results illustrate that the quadrupole interaction frequency and its intensity decrease with the increase of hydrogen concentration, demonstrating the growth of the hydrogen bubble size and the reduction of bubble concentration with the hydrogen concentration increase. The width of the quadrupole interaction frequency distribution is measured as well, which shows the hydrogen diffusion effect to some extent. The measured widths tell us that diffusion effect is less with the hydrogen concentration increase.


The experimental results obtained by the positron annihilation and perturbed angular correlation are in good agreement. In addition the hydrogen diffusion is detected by the perturbed angular correlation.

The perturbed angular correlation is used to investigate at room temperature the LaNi4.25Al0.75Hx

alloys with the concentrations of x = 0 and 3. Only one quadrupole interaction frequency of ω1 = 14.39 Mrad/s (V1

zz = 10.1×1017 V/cm2) is detected for the LaNi4.25Al0.75 alloy without hydrogen charging. An additional quadrupole interaction frequency of ω2 = 20.63 Mrad/s（V2

zz = 14.48×1017 V/cm2）appears in LaNi4.25Al0.75Hx with the hydrogen concentration of x = 3. The fraction of ω1 is f1 = 25.1%, and f2 = 74.9% for ω2. The measured ω1 is ascribed to the probe nuclei whose neighboring interstitial site are filled with no hydrogen, and ω2 is interpreted as related to the probe nuclei in the basal plane next to hydrogen-filled octahedral interstitial sites in the same plane. The experimental results show that hydrogen fills preferably the octahedral interstitials, and the partial substitution of Al for Ni would cause the lattice expansion and deformation, which favors the filling of hydrogen into octahedral interstitials.

The Pd0.75Ag0.25Hx alloys are investigated by both the positron annihilation and perturbed angular correlation for the first time and the experimental results obtained by them are well consistent. The present work first investigates the LaNi4.25Al0.75Hx alloys with 140La-140Ce probe nuclei directly produced in the alloys by nuclear reaction, and observe the preferable filling of hydrogen into octahedral interstitials.

* Supported by CNNC Fundation（4160205030103）

63 Measurement of 36Cl With Gas-Filled Time-of-Flight Method

GUAN Yong-jing, HE Ming, JIANG Shan, RUAN Xiang-dong1,WANG Hui-Juan1, WU Shao-yong, DONG Ke-jun

(1 Physics Science and Engineering Technology Department, Guangxi University, Nanning 530004, China)

Some improvements of the gas-filled time-of-flight detector system were achieved. The thickness of the entrance window is decreased to 0.5 micron. A larger area surface barrier detector with the diameter of 40 mm was used to enlarge the detection efficiency. The detection efficiency is higher than 70%. A series of AgCl standard samples (n(36Cl)/n(Cl) about 10－9, 10－10, 10－11 and 10－13) were measured by the gas-filled time-of-flight detector with the incidence energies of 64, 48, 36 and 33 MeV, respectively.

Experimental results show that 36S and 36Cl was identified just from the TOF spectrum for the AgCl(n(36Cl)/n(Cl) about 10－11) standard sample with the above energies whether the 36S content in the samples is lower than 10－ 10 . 36S and 36Cl from the AgCl (n(36Cl)/n(Cl) about 10－ 14) sample can be identified after gated with the incidence energy about 40 MeV. The advantage of the gas-filled time-of-flight method is the higher sensitivity since one more signal can be provided.

64 Measurement of Trace Potassium Contaminations With Accelerator Mass Spectrometry*

DONG Ke-jun, HE Ming, JIANG Shan, WONG Henry Tsz-king1, QIU Jiu-zi2,


GUAN Yong-jing, WU Shao-yong, LI Shi-hong, LIN Min, ZHOU Duo,YIN Xin-yi, PENG Bo3, DING Yan-qiu3, JU Zhi-ping3, YUAN Jian

(1 Institute of Physics Academia Sinica, Taibei 11529, China;

2 Armed Police Force Academy, Langfang 065000, China; 3 Guangxi University, Nanning 530004, China)

It is important to measure the rare long-life radioisotopes such as 40K, U and Th etc. in neutrino detector material. A new method based on Accelerator Mass Spectrometry (AMS) has been developed for measurement of potassium in CsI and LS (Liquid Scintillators). A series of 40K standard samples were made and chemical procedures were explored for LS sample to make the samples suitable for AMS measurement. The experiment result shows that the content of 40K is about 1×10－ 10 g/g in CsI, about 1.3×10－13 g/g in LS and about 7×10－16 g/g in LS without PPO(1,3,5-trimethylbenzene), respectively.

* Supported by National Natural Science Foundation of China

65 The Measurement of 182Hf With AMS

QIU Jiu-zi 1, JIANG Shan, HE Ming, YIN Xin-yi, DONG Ke-jun, GUAN Yong-jing, WU Shao-yong , YUAN Jian , YANG Bing-fan

（1 Armed Police Force Academy, Langfang 065000 , China）

82Hf is a long-lived radionuclide of particular interest for the early history of the solar system[1, 2]. The measurement of 182Hf has been performed with a 13 MV tandem accelerator(HI-13) mass spectrometry at China Institute of Atomic Energy.

In this work, 182Hf was produced through irradiating 50 mg HfO2, enriched in 180Hf to 98.3%, with the high neutron flux of the heavy water research reactor at China Institute of Atomic Energy for eighteen days. After the irradiation, 182Hf/180Hf atom ratio in the sample measured with a thermal ionization mass spectrometry (TIMS) was (1.628±0.011)×10 － 6. Standard samples with 182Hf/180Hf atom ratios of (3.34±0.05)×10－ 8 and (3.30±0.05)×10－ 10 were prepared using irradiated sample and enriched 180Hf O2

respectively.Although the main interference, the stable isobar 182W, can be significantly reduced by extracting

HfF5－ from ion source[3], chemical separation is necessary for further improving the sensitivity. For

chemical separation, the irradiated sample was prepared to chemical formation of HfF4 first, then HfF4 was dissolved in 50 ml 1 M HF solution for column separation. A 1ml sample solution was loaded onto an

anion exchange column. The column was rinsed with 10 ml of 1 M HF. Hf was then eluted by 30 ml of 0.01 M HF-9 M HCl, while W and Ta retained on the column. Tracer experiments showed that the average chemical yield of Hf was greater than 95%, and the decontamination factors for W and Ta were larger than 1 000.

The HfF4 powder was pressed into the target holder, the HfF5¯ ions were extracted from MC-SNICS ion source and Hf 9+ ions with energy of 78 MeV was selected by the analyzing magnet. A golden-silicon surface barrier detector (as energy detector) combined with a time of flight detector are used for the ion identification. Energy-time of flight two-dimension spectra of 182Hf is shown in Fig.1. A ion source yield of about 0.34% for HfF5¯ and a transmission efficiency of about 0.50% for 182Hf were obtained in our AMS facility. In sum the overall efficiency for 182Hf measurements with our setup was about 1.7×10－5.


We can deduct 182W contribution through the measurement of 183W in the same sample. The detection limit of 182Hf/180Hf ratio was obtained to be 2.2×10－10 for our AMS facility.

Fig.1 Two-dimension spectrum of 182Hf

References:[1] NORMAN E B, SCHRAMM D N. Nature, 1983,304:515-517.

[2] VOCKENHUBER C, OBERLJ F, BICHLER M, et al. Physics Review Letters, 2004, 93:1 725 011-1 725 014.

[3] VOCKENHUBER C, BICHLER M, GOLSER R, et al. Nucl Instrum. Methods, B223-224:823-828.

66 Measurement of 36Cl Content in Thermal Groundwater With AMS

HE Ming, JIANG Shan, WU Shao-yong, DONG Ke-jun, GUAN Yong-jing

The content of 36Cl in the groundwater is one of the key data for judging the age of groundwater. The replenishment and the movement of groundwater can be obtained based on the age of the groundwater. These values are crucial to its management and use.

Thermal groundwater is one of the important resources. In order to carry out the study of thermal groundwater, we cooperate with China University of Geosciences to measure the content of 36Cl in the thermal groundwater. the groundwater in the area of Beijing and Tianjin were collected. The AgCl, which is suitable for AMS measurement, was prepared from the groundwater by using chemical procedures, finally the content of 36Cl in the samples were measured with AMS. The results shown that the 36Cl/Cl ratios for most of samples are in the range of 4.410－13 to 2.510－ 14, this range is reasonable for the groundwater. But there is one sample which the ratio of 36Cl/Cl is obviously higher than this range. The high ratio maybe be relative to the groundwater surrounding content of U and Th, this will be affirmed further.

To get the age of the groundwater there are still some factors need be concerned such as the content of Cl－ in the groundwater and the secular equilibrium value of 36Cl. These date will be analysised in next


step.

67 Preparation of 151Sm AMS Standard Samples: Chemical Separation of Eu From the Sample of Sm

YIN Xin-yi, ZHANG Jin-song1, HE Ming, JIANG Shan (1 Nuclear Power Institute of China, Jiajiang 610005, China)

151Sm with its half-life of 90 years is a long-lived radionuclide. It is very interesting for nuclear physics, environment sciences and life sciences to detect trace amounts of 151Sm. AMS with high sensitivity is a kind of nuclear technique for the measurement of trace amounts of 151Sm. AMS is a relative measurement method, which requires standard samples. The interference of Eu is very strong in the measurement of 151Sm with AMS and Thermal Ionization Mass Spectrometry (TIMS), so chemical separation is necessary. The reducing method with zinc powder is used. The principle of this method is that europium can be more easily reduced than samarium and the characters of Eu2+ and Sm3+ are very different. The zinc powder reducing and P204 resin extraction method were used to separate Eu in this paper. The procedure is presented as follows:

The reducing column was filled with 80-100 mesh zinc powder which was pretreated, and the extraction column was filled with P204 resin, then the extraction column was washed and balanced with different concentration hydrochloric acid.

The pH of the sample solution was adjusted to 2-3, then the solution passed through the two columns with the elution velocity of 1.0 mL/min. The two columns were washed with 20 mL ionized water, and europium was eliminated from the extraction column with 20 mL 0.03 mol/L hydrochloric acid. Then samarium was washed from the extraction column with 30 mL 2.0 mol/L, the extraction column was washed with 20 mL 6 mol/L hydrochloric acid eventrally. In order to eliminate europium as much as possible, the procedure was repeated for three times.

The sample solution after chemical separation was precipitated with saturated oxalic acid to form oxalic samarium. The precipitation was washed with 0.2% oxalic acid for three times and was calcined into oxides in the muffle with the temperature 900 ℃ for two hours.

The recovery efficiency of samarium for the chemical procedure is about 90%, and the decontamination factor of Eu is about 103. The content of europium is less than 10 ppb after separation, which can satisfy AMS measurement.

68 Production of Sm Negative Ions for AMS Measurement

YIN Xin-yi, HE Ming , DONG Ke-jun, JIANG Shan

151Sm with its half-life of 90 years is a long-lived radionuclide. It is very interesting for nuclear physics and environment science to detect trace amount of 151Sm. But the content of Sm in samples is very low especially in biological samples (ppm-ppb), it is difficult for routine analyzing technique to detect trace amount of 151Sm, so accelerator mass spectrometry (AMS) is the best choice for the measurement of Sm with high sensitivity. But Sm belongs to the rare earths, it can deteriorate the ionization efficiency of


the ionizer because of its characteristics such as low vapor pressure and low work function. The phenomenon is called the ionizer poisoning, the current decreases rapidly. So resolving the problem of ionizer poisoning is the key factor for 151Sm AMS measurement.

For the cesium sputter ion source, the ionization energy of Cs (3.89 eV) is lower than the work function of molybdenum (4.6 eV) as the ionizer element. Therefore the most outer electron of Cs easily transfers to the ionizer, and the ionization efficiency is almost 100% at the surface temperature of over 1 000 ℃. Negative ions and neutral elements are ejected from the cathode by Cs+ sputtering, then are extracted with a puller electrode. Sputtered neutral Sm atoms that stick to the ionizer deteriorate its ionization efficiency because the work function of Sm (2.7 eV) is lower than the ionization energy of Cs (3.89 eV). The ionizer can’t operation stably for a long time, which is called the ionizer poisoning.

We have resolved the problem by using tungsten cathode, mixing samples with tungsten or molybdenum powder, and changing the depth of sample in the cathode. The design is based on the two ideas: 1) the ionizer surface should be free from being exposed to recoil samarium by covering the cathode surface with tungsten. 2) the solid angle formed by the cathode hole is almost equal to that of the center hole of the ionizer from the cathode. Thus we could control the emission angle from the cathode to the ionizer and restrict the poisoning effect.

As a result, damage to the ionizer decreased, and stable operation of the ion source was successfully achieved with a SmO－ beam current of 105nA at CIAE HI-13 tandem AMS facility (the abundance of 154Sm is 98.6%). And we can make a primary conclusion based on the experimental results, Sm 2O3

performed well. Moreover, Eu suppression can be achieved using SmO－ ions. So Sm2O3 may be the proper chemical form of Sm for the AMS measurement.

69 Measurement of 99Tc Content in Environmental Sample With AMS

PENG Bo1, HE Ming, WU Shao-yong, GUAN Yong-jing, RUAN Xiang-dong1 , JIANG Shan(1 The Physics Department of Guangxi University, Nanning 540003, China)

In order to carry out the environmental application with 99Tc, the measurement method for the water sample and soil sample in the environment have been preliminarily developed. One liter water sample and 10 grams soil sample were collected for sample preparation. In order to check the chemical recovery for the sample preparation, the 95Tcm, which was produced by irradiation with proton, was used as a tracer, and ion-exchange resin named TEVA was used for effective removing background and Tc recovery during the sample preparation. After these chemical procedures, the Tc solution and a quantity of Nb solution were mixed together and evoperated to dry, then this sample can be used for AMS measurement. According to the results of the 95Tcm tracer, the recoveres are about 90% and 50% for water sample and soil samples, respectively. Finally the content of 99Tc in the samples was measured with AMS technique. The results shown that the 99Tc content in the water sample is about 1011 L－1, and 109 g－1 for soil sample, respectively.

70 Re-measured for Half-Life of 97Zr


HUANG Dong-hui, WANG Ping-sheng, TIAN Wei-zhi, NI Bang-fa, LIU Cun-xiong, ZHANG Gui-ying

The half-life of 97Zr, used for the calculation of thermal/epithermal neutron flux ratio in k0-NAA, is re-determined using three measurement systems with different pulse processing principles. The result of (16.7550.013) h clarifies the discrepancy between two widely used literature values, (16.7440.011) and (16.900.05) h.

About 5 mg each of two pieces of high purity Zr foil (99.99%) were irradiated for 1.5 h in the Heavy Water Research Reactor (HWRR) of CIAE. The thermal and epithermal neutron fluxes are 41013 and 41012 cm－2•s－1, respectively, in the irradiation position. After 24 h decay, the activated samples were respectively measured on two HPGe detectors connected to three amplifier/analyzer systems. Time-series measurements were made on 658 and 743 keV peaks. The measurement systems and conditions are summarized in Table 1.

Table 1 Description of 97Zr Half-life Measurement

No Detector/Amplifier ADC/MCA TDM NP SMI/s ND Td Corr mode

1aCanberra HPGe,35%,

1.8 keV/Canberra 2025

Nucleus PCA-II

4k, Wilkinson99 h 29

1 500-

10 000 240 EM1, IM, LTE

1b As above As above 170 h 47 10 000 240,80 EM1, IM, LTE

2a As aboveCanberra 8713

8k, SUCAPP99 h 30

1 500-

10 000 240 EM1, IM, LTE


3aOrtec GEM35-plus,

47%,1.8 keV

Ortec

DSPEC-plus106 h 34

1 500-

10 000 160 EM2, IM, LTE


Note: SUCAPP is successive approximation; TDM is total duration of measurements; NP is number of points; SMI is single measurement

interval; ND is nominal distance of source-detector，mm; Td is dead-time; EM is external source monitor, 1 for 54Mn，2 for 60Co; IM is

internal source monitor; LTE is life time extension.

In 1a and 2a, both external source monitor 54Mn (834 keV) and LTE methods were used for dead-time corrections. When 724 and 756 keV peaks of 95Zr have satisfactory statistics (about 80 h after the beginning of measurements), 95Zr participated in the dead-time corrections as internal monitors. In 1b and 2b, after the series measurements at 240 mm position for 100 h, the sample was lowered to 80 mm position and the series measurements continued for another 70 h. In 3a and 3b, similar measurement procedure was used except that 60Co, instead of 54Mn, was used as an external source monitor. A least square fitting on the natural logarithm of IM- or EM- or LTE- normalized 658/743 keV peak counting rates at the beginning moment of each counting interval versus decay time was used to obtain the half-life of 97Zr.

Six sets of 97Zr half-life data from three systems and two measurement durations using internal and external source monitors are listed on the left side of Table 2. The unweighted mean of the six, 16.755 h, is adopted as the final result. The standard deviation is 0.013 h. Six sets of 97Zr half-life values by using LTE dead-time corrections are also given on the right side of Table 2, for reference.


Table2 Results of 97Zr half-life

NoEM/IM Td correction LTE Td correction

658 keV 743 keV Peak Av. 658 keV 743 keV Peak Av.

1a 16.772 16.76 16.766 16.916 16.904 16.91

1b 16.752 16.75 16.751 16.842 16.841 16.841

2a 16.785 16.768 16.776 16.913 16.895 16.904

2b 16.754 16.728 16.741 16.832 16.807 16.82

3a 16.765 16.74 16.752 16.772 16.748 16.76

3b 16.757 16.727 16.742 16.758 16.733 16.745

The simplified decay scheme of 97Zr-97Nbm-97Nb is shown in Fig. 1. After irradiation for 1.5 h and decay for 24 h, the intensities of 658 and 743 keV peaks reach complete equilibrium with 97Zr. The half-life of 97Zr is therefore determined by the time-series measurements of these two peaks.

Fig. 1 Simplified decay scheme of 97Zr-97Nbm-97Nb

The resulting value of 97Zr half-life, (16.7550.013) h, is in excellent agreement with the literature value of (16.7440.011) h.

IM/EM normalized 658/743 keV peak counting rates, decay-corrected with the half-life of 16.755 h to the very beginning moment of the series measurements, are plotted against decay time, as shown in Fig. 2. More than 98% of total points (230 out of 234) fall within 1% variation interval and 100% points fall within 2% variation interval, confirming the reliability of the result.

Although measurements 1b, 2b, and 3b have the advantage of longer total duration of measurements compared with 1a, 2a, and 3a, the change in counting position and the relatively small 658/743 keV peaks superimposing on the high continuum of 724/756 keV -rays may introduce additional non-statistic (as well as statistic) uncertainties in the second half of 1b, 2b and 3b measurements. Therefore the unweighted average of all the six data is adopted as the result of present work. As shown in Table 3, the reproducibility and consistency of 658 and 743 keV efficiency ratios between two counting positions used in 1b, 2b, and 3b indicate the reliability of the two counting position relay method.


Fig. 2 Decay-corrected (658+743) keV peak counting rate vs decay time

Table 3 Normalized counting rate ratios between two geometries

No.PCA-II, 4K Canberra 8713, 8K Ortec DSPEC-Plus, 8K

658 keV 743 keV 658 keV 743 keV 658 keV 743 keV

1 8.412 8.374 8.413 8.402 13.442 13.381

2 8.441 8.422 8.456 8.454 13.414 13.431

3 8.386 8.392 8.367 8.489 13.574 13.508

4 8.441 8.398 8.453 8.453 13.500 13.479

5 8.410 8.436 8.362 8.462 13.471 13.470

6 8.439 8.423 8.382 8.416 13.501 13.363

7 8.382 8.354 8.389 8.413 13.381 13.512

8 8.451 8.399 8.393 8.461 13.431 13.271

AV 8.420 8.400 8.402 8.444 13.464 13.427

RSD, % 0.3 0.3 0.4 0.4 0.5 0.6

As shown in Table 2, the half-life values obtained by using IM/EM on three systems representing three generations of pulse processing strategies, Wilkinson (constant-current discharge), successive approximation, and digital DSPEC-Plus, agree with each other within uncertainty limits, further consolidating the result.


71 Study of Surface Loss Process on a Simulated Stainless Steel Material by Thin Layer Activation

HUANG dong-hui, WANG Ping-sheng, TIAN Wei-zhi, NI Bang-fa, LIU Cun-xiong, ZHANG Gui-ying

Taking the advantages of high sensitivity, non-destruction, and the capability of on-line measurement at favorable conditions, thin layer activation (TLA) is recognized as a method of choice in the study on surface loss processes of various materials. In this work, a stainless steel material was studied by TLA with two tracers produced via reactions on Fe and Cr using 9 MeV protons. The advantages of TLA for materials consisting of multiple elements are discussed.

1 Experimental1.1 Sample preparation

The calibration sample package consisting of about 1 cm×1 cm in area and 5 μm in thickness each of 40 stainless steel slices was packed by aluminium foil. The thickness of slices was determined by accurately measuring the area and weight. A test stainless steel sample of about 1 cm×1 cm in area and 5 mm in thickness was prepared for simulated wear study.1.2 Sample activation

The calibration sample package and the test sample were separately activated using 56Fe (p, n)56Co, 52Cr (p, n) 52Mn reactions in the left 10°beam line of HI-13 Tandem Accelerator at CIAE. The energy of the incident protons was 9 MeV and the beam current was about 1 A. The integrals charge for the calibration sample package and the test sample were each 4 000 C.1.3 Establishment of calibration function

After activation, the calibration sample package was unpacked. Each slice was measured for the specific peak counting rates of the tracer nuclides 56Co and 52Mn. The calibration function of loss thickness vs relative residual radioactivity was established.1.4 Simulated wear experiment

For simulated wear study, a home-made grinding machine was built. The activated test stainless steel sample was step-wisely grinded with about 5-10 μm for each grinding. Both the weight of the sample and the counting rates of the specific gamma-rays of the two tracers were taken before and after each grinding.1.5 The measurement of radiotracers

The measurement system consists of a HPGe detector (energy resolution is 1.9 keV, the relative efficiency is 47%) and an Ortec DESPEC-PLUS Unit. The full energy peaks 846.7 keV for 56Co and 743 keV for 52Mn for all sample weighs were measured at a fixed (or convertible) geometry.

The counting rate measurement of the γ-rays of 847, 743 keV from two main components (Fe and Cr) of activated stainless-steel samples was performed. The calibration curve, which is the relation between thickness loss and residual radioactivity, was obtained as shown in Fig. 1.

In simulated experiment, the relative deviation between the wear thickness values from direct weighing and TLA using the established calibration curve is well within 5%-10%, an uncertainty acceptable for most applications, as shown in Table 1.


Fig. 1 Calibration curve of the stainless steel

◆—744 keV peak；■—847 keV peak

For the wear measurement of materials with multiple components, TLA is not only applicable but also advantageous in that the wear thickness values obtained from different tracers offer additional reliability by crosscheck of each other, and the differences in half-life and depth profile of different tracers may provide the users with greater flexibility in the interested range of wear thickness and the duration of wear study.

Table 1 Comparison results between direct weighing and TLA method

No.Thickness from

weighing

56Fe (n,γ) 56Co 52Cr (n, γ) 52Mn

Activity left for

847 keV peak

Thickness from

curve

Relative

deviation/ %

Activity left for

744 keV peak

Thickness

from curve

Relative

deviation / %

1 0.000 100.00 0.00 0.00 100.00 0 0.00

2 22.413 57.42 21.35 4.74 48.90 20.31 9.38

3 33.074 39.93 31.92 3.49 29.56 31.25 5.52

4 40.671 26.86 41.92 3.07 15.83 41.54 2.14

5 49.189 19.10 48.98 0.42 8.77 48.81 0.77

6 55.315 10.85 58.31 5.42 3.57 56.69 2.49

72 Study on Real-Time Wear Measurement of Piston-Ring and Cylinder-Bore in an Engine Using Thin Layer Activation Method

HUANG Dong-hui, WANG Ping-sheng, TIAN Wei-zhi, NI Bang-fa, ZHANG Gui-ying, LIU Cun-xiong


Wear of the piston-ring and the cylinder-bore in a diesel engine was simultaneously measured，for the first time in our country， by using thin layer activation method. The feasibility of the on-line measurement method was verified.

1 Experiments1.1 Activation of piston-ring and cylinder-bore

The piston-ring and cylinder-bore of a diesel engine were activated using 56Fe (p, n) 56Co, 52Cr (p, n) 52Mn reactions in the left 100 beam line of HI-13 Tandem Accelerator at CIAE. The energy of the incident protons is 9 MeV and the beam current is about 0.7 A. The integral charge of the piston-ring and cylinder-bore is 20 000 and 3 000 C, respectively, the total radioactivities produced are 750 kBq (20.3 µCi) and 722 kBq (19.5 µCi) for 56Co and 52Mn, respectively.

There are two activation spots in each of the piston-ring and cylinder-bore. Another set of piston-ring and cylinder-bore was activated at the same conditions for calibration.1.2 Engine and accessorial facilities for experiment

The engine used in this work is a ZS1105 diesel engine from market. The rating power is 13.3 kW, and the rotation speed is 2 200 r/min. The accessorial facilities for the experiment include an electrical generator as load, an oil pump for oil circulation, an engine control panel consisting of a power meter, a current meter, a voltage meter, etc. 1.3 Experiment system

The experiment system consists of a 0.23 L lubrication oil cup on the top of a HPGe detector. The radioisotopes of 56Co and 52Mn in the oil cup were determined by a gamma-ray spectrometer consisting of a Canberra HPGe detector (relative efficiency 25%, energy resolution 3.0) and an Ortect DESPEC-Plus Digit Unit. Fig.1 is a schematic diagram of the experiment system.

Fig. 1 Experiment system

1.4 Real-time determination for wear of piston-ring and cylinder bore by TLA During experimental operation, the full energy peaks of the radiotraces 56Co(half life is 77.23 days,

the energy of γ-ray is 846.8 keV(99.9%)) and 52Mn(half life is 5.59 days, the energy of γ-ray is 744.2 keV(90.0%)) were measured continuously with each counting interval of 300 s. The real-time wear measurement for the first piston-ring and cylinder-bore was carried out at 5 different operation conditions: low speed without load (I), middle speed without load (II), low speed with full load (III), high speed with


full load (IV) and engine shutdown while oil circulating (V). The basic engine operation parameters are shown in Table 1.

Table 1 Basic engine operation parameters

Operation

stateLoad Power/W Voltage/V Current/A

Rotation speed/

(r•min－1)Oil Temp./℃ Cooling water Temp./℃

I 0 0 160 0 1 100 57 67

II 0 0 380 0 1 700 62 78

III Full 4 900 280 17.5 1 460 73 62

IV Full 5 700 352 16.2 1 770 50 40

V 0 0 0 0 0 50 40

2 ResultsTables 2 and 3 show the results for the wear of the piston-ring and cylinder-bore in the five operation

conditions mentioned above.

Table 2 Wear of piston-ringState Time/h Radioactivity loss /% Accumulated wear/µm Wear in interval/µm Wear rate/(µm/h)

I 4.0 0.000 0.000 0.000 0.000

II 2.0 0.882 0.531 0.531 0.000

III 2.5 34.224 28.505 27.974 11.190

IV 2.5 64.393 59.824 31.319 12.528

V 0.5 64.652 59.824 0.000 0.000

Table 3 Wear of cylinder-boreState　 Time/h Radioactivity loss/% Accumulated wear/µm Wear in interval/µm Wear rate/(µm/h)

I 4.0 0.103 0.044 0.044 0.000

II 2.0 0.170 0.073 0.029 0.000

III 2.5 1.030 0.443 0.370 0.148

IV 2.5 2.510 1.079 0.636 0.255

V 0.5 2.510 1.079 0.000 0.000

3 DiscussionIn this work, charged particle induced thin layer activation was used for both the piston-ring and the

cylinder-bore. Compared with the reactor neutron bulk activation (98Mo (n,γ) 99Mo) for piston-ring used in the similar study[1] by Schneider of US General Motor research and development center, the total radiation dose is largely reduced. The total radioactivity in Schneider’s work is 300 µCi, compared to 19 µCi in this work.

The 9 MeV energy of incident protons used for the two activation reactions enables > 90% of the radiotracers distributed in the interested thickness range (80-100 µm), and this proton energy is also easily available for HI-13 tandem. The beam current of 0.7 µA is a good compromise between available beam time and the integrity of the activated material.

One of the preconditions of TLA method is that the wear debris should be homogeneously distributed


in the lubrication oil. The high speed lubrication oil pumping (10 s circulation rate) used in this work satisfies this precondition. Besides, instead of campaniform cup used by Schneider, a flat-bottom cup was used to avoid the “dead volume” during oil circulation, though there may be some sacrifice in the solid angle.

The minimum detectable wear thicknesses are 9 and 100 nm for cylinder-bore and piston-ring, respectively, based on the background counts at interest peak regions.

4 ConclusionsSimultaneous and real-time wear measurement of the piston-ring and cylinder-bore of a diesel engine

was studied, for the first time in our country, using thin layer activation (TLA) method at five different operation conditions. The feasibility of TLA method is verified.

Compared with the previous work by Schneider, some improvements are achieved: 1) Charged particle thin layer activation, instead of reactor neutron bulk activation, was used for the piston ring, resulting in 100 times’ lower gross radiation dose while keeping the same sensitivity; 2) The energy and current of the proton beam used in this work ensures a good compromise between acceptable beam time and the integrity of the activated material; 3) The use of the high speed oil pumping and the flat-bottom cup ensures the satisfaction of the two important preconditions, homogeneous distribution of wear debris in the lubrication oil and “dead volume”-free during circulation.

As first experiment, a very strict dose control was adopted in this work. After assembly, the radiation dose in the position closest to the engine was measured to be less than 15 µGy/h. If the total tracer activity increases by 10 times, the dose will be at most 150 µGy/h (allowing 5 h operation at nearest position, more than enough). A 10 time efficiency increase is also easily achievable by using larger detector and oil cup. Therefore, there is at least a room for 100 time improvement in sensitivity compared to this work, that makes the minimum detectable wear being 0.1 and 1 nm for cylinder-bore and piston-ring, respectively. The method can therefore be used for on-line wear measurement of engines with better quality piston-ring and cylinder-bore (smaller wear rate) and larger oil tank (smaller fraction of oil in measuring cup).

Reference:[1] ERIC W S, DANIELl H B. Radiotracer method for measuring real-time piston-ring and cylinder-bore wear in spark-

ignition engines. Nuclear Instruments and Methods in Physics Research, A559-563, 2003.

73 Study on Sources of PM2.5 Inhalable Air Particles From Liangxiang by PIXE

ZHANG Gui-ying, NI Bang-fa, TIAN Wei-zhi, David D. Cohen1, Eduard Stelcer1, Olga Hawas1,WANG Ping-sheng, HUANG Dong-hui, LIU Cun-xiong, LI De-hong

（1 Australia Nuclear Science and Technique Organization）

Fifteen PM 2.5 aerosol samples collected during 27 January to 11 March 2005 from a Middle School in Fangshan District, Beijing, have been analyzed using PIXE in Australia Nuclear Science and Technique Organization. Multielements, including those hardly available by INAA, such as Si, S and Pb, were determined. Elemental data were interpreted using statistic methods.


The contents of black carbon in these aerosol samples were also determined to be 3.3 µg/m 3 and 6.7 µg/m3 for median and maximum values, respectively, by using a “Smokestain Reflectmeter”. Black carbon content was typically (10.93.6)% of the total average PM 2.5 mass, indicating that black carbon was one of the major contamination sources.

Trace elements, including F, Na, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe, Co, Ni, Cu, Zn, Br and Pb, were determined with detection limits close to or below 1 ng/m3. By using mass re-construction technique, the average PM2.5 percentage composition by weight was estimated to be around (19.65.7)% ammonium sulfate, (20.58.3)% soil, (4.91.2)% salinity and (0.9 0.8)% smoke.

The source fingerprinting of major events at a given site can be achieved quite easily through time series plots of the volume concentrations of elements determined. Fig. 1 shows K and S volume concentrations measured during the three-month period from 27 January to 11 March 2005 at a Middle School in Fangshan District, Beijing. The highest peaks at February 16, the nearest sampling day of Chinese Spring Festival, clearly attributed to firework display. The K peak on February 16 is 1 694 ng/m 3, 7.2 times higher than the peak on February 7. The similar trend can be observed in the time-series data for S. Figure 2 shows there are strong correlations between elements associated with soil.

Fig. 1 Time series plot of PM2.5 nssK and nssS

◆—nssK；■—nssS


Fig. 2 Correlation plot for PM2.5 soil elements

Two dimensional element to element plots can also be used to identify possible sources. For example, a plot of Zn against Pb and a plot of Br against Pb (showed in Fig. 3 and Fig. 4) shows a positive correlation in low-concentration region. This correlation may reflect there is still gasoline associated Pb. Fig.5 shows two distinct sources associated with K and Black Carbon. The possible sources may be biomass combustion, coal burning, motor vehicle or firework.

Fig. 3 Correlation plot for PM2.5 Zn vs Pb

Fig. 4 Correlation plot for PM2.5 Br vs Pb


Fig. 5 Correlation plot for PM2.5 K Br vs BC

74 Study on Properties of Solid Material Surface Modified by Nuclear Tracks

LIU Cun xiong, NI Bang-fa, XIAO Cai-jin, TIAN Wei-zhi, WANG Ping-sheng, ZHANG Gui-ying, HUANG Dong-hui, LI De-hong, LI Xue-zhen, SHEN Li, YANG Wei-tao

Study on peculiar properties of material surfaces modified by nuclear tracks was originated from the

solid state nuclear track detection techniques developed half century ago for recording and investigating

the properties of various nuclear particles. In this work, the principles of the nuclear tracks on solid

materials were used to study on insulating and optical characteristics of some nuclear track modified solid

materials. Some preliminary conclusions have been achieved.

The insulating materials were used in experiments, because only on insulating materials can nuclear

tracks be recorded. Polyester, polycarbonate and mica were selected as test samples. Polyester and

polycarbonate belong to organic macromolecule polymer, mica is inorganic. The sensitivity to record

nuclear tracks and the method to develop the tracks are all different for polymer and mica. Sensitivity of

polymer is much greater than mica. Alkaline solution was used to etch samples to make tracks developed,

for mica strong acid is appropriate. In our experiments sodium hydroxide and hydrofluoric acid were

selected as the etching solution for polymers and mica, respectively. The etching conditions (density of

tracks, concentration and temperature of etching solution, time for etching samples) were various to meet

different requirements on the diameter, the depth (and less importantly, the shape) of the tracks on sample

surfaces. As a result, properties of nuclear track modified sample surface were changed. And it varied

with different diameter and depth. The electric resistance and optical parameters such as reflectivity,

transmission were measured. Figure 1 shows two SEM pictures for polyester surface. Figure 1a shows

excellent anti-metal contamination and anti-reflect properties. That is because the density of the nuclear

tracks is much higher than that in the right picture. Actually the tracks are even largely linked and


overlapped with each other. Figure 2 shows little anti-metal contamination and anti-reflect properties.

Fig. 1 The SEM of different polyesters

a, b shows different polyesters

Fig. 2 The SEM of mica

Figure 2 is a SEM graph for mica. Compared to Fig. 1, the etched nuclear tracks on mica were

rhombus (the rhombus was not flat), unlike the conical or cylindrical tracks on polyester. Mica is made of

many layers. The etching solution might stay between layer and layer. That may lead to stair-like surface.

The ability of anti-metal contamination was decreased greatly. And anti-reflectivity ability is complicated

because of desquamation. So mica isn’t suitable for studying anti-metal contamination and anti-reflect

properties through surface modification by nuclear tracks.

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