Spectroscopy of neutronrich nuclei at REXISOLDE with MINIBALL

Spectroscopy of neutron-rich nuclei at REX-ISOLDE with MINIBALL Thorsten Kröll Physik-Department E 12, TU München, Germany Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik, Garching, Germany

Outline Milestone of nuclear structure Shell model èmagic numbers B(E 2) values around 132 Sn Do they persist far-off stability? èStudy of radioactive nuclei!!! • Mean field + residual interactions - Isospin dependence - Residual interactions change or (dis)appear èShell quenching or new closures r-p s s e oc r Astrophysical importance!!! Probing the shell structure near 68, 78 Ni “Island of inversion”

Experimental set-up MINIBALL Gammaspectroscopy Particles • angles • energies Beam monitor Beam impurities MINIBALL DSSSD Beams from REX-ISOLDE @ » 2. 85 Me. V/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(E 2) systematics around 132 Sn 138, 140, 142, 144 Xe Low B(E 2) values in Sn and Te isotopes D. Radford et al. , PRL 88, 222501 (2002) BUT: (a) Recent experiment: 30% larger B(E 2) values!!! C. Baktash, MAFF ’ 05 (b) larger B(E 2) value deduced from t of 2+ state in 136 Te L. M. Fraile (F 2 -2) 122, 124, 126 Cd • Coulex of 122, 124, 126 Cd and 138, 140, 142, 144 Xe • Cd and Xe beams unique to ISOLDE • heaviest beams delivered to MINIBALL so far. . . Proposed theoretical explanation: Reduced neutron paring above N=82 Þ low B(E 2) and E(2+) J. Terasaki et al. , PRC 66, 054313 (2002)

B(E 2) values of Cd and Xe isotopes systematics: modified Grodzins‘ rule D. Habs, R. Krücken p SM q BMF ¢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(E 2) values agree with systematics • agreement with theory (. . . not yet decisive) • B(E 2) anomaly in 136 Te seems to be a well localised effect Planned for the future: • Coulex of 128 Cd (N=82 quenching? ? ) and 140, 148, 150 Ba • g-factor of 2+ state in 136 Te and 138 Xe Analysis by T. Behrens, Th. Kröll, R. Krücken TU München

Shell evolution from N=40 to N=50 (I) 68 Ni 78 Ni Zn Ge N=40 N=50 74, 76, 78, 80 Zn E(2+1) [ke. V] • first observation of excited 2+ state in 80 Zn • good agreement with large scale shell model calculations: --- N. Smirnova et al. , (2006) ··· A. F. Lisetskiy et al. , (2006) ng 9/2 B(E 2, 2+1 0+1) [W. u. ] Coulex of neutron-rich Þ • N=50 remains strong shell closure • no particular effect at N=40 • for N>40 E(2+)-values overestimated • large effective charges needed Û weakening of Z=28 (56 Ni core polarisation) Zn 80 Zn 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 68 Cu, 68 m. Cu, 70 Cu Post-acceleration of selectively ionised isomeric beam! Þ • poor agreement with SM for 68, 72 Cu (56 Ni core, N. Smirnova, 2006) indicates proton excitations across the Z=28 shell gap • 70 Cu shows stabilising effect of 68 Ni (N=40) • Coulex of odd-even 67, 69, 71, 73 Cu (under analysis) 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, 32 Mg “Island of Inversion” - disappearance of N=20 shell closure for neutron-rich nuclei 30 Mg MSU 241 ± 31 e 2 fm 4 PRL 94, 172501 (2005) 434 ± 52 e 2 fm 4 to be published is OUTSIDE and 32 Mg is INSIDE of the “Island of Inversion” • Good agreement with large-scale SM calculations breaking N=20 for 32 Mg 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 31 Al 32 Al 33 Al 34 Al 30 Mg 31 Mg 32 Mg 33 Mg 29 Na 30 Na 31 Na 34 Mg intruder fp configurations First experiments planned: 2, 3 H (30 Mg, 31, 32 Mg) 1 H Þ 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 Þ generally good agreement with large scale shell model calculations Þ modifications of shell structure • Transfer reactions are on the way Þ single-particle properties l l l • Upgrade of REX to HIE-ISOLDE (L. M. Fraile, J 2 -3) ou y k n a Th !!! n o i t n te t a r u for yo l ll ll l l l l