exploration of nuclear structure and decay of heaviest ......decay spectroscopy of she nuclear...
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Fritz Peter HeßbergerGSI – Helmholtzzentrum für Schwerionenforschung mbH,
D-64291 Darmstadt, GermanyHelmholtz – Institut Mainz, D-55099 Mainz, Germany
NN2015 12th International Conference on Nucleus – Nucleus Collisions
Catania, Italy21 – 26 June 2015
Version 18. 6. 2015
Exploration of Nuclear Structure and Decayof Heaviest Elements at GSI - SHIP
The Strong Force
Quark – Gluon - Plasma Formation and development of stars Development of the universe Synthesis of the chemical elements Structure of the atomic nuclei
One of the four basic interactions,playing among others an essential role for
The Strong Force
146 148 150 152 154 1560,0
0,5
1,0
1,5
2,0
Neutron shell N = 152
Shell strength parameter 2nof nobelium isotopes ( Z = 102)
SLy4 - prediction
exp. values
2n
/ MeV
Neutron Number
0
200
400
600
0
200
400
600
1/2-[521]
7/2-[514]
experiment
0+x30+x20+x1
294+x3253+x2
210+x1
E* /
keV
E* /
keV
7/2+[633]
3/2-[521]
253Es251Es249Es247Es245Es243Es
1/2-[521]
7/2+[633]
7/2-[514]
3/2-[521]
HFB - SLy4 (Chatillon et al. EPJ A30, 397 (2006))
Physics Motivation for Synthesis and NuclearStructure Investigations of SHE
Why synthesis and nuclear structure investigations ?
Atomic nucleus is quantum mechanical ensemble of nucleons (p, n)
Properties determined by ‚fundamental‘ interactions- nucleon – nucleon interaction- Coulomb interaction- spin – orbit interaction- ….
Understanding decay properties and structure of nuclei is thus essential for understanding ‚fundamental‘ interactions
Superheavy nuclei (SHE) are a specific class of exotic nuclei ensembles of ‚extremely‘ large numbers of protons and neutrons despite of high density of nuclear levels ‚gaps‘ between single particle
states occur at certain numbers of Z and N indicating ‚shell closures‘ no macroscopic (‚collective‘) fission barrier any more, stability against
prompt disruption due to ‚shell effects‘; Bf depends on single particle levels shell structure determines nuclear mass excess determines Q-values forα- and β- decay
Physics Motivation for Synthesis and NuclearStructure Investigations of SHE
Understanding nuclear structure of SHE is
essential for understanding their
properties and stability
i.e. the ´limits of our world´
Topic Questions Are there proton and neutron shells at all ?
How strong are they ?Where are they located ?
140 145 150 155 160 165 170 175 180 185 190
100
105
110
115
120
125
neutron number
prot
on n
umbe
r
<1
<104
<104 <10-4
<1
<1<1
>104
<10-4
<10-8
N=184N=162
Z=114
Z=108
-decay
-decay
SF expected decay modes and halflives
Expected Decay Modes and Halflives of SHE
Nuclear Structure
Synthesis
Velocity separator SHIP
SHIPSeparation time: 1 – 2 μsTransmission: 20 – 50 %Background: 10 – 50 HzDet. E. resolution: 18 – 25 keVDet. Pos. resolution: 150 μm Dead time: 25 μs
Decay Spectroscopy of SHE
Nuclear structure investigations require a large amount of events, but production rates of SHE are low (ca. 240 /d/nb)
Nuclear structure of odd-A even Z nuclei is similar along isotone line
Nuclear structure of odd-A even Z nuclei is similar alongisotope line
Study of systematics of (low lying) Nilsson levels inodd A nuclei
Decay schemes of the N=153 Isotones 255No, 257Rf, 259Sg
199.
9 (M
2+E3
)
163.
3 (M
1)
257Rf255No
251Fm
(35+x) (8255 (3 %)
(8290 (5 %)
(3/2+ ?) 392354
200
353.
8(E1
)19
4.5
(M1)
166.
8 (M
1)
7941 (0.4 %)
7742 (19%)
7903 (11 %)
(7/2+[624])
21 s
(1/2+[620])
(5/2+[622])
(9/2-[734])
(1/2+[631])
192.
1 (E
2)
358.
3 (E
2)
0
394
558
(1/2+[620])
8095 (58 %)
(7893 4 %)
(8962)
9021(8950)
(8680)
8778
(8510)(8450)
24 s
5.7 s4.9 s
510
450
258
16716
7(M
2+E3
)
62
0
91(M
1)28
3 (E
2)
(1/2+[620])?
(3/2+)
(3/2+,5/2+,7/2+)
(11/2-)
(9/2-[734])
(5/2+[622])
(1/2+[620])
(11/2-[725])
(9/2-[734])
(11/2-[725])
40 s
(1/2+[620])?
253No 255Rf
9240
9545
9702
9610
9035
594
(1/2+[620])
(11/2-[725])
259Sg
594
(462)
ca.150
0
411 ms
254 ms
(5/2+[622])
F.P. Heßberger et al. Z.Phys. A 359,415 (1997)B. Streicher et al. EPJ A 45, 275 (2010)
F.P. Heßberger et al. EPJ A29,165 (2006) S. Antalic et al. EPJ A 51:41 (2015)
Decay Study of 257Rf
direct production 208Pb(50Ti,n)257Rf(F.P. Heßberger et al. Z.Phys. 359, 415 (1997))
production by α-decay of 261Sg(B. Streicher et al. EPJA 45,275 (2010))
(data scaled to same intensity in theregion E = 8.7-8.8 MeV)
real effect ??
(T1/2 = 4.9 s) (T1/2 = 5.7 s)
Decay Study of 257Rf
SHIP – Exp. 2014
Decay Study of 257Rf
prand < 10-6
Decay Study of 257Rf
coincidence not observed in production by α-decay of 261Sg
assignment to 257Lr unlikely due to α-α-correlation to 253No
certainly related to decay of 257mRf
Eα+Eγ = 8.86 MeV, but Eα(257mRf) = 9.03 MeV suggests population of a level at E* ≈ 170 keV (5/2+ isomer !!!) cannot be 11/2-(257mRf) 11/2-(253No) transition; prefers M1
transition to 9/2- gs. and not E3 transition to 5/2+ isomer α-transition only slightly hindered (HF ≈5-10); no parity change,
no spin-flip
x
x
x
xxxx
xx
Decay Study of 257Rf – expected levels in 253No
Nilsson-Levels in N=151 Isotonesexperimentt Z.H. Zhang et al. PRC 85, 014423
(2012)M. Bender et al. NPA 723, 356 (2003),and priv. comm. 2015
M. Asai et al. PRC 83, 014315 (2011)A. Parkhomenko, A. Sobiczewski,Acta. Phys. Pol. B36, 3115 (2005)
S. Cwiok et al. NPA 573, 356 (1994)
Ident. 11/2-and confirm 7/2-
in 253No
Nilsson-Levels in N=153 Isotonesexperimentt
Z.H. Zhang et al. PRC 85, 014423(2012)
M. Bender et al. NPA 723, 356 (2003),and priv. comm. 2015
S. Cwiok et al. NPA 573, 356 (1994)A. Parkhomenko, A. Sobiczewski,Acta. Phys. Pol. B36, 3115 (2005)
Ident. 11/2-in 255No
156 158 160 162 164 166 168 170 172 174 176 178 180102
104
106
108
110
112
114
116
118
118-294
117-294117-293
Lv-293Lv-292Lv-291Lv-290
115-290115-289115-288115-287
Fl-289Fl-288Fl-287Fl-286Fl-285
Cn-285Cn-284Cn-283Cn-282Cn-281
113-283113-282 113-284 113-285 113-286
Rg-282Rg-281Rg-280Rg-279Rg-278
Ds-281Ds-279Ds-277
Mt-278Mt-277Mt-276Mt-275Mt-274
Hs-277Hs-275Hs-273
Bh-274Bh-272Bh-271Bh-270
Sg-271Sg-269
Db-270Db-268Db-266Db-267
Rf-267Rf-265
Lr-266
StrukturSWK/Abbildungen/NukaSHE
Neutron Number
Pro
ton
Num
ber
Z – Identification of SHE α-chains terminated by sf sf of o-o – nuclei strongly hindered maybe no sf of o-o nucleus observed;
but sf of e-e daughter af EC EC is a ‚certain‘ source for K-X-rays Z – identification by delayed
coincidences betweenK – X-rays and sf
test-case: 258Db
Predict. SF - halflives266Rf: 23s268Rf: 1.4s270Rf: 20 ms
sf (
EC (
EC (
EC(?) (
254Lr
258Db
254No
258Rf18 s
1.9 s | 4.3 s
15 ms
55 s
_
Direct Prove of EC of 258Db
From delayed coincidencesT1/2(sf) = 14.5 ± 5.2 ms
sf (
EC (
EC (
EC(?) (
254Lr
258Db
254No
258Rf18 s
1.9 s | 4.3 s
15 ms
55 s
_
258Rf:Eα= 9.05±0.03 MeV, bα = 0.31 ± 0.11 (J. Gates et al. PRC 77, 034603 (2008))Eα= 9.07±0.02 MeV, bα = (0.07 +0.08/-0.04, preliminary ) (this work)
Alpha – decay branch 258Rf
Proof of EC Decay of 257Rf
configuration• stop detector: 1 DSSD (6060 strips)• box detectors: 4 SSSD (32 strips)• overall particle - γ-efficiency ≈ 40%
chamber• compact (overall length 35 cm)• Al-cap with thin window (1,5 mm)• compatible due to 150 mm standard flange• electronics partly integrated (vacuum)
DSSD• integrated cooling (Cu-frame) and
connection (flex-PCB)• 6060 strips/mm (pitch 1 mm)• 300 µm
configuration• stop detector: 1 DSSD (6060 strips)• box detectors: 4 SSSD (32 strips)• overall particle - γ-efficiency ≈ 40%
chamber• compact (overall length 35 cm)• Al-cap with thin window (1,5 mm)• compatible due to 150 mm standard flange• electronics partly integrated (vacuum)
DSSD• integrated cooling (Cu-frame) and
connection (flex-PCB)• 6060 strips/mm (pitch 1 mm)• 300 µm
Enhanced Focal Plane Detector Set-up forSHE Spectroscopy
D. Ackermann, J. Maurer, M. Vostinar,J. Piot, N. Kurz,P. Wieczorek,J. HoffmannF.P. Heßberger et al.
Enhanced Focal Plane Detector Set-up forSHE Spectroscopy
First on-line test at LISE – Wienfilter GANIL, november 201440Ar (4.66 AMeV) + 174Yb 209,210Ra
energy resolution≈ 20 keV (FWHM)
DSSD – analog signal processing
209,210RaFWHM = 45 keV
single trace
energy / channels
Enhanced Focal Plane Detector Set-up forSHE Spectroscopy
Digital signal processing FEBEX + conventional PADSSD, Ge-detectors, .....● fast timing ● deadtime free ● pulse shape analysis options
Conclusions
Decay spectroscopy and ground state mass measurement are powerful toolsto investigate nuclear structure of SHE in terms of ordering of nuclear levels energy systematics of Nilsson levels identification of neutron (and proton) shell determination of shell strenghts the stability of (multi) quasi-particle states
Measuring X-rays from EC in delayed coincidence with the decay (α, sf) isprobably an alternative method for Z – identification of SHN.
population of excited levels in daughter nuclei by EC decay is an additionalsource for nuclear structure information
Future Goals: identification of ‚missing‘ levels relevant for strength and location of the
‚SHE – shells‘ at Z ≤ 106 detailed nuclear structure investigations at Z > 106 ‚more‘ detailed study of K – isomers at Z = 100 - 110
SHIP – SHE Nuclear Structure Collaboration (Spokesman: F.P. Heßberger)
GSI, DarmstadtM.Block, S.Heinz, F.P.H., B.Kindler, I.Kojouharov, J.Khuyagbaatar, B.Lommel
Helmholtz Institut MainzA. Mistry, M. Laatiaoui, J. Even (now at TRIUMF, Vancouver)
Comenius University Bratislava, SlovakiaS. Antalic, B. Andel, Z.Kalininova (now at JINR, Dubna), S.Saro (deceased)
GANIL, Caen, FranceD. Ackermann, H. Savajol, J. Piot, M. Vostinar
JAEA Tokai, JapanK. Nishio
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