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K. Asahi Tokyo Institute of Technology (Tokyo Tech)
Nuclear structure studies with polarized radioactive beams
The 18th International Spin Physics Symposium (SPIN2008) 6 - 11 Oct. 2008, Univ. of Virginia, Charlottesville, Virginia, USA.
OUTLINE:
1. Spin in Low-energy Nuclear Structure Physics
2. History of the Spin-polarized/Aligned Radioactive Beams (RIB)
3. Nuclear Moment Measurements with Polarized/Aligned RIB
4. Recent Results on n-rich Al isotopes and the Island of Inversion
Neutron number N
Pro
ton
nu
mb
er Z
Chart of Nuclei
Nucleus: Many-body system of fermions of two types
(Nucleus along the stability line)
●Bunching of the single-particle levels
⇒ determines the Nuclear Structure
Nucleus: Many-body system of fermions of two types
2
16
6
increase of N/Z(Nucleus along the stability line) (Neutron-rich nucleus)
New magic numbers ??
●Bunching of the single-particle levels
⇒ determines the Nuclear Structure
In fact, the shell does evolve, ..... due to the tensor force.
is
・ attractive for j> - j<', j< - j>'
・ repulsive for j> - j>', j< - j<'
[Otsuka et al., PRL 95 (05) 232502]
[Otsuka et al., PRL 97 (06) 162501]● Monopole energy of the tensor interaction
T, '
2 1 ' '
2 1JTJ
j j
J
J jj V jjV
J
proton neutron
j'>
j'<
j>
j<
is
・ attractive for j> - j<', j< - j>'
・ repulsive for j> - j>', j< - j<'
[Otsuka et al., PRL 95 (05) 232502]
[Otsuka et al., PRL 97 (06) 162501]● Monopole energy of the tensor interaction
T, '
2 1 ' '
2 1JTJ
j j
J
J jj V jjV
J
proton neutron
j'>
j'<
j>
j<
proton neutron
j'>
j'<
j>
j<
In fact, the shell does evolve, ..... due to the tensor force.
Thus, the single-particle orbits may migrate leading to a possible change in shell structure.
Note that the s.p. orbits are characterized by the angular momentum j.
Also,
decoupling of neutron from the core
+++
eeff(n) 0.5
(in a normal nucleus)
eeff(n) 0 ??
core
(in a n-rich nucleus)
Such an effect can be detected through measurement of electric quadrupole moments Q associated with nuclear spin.
ebare(n) = 0
Thus, the spin plays
vital roles in structural change of nuclei
towards far from stability
Observation of spin-alignment in projectile fragments
RIKEN-GANIL collab.
(at LISE/GANIL, 1987)
14B
18O (60 MeV/u) 14B fragment
9Be target
2
1
0
6.094 MeV
Target
Projectile Fragment
Pfrag = Mv0 P'part
P'part = p'i
LFrag = R P'Part
PLB 251, 499 (1990)
Angular momentum introduced in a projectile fragmentin the intermediate-energy PF reaction
p'iv0
R
-- Angular momentum introduced in the fragment
(internal Fermi motion)
Spin polarization found in RI beams from PF reaction
z∥ ki kf
p||
Expected spin alignment in the 14B fragment
Goldhaber distribution
Result of the RIKEN-GANIL collab. experiment:
Alignment result at GANIL '87
Expected spin alignment in the 14B fragment
Goldhaber distribution
Result of the RIKEN-GANIL collab. experiment:
Polarization - at RIKEN, '90
Analyzer
L
43mSc (19/2) TD-PAD
Spin Rotation of aligned fragments, - at FRS/GSI, '93
Z. Phys. 350, 215 (1994)
B0 = 0.265 T
B0 = 0.265 T
RIPS/RIKEN, present
RIPS
K=540 RIKEN Ring Cyclotron
Isotope separationmagnetic analysis (A/Z)
+momentum-loss analysis (A2.5/Z1.5)
Production of spin polarizationscattering-angle selection
+momentum analysis
RIPS
Detector
Large-Z target
Detector
Small-Z target
near-side trajectory far-side trajectory
40AMeV
Au Nb Nb AlAu
70AMeV 110AMeV 70AMeV 70AMeV
H. Okuno et al., PL B 335, 29 (1994)
Fragmentation-induced spin polarization
● The kinematical model reproduce quite well the observed behavior of polarization P as a function of momentum and target Z-number.
● However, the observed ‥‥ magnitudes of P are by ~ 1/4 smaller than predicted.
•g-Factors measured at RIKEN–Boron isotopes : 14B, 15B, 17B–Carbon isotopes : 9C, 15C, 17C–Nitrogen isotopes : 17N, 18N, 19N–Oxygen isotopes : 13O–Fluorine isotopes : 21F–Aluminum isotopes : 23Al, 30Al, 32Al
•Q-moments measured at RIKEN–Boron isotopes : 14B, 15B, 17B–Nitrogen isotopes : 18N–Oxygen isotopes : 13O–Magnesium isotopes : 23Mg–Aluminum isotopes : 31Al, 32Al
TITech / RIKEN
Osaka / RIKEN
Spin-parity assignment
Reduction of E2 effective charges
Effect of n-excess
Spherical or deformed?
Nuclear moments measured at RIPS/RIKEN
●With spin-polarized fragment beams ....
<> from IS
●Reduction of effective charges
●Reduction of effective charges
pol 1n,p 0 1 '
0
2
' 2
1( ', ) 1
4 2
where
3/5
'
z z j j
j j
Z V N Z N Ze j j
A V A A
R
j r j
j'j ≈ 0.5 (sd orbits)
Thus, effective charges have been shown to reduce significantly as N/Z increases!
This also explains the anomalously hidered E2 transition in 16C reported recently.
GANIL (France)
g-factor: 18N, 32Cl, 31Al, 32Al, 33Al, 34Al, 35Si, ...
Q-moment: 18N, 31Al, 33Al, ...
MSU (U.S.A.)
g-factor: 9C, 35K, 57Cu, ...
Q-moment: 37K, ...
NIRS (Japan)
g-factor: 21F, 27Si, 35Ar, ...
Q-moment: 21F, 23Mg, 27Si, 39Ca, ...
RCNP (Japan)
Snow ball exp. with highly polarized 12B (P ~ 40 % !)
L
Many important works also at ... (a.f.a.I.k.)
●With spin-polarized fragment beams ....
(Matsuo, Furukawa, Shimoda et al.)
A precursor expt. for the recent development, "OROCHI" technique (Optical RI-atom Observation in Condensed Helium as Ion-catcher)
Polarization in pick-up channel(Groh, Mantica et al.)
Present status of the “Island of inversion”(Himpe et al.)
By including (Groh, Mantica et al., 2007)
● Improvements in prediction of P
・ Deorientation effect due to
-ray de-excitation ⇒ ×0.5
・ Out-of -plane acceptance ⇒ ×0.4
・ Angular distribution ⇒ ×0.1
Thus, now the magnitude of polarization that should be obtained in the experiment can be predicted in quite a useful accuracies!
LISE/GANIL (France)
g-factor: 61mFe(9/2+), 69mCu(13/2+), 67mNi(9/2+), ...
Q-moment: 61mFe(9/2+), ...
RISING/GSI (Germany) "g-RISING Campaign"
g-factor: 127mSn(19/2+), ...
●With spin-aligned fragment beams ....
61mFe(9/2+)
(RIKEN-GANIL Collab.)at LISE/GANIL, '87
RIPS/RIKEN '90
(RIKEN-Goettingen-GSI)FRS/GSI, '93
(RIKEN-TIT-GANIL-Leuven)LISE3/GANIL '08
RIBF/RIKEN Present
32Al isomer
E437b collaboration
• RIKEN Nishina Center• Tokyo Tech• Tohoku• KU Leuven• GANIL• Bruyères-le-Châtel• IPN Orsay• Sofia
E437b collaboration
• RIKEN Nishina Center• Tokyo Tech• Tohoku• KU Leuven• GANIL• Bruyères-le-Châtel• IPN Orsay• Sofia
43Sc isomer
(g-RISING Campaign)FRS/GSI, Present
at LISE3/GANIL '08
Recent result: Q-moments for 31,32,33Al
The experiment has been done in collaboration of
H. Ueno, K. A., K. Shimada, T. Nagatomo, A. Yoshimi, Y. Ichikawa, D. Kameda, T. Sugimoto, D. L. Balabanski, J. M. Daugas, K. Flanagan, G. Georgiev, S. Grevy, R. Lozeva, P. Morel, D. Nagae, G. Neyens, F. de Oliveira Santos, L. Perrot, M. De Rydt, C. Stodel, J. C. Thomas, N. Vermeulen, P. Vingerhoets, D. Yordanov, Y. Utsuno(E437b collaboration)
RIKEN, Tokyo Tech, Tohoku, Leuven, GANIL, Sofia, Bruyeres-le-Chatel, IPN Orsay, JAEA
● 31,32Al part: at RIPS/RIKEN
● 33Al part: at GANIL
Nuclear moment studies in the vicinity of the island of inversion
Ne
Mg
Al
Na
F
Si
P
20
Z
N
Island of Inversion Island of Inversion E.K. Warburton, J. A. Becker and B. A. Brown, PRC41(1990)1147.
MCSM with an sdpf model space:Y. Utsuno, et al., Phys. Rev. C 70 (2004) 044307.
20
s1/2
f7/2
d5/2
d3/2
p3/2
f7/2
d3/2
p3/2
Normal sd-shell configuration
d5/2
s1/2
0p0h, spherical 2p2h (intruder), deformed
Na isotopes
s1/2
d5/2
d3/2
f7/2
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
(j<)
d5/2(j>)
T=0 monopole interaction due to tensor force
[Otsuka et al., PRL 95 (05) 232502]
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
T=0 monopole interaction due to tensor force
[Otsuka et al., PRL 95 (05) 232502]
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
T=0 monopole interaction due to tensor force
[Otsuka et al., PRL 95 (05) 232502]
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
T=0 monopole interaction due to tensor force
[Otsuka et al., PRL 95 (05) 232502]
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
T=0 monopole interaction due to tensor force
[Otsuka et al., PRL 95 (05) 232502]
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
T=0 monopole interaction due to tensor force
[Otsuka et al., PRL 95 (05) 232502]
What would be happening in the IOI
00
What would be happening in the IOI
s1/2
d5/2
d3/2
f7/2
-- Gains correlation energies due to near degenerate f7/2 and d3/2 orbits
00
What would be happening in the IOI
[220]1/2
[211]1/2
[202]5/2
[211]3/2
[330]3/2
[200]1/2
-- Gains correlation energies due to near degenerate f7/2 and d3/2 orbits
Question:
Where and how steeply does this quantum phase transition take place as a function of N/Z ratio ?
5/2+
3+ 3+
5/2+
1+
5/2+5/2+
-
mom
ent ( N
)
μ (AAl)
μ(AAl) and Q(AAl)
RIKEN
RIKEN
Q (AAl)
• Qexp stays almost constant at N=14,15, but it becomes smaller at Qexp[32Al] → single-particle(hole)-like structure spherical shape
• Consistent with μ(AAl) - 27 ~ 32Al can be described within the sd- model space → normal configuration
→ 31,32Al are not related to island of inversion
Q
-mom
ent (
e· m
b)
0
50
100
150
200
expUSD
Large-scale shell model & aluminum isotopes
Y. Utsuno et al., PRC 64(2001)011301(R)
33Al
Z=13 is reallya "transitional number"
E. Caurier et al., PRC58(1998)2033
31Al 32Al 33Al 34Al
• decreases from 31Al(30Al)→33Al• E0p0h-E2p2h > 0 for Al isotopes, but similar to Mg, Na, Ne
30
29
31 32 33 34
31Al and 32Al
Primary beam 40Ar
95 AMeV, 40pnA
Nb target Nb, 0.37 g/cm2
Secondary beam 32Al
Emission angle 1.3 – 5.2 deg.
Momentum 12.6 GeV/c ±3 %
Intensity@F2 5 x 103 particle/sec.
Purity 85%
Polarization ~ 0.7 %
RIKEN Projectile fragment separator (RIPS):
B = (mv0 /e) AZ
= 3.6 m)
∝Z2 dEdx
Isotope separation:
Particle identification: • E @ F2 SSD • TOF (F2 PPAC - RRC)
Selected momentum region:
40Ar
LISE/GANIL
Target
Momentum dispersive plane
Achromaticfocal plane
-NMRapparatus
Emission angle: 2±1 deg.
Z
Aselection
5.1
5.2
Z
Aselection
PurityIntensity
36S16+
77.3 A MeV 3.8 e A
33Al
-NMR & -NMR Apparatus
Magnet pole
Plastic scintillators ~100mm I.d.
Spin-polarizedRI Beam
RF Coil~20 mm I.d.~0.1 mT, ~6 MHz
Stopper~22.5x28x1 mm3
-Al2O3 at 130 KSi at room temp.
rays
0.5 T
Production of the polarized 33Al beam
• Momentum analysis with the edge-shape degrader
33AlE
TOF
• Primary beam: 36S, 77.30 A MeV• Target: Be 1212 m • Beam-deflection angle: (2±1)°• Edge-shape degrader: Be, 1068 m• B: 3.1000 Tm• B: 2.9119 Tm
31Mg
32Mg
30Na
28Ne
Purity 75%
Momentum distribution
Gaussian fitting11.87±0.11 GeV/c
Accepted momentum region
Energy levels with eqQ interaction
124
1cos3 axis2
L1,
mc
Qmm
)12(2
3
IIh
eqQQ
h
Bg 0NL
13
128
1cos3 2axis2
0N
IIm
II
eqQmBgE c
m
1, mm
33Al
5.8 – 6.6 MHz
@ ~ 500 mT
33Al (I = 5/2+)m = -5/2
m = -3/2
m = -1/2
m = 1/2
m = 3/2
m = 5/2L
L
L
L
L
-5/2,-3/2
-3/2,-1/2
-1/2,1/2
1/2,3/2
3/2,5/2
0
0
q
B
0
0
q
B
0
0
q
B
Larmor frequency
Quadrupole coupling constant h
eqQ
Adiabatic Fast Passage -Nuclear Magnetic Resonance
0
0-
0+
t
Motion of a moment in a rotation coordinate system(with resonance freq. 0)
Frequency of the oscillating magnetic field B1
staticmagnetic
field
W ( )=1+AP cos A : Asymmetry parameter P : Polarization : Emission angle
NMReffect
(Up/Down)with RF
(Up/Down)w/o RF
(1-AP)/(1+AP)
(1+AP)/(1-AP)= = ~ 1 4AP
Adiabatic Fast Passage NMR
RF: 0=H/Ihe-
e-e-e-
e-e- e-e-e-
e-
-NMR/NQR method
RF signal for Q(33Al) measurement
L
L
L
L
L
-5/2,-3/2
-3/2,-1/2
-1/2,1/2
1/2,3/2
3/2,5/2
0,0 qB 0,0 qB 0,0 qB
= 5.8 – 6.6 MHz
18 ms
Larmor Frequency determination: NMR spectrum
6216.5 ± 6.5 kHzAP = 1.5%
Stopper: SiB0 = 498.8 mT g = 1.635
Preliminary
Q moment measurement: NQR spectrum
= 316 ± 55 kHz
Preliminary
)12(2
3Q
IhI
eqQ
Stopper: -Al2O3
B0 = 498.8 mTq = 67.701019 V/m2
|Q| = 129±22 emb
Comparison of Q moments with shell models
preliminary
Y. Utsuno, private communication
T. Nagatomo et al., to be published
0
10
20
30
40
50
60
70
29 30 31 32 33 34
Mass Number
I = 0g-factor known
Recent μ -measurements in the sd shell
μQ
(Osaka G.)
N=20
E.K. Warburton et al., Phys. Rev. C 41, 1147 (1990)
Island of inversion
GANILISOLDE
RIKEN
M. Keim et al., Eur. Phys. J. A 8, 31 (2000). G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2005)
From recent experiments
G. Huber et al., Phys. Rev. C 18, 2342 (1978)
一連の Al 研究 (RIKEN, GANIL)
Summary
Fragmentation-induced spin polarization/alignment of RI beams has been developed and used for more than ten years.
This technique is nowadays being used at several radioactive beam facilities in the World, providing a powerful means to study the g.s. nuclear moments in the region far from the stability.
Electromagnetic moments provide useful information in nuclear structure physics.
As a recent work with polarized RI beam, preliminary result for the 33Al Q-moment has been presented.
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