Spectroscopy of neutron-rich nuclei
at REX-ISOLDE with MINIBALL
Thorsten Kröll
Physik-Department E12, TU München, Germany
Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik, Garching, Germany
Outline
Milestone of nuclear structure
Shell model  magic numbers
B(E2) values around 132Sn
Do they persist far-off stability?
 Study of radioactive nuclei!!!
• Mean field + residual interactions
- Isospin dependence
- Residual interactions change
or (dis)appear
Shell quenching or new closures
Astrophysical
importance!!!
Probing the shell structure near 68,78Ni
“Island of inversion”
Experimental set-up
MINIBALL
Gammaspectroscopy
Particles
• angles
• energies
Beam
monitor
Beam
impurities
MINIBALL
DSSSD
Beams from
REX-ISOLDE
@ 2.85 MeV/u
• “Safe” Coulomb excitation or transfer reactions
• Gamma – particle coincidences
• Isobaric beam contaminants
PPAC
Beam Dump
Detector
DE Si detector
IC - Si
telescope
or
Bragg detector
B(E2) systematics around 132Sn
138,140,142,144Xe
Low B(E2) values
in Sn and Te isotopes
D. Radford et al.,
PRL 88, 222501 (2002)
BUT:
(a) Recent experiment:
30% larger B(E2) values!!!
C. Baktash, MAFF ’05
(b) larger B(E2) value deduced
from t of 2+ state in 136Te
L. M. Fraile (F2-2)
122,124,126Cd
• Coulex of 122,124,126Cd and 138,140,142,144Xe
• Cd and Xe beams unique to ISOLDE
• heaviest beams delivered to MINIBALL so far ...
Proposed
theoretical explanation:
Reduced neutron paring
above N=82
low B(E2) and E(2+)
J. Terasaki et al.,
PRC 66, 054313 (2002)
B(E2) values of Cd and Xe isotopes
systematics:
modified Grodzins‘ rule
D. Habs, R. Krücken
p SM
q BMF
 REX-ISOLDE
--- systematics
 REX-ISOLDE
--- systematics
SM: A. Scherillo et al.,
PRC 70, 054318 (2004)
BMF: A. Jungclaus et al.,
NUSTAR (2007)
p QRPA
q MCSM
QRPA: J. Terasaki et al.,
PRC 66, 054313 (2002)
MCSM: N. Shimizu et al.,
J. Phys.: Conf. Ser. 49,
178 (2006)
• preliminary B(E2) values agree with systematics
• agreement with theory (... not yet decisive)
• B(E2) anomaly in 136Te seems to be a well localised effect
Planned for the future:
• Coulex of 128Cd (N=82 quenching??) and 140,148,150Ba
• g-factor of 2+ state in 136Te and 138Xe
Analysis by
T. Behrens, Th. Kröll,
R. Krücken
TU München
Shell evolution from N=40 to N=50 (I)
68Ni 78Ni
Zn Ge
N=40
N=50
Coulex of neutron-rich
74,76,78,80Zn
E(2+1) [keV]
• first observation of excited 2+ state in 80Zn
• good agreement with large scale shell
model calculations:
--- N. Smirnova et al., (2006)
··· A. F. Lisetskiy et al., (2006)
B(E2, 2+10+1) [W.u.]
ng9/2

• N=50 remains strong shell closure
• no particular effect at N=40
• for N>40 E(2+)-values overestimated
• large effective charges needed
weakening of Z=28 (56Ni core polarisation)
Zn
80Zn
Analysis by
J. Van de Walle, P. Van Duppen
KU Leuven
J. Van de Walle et al.,
submitted to PRL
Neutron Number
Shell evolution from N=40 to N=50 (II)
6- (isomer)
1+ (gs)
Resonant Laser Ionisation Ion Source (RILIS)
Coulex of 68Cu,68mCu,70Cu
Post-acceleration of
selectively ionised isomeric beam!

• poor agreement with SM for 68,72Cu
(56Ni core, N. Smirnova, 2006) indicates
proton excitations across the Z=28 shell gap
• 70Cu shows stabilising effect of 68Ni (N=40)
• Coulex of odd-even
(under analysis)
67,69,71,73Cu
Analysis by
I. Stefanescu, P. Van Duppen (KU Leuven)
G. Georgiev (CERN / CSNSM Orsay)
I. Stefanescu et al., PRL 98, 122701 (2007)
Collectivity of the Mg isotopes
Coulex of 30,32Mg
“Island of Inversion”
- disappearance of N=20 shell closure for neutron-rich nuclei
30Mg
MSU
MSU
241  31 e2fm4
PRL 94, 172501 (2005)
434  52 e2fm4
to be published
is OUTSIDE
and
32Mg is INSIDE
of the
“Island of Inversion”
• Good agreement with
large-scale SM
calculations breaking
N=20 for 32Mg
Analysis by
O. Niedermaier, H. Scheit,
V. Bildstein, D. Schwalm
MPI-K Heidelberg
Next step … transfer reactions
normal
sd
configurations
Shore of the „island of inversion“
New Si detector array
... fits inside MINIBALL
MINIBALL
31Al
32Al
33Al
34Al
30Mg
31Mg
32Mg
33Mg
29Na
30Na
31Na
34Mg
intruder
fp
configurations
First experiments planned: 2,3H (30Mg, 31,32Mg) 1H
 Study of single-particle configurations
of excited states
beam
V. Bildstein, Th. Kröll et al.
Collaboration:
TUM, KU Leuven, ...
Summary
• “Safe” Coulomb excitation of
neutron-rich isotopes
generally good agreement with
large scale shell model
calculations
modifications of shell structure
• Transfer reactions are on the way
single-particle properties
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• Upgrade of REX to HIE-ISOLDE
(L. M. Fraile, J2-3)
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