Spectroscopy of neutron-rich nucleiat REX-ISOLDE with MINIBALL

Thorsten KröllPhysik-Department E12, TU München, Germany

Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik, Garching, Germany

OutlineOutline

Probing the shell structure near 68,78Ni

B(E2) values around 132Sn

“Island of inversion”

Milestone of nuclear structureShell model magic numbers

Do they persist far-off stability? Study of radioactive nuclei!!!

• Mean field + residual interactions - Isospin dependence - Residual interactions change or (dis)appearShell quenching or new closures

r-process

Astrophysicalimportance!!!

Experimental set-upExperimental set-up

DSSSD PPAC

MINIBALL

Beam DumpDetector

Gamma-spectroscopy

Particles• angles• energies

Beammonitor

Beamimpurities

IC - Sitelescope

orBragg detector

E Si detector

• “Safe” Coulomb excitation or transfer reactions• Gamma – particle coincidences• Isobaric beam contaminants

MINIBALL

Beams fromREX-ISOLDE

@ 2.85 MeV/u

B(E2) systematics around B(E2) systematics around 132132SnSn

Low B(E2) valuesin 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) valuededuced from of 2+ state in 136Te L. M. Fraile (F2-2)

Proposedtheoretical explanation:Reduced neutron paring

above N=82low B(E2) and E(2+)

J. Terasaki et al., PRC 66, 054313 (2002)

138,140,142,144Xe

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 ...

Analysis byT. Behrens, Th. Kröll,

R. KrückenTU München

systematics: modified Grodzins‘ ruleD. Habs, R. Krücken

SM: A. Scherillo et al., PRC 70, 054318 (2004)BMF: A. Jungclaus et al., NUSTAR (2007)

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

QRPA MCSM

SM BMF

B(E2) values of Cd and Xe isotopesB(E2) values of Cd and Xe isotopes

REX-ISOLDE--- systematics

REX-ISOLDE--- systematics

Zn Ge68Ni 78Ni

Analysis byJ. Van de Walle, P. Van Duppen

KU Leuven

J. Van de Walle et al.,submitted to PRL

Shell evolution from N=40 to N=50 (I)Shell evolution from N=40 to N=50 (I)

Neutron Number

Zn

B(E

2, 2

+1

0+1)

[W

.u.]

E(2

+1)

[ke

V]

80Zn

N=40 N=50 Coulex of neutron-rich 74,76,78,80Zn

• 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) • N=50 remains strong shell closure• no particular effect at N=40• for N>40 E(2+)-values overestimated• large effective chargesneeded weakening of Z=28 (56Ni core polarisation)

g9/2

Shell evolution from N=40 to N=50 (II)Shell evolution from N=40 to N=50 (II)

Analysis byI. Stefanescu, P. Van Duppen (KU Leuven)

G. Georgiev (CERN / CSNSM Orsay)

I. Stefanescu et al., PRL 98, 122701 (2007)

6- (isomer)

1+ (gs)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 67,69,71,73Cu (under analysis)

Resonant Laser Ionisation Ion Source (RILIS)

Collectivity of the Mg isotopesCollectivity of the Mg isotopes

30Mg is OUTSIDEand

32Mg is INSIDEof the

“Island of Inversion”

• Good agreement with large-scale SM calculations breaking N=20 for 32Mg241 31 e2fm4

PRL 94, 172501 (2005)

MSU

MSU

434 52 e2fm4

to be publishedAnalysis by

O. Niedermaier, H. Scheit,V. Bildstein, D. Schwalm

MPI-K Heidelberg

Coulex of 30,32Mg“Island of Inversion” - disappearance of N=20 shell closure for neutron-rich nuclei

Next step … transfer reactions Next step … transfer reactions

MINIBALL

beam

V. Bildstein, Th. Kröll et al.Collaboration:

TUM, KU Leuven, ...

30Mg

29Na

33Al32Al31Al

normalsd

configurations

intruderfp

configurations

31Mg 32Mg

30Na 31Na

34Al

33Mg

Shore of the „island of inversion“

34Mg

New Si detector array ... fits inside MINIBALL

First experiments planned: 2,3H (30Mg, 31,32Mg) 1H Study ofsingle-particle configurations of excited states

SummarySummary

Thank you

for your attention!!!

• “Safe” Coulomb excitation of neutron-rich isotopes generally good agreement with large scale shell model calculationsmodifications of shell structure

• Transfer reactions are on the way single-particle properties

• Upgrade of REX to HIE-ISOLDE (L. M. Fraile, J2-3)