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Spectroscopy of neutron-rich nuclei at REX-ISOLDE with MINIBALL

Spectroscopy of neutron-rich nuclei at REX-ISOLDE with MINIBALL. Thorsten Kr öll Physik-Department E12, TU München, Germany Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik, Garching, Germany. Outline. Milestone of nuclear structure Shell model è magic numbers

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Spectroscopy of neutron-rich nuclei at REX-ISOLDE with MINIBALL

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  1. Spectroscopy of neutron-rich nucleiat REX-ISOLDE with MINIBALL Thorsten Kröll Physik-Department E12, TU München, Germany Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik, Garching, Germany

  2. Outline Milestone of nuclear structure Shell model è magic numbers Do they persist far-off stability? è Study of radioactive nuclei!!! B(E2) values around 132Sn • Mean field + residual interactions • - Isospin dependence • - Residual interactions change • or (dis)appear • Shell quenching or new closures r-process Astrophysical importance!!! Probing the shell structure near 68,78Ni “Island of inversion”

  3. Experimental set-up Beam monitor Beam impurities Gamma- spectroscopy • Particles • angles • energies MINIBALL MINIBALL Beam Dump Detector PPAC DSSSD Beams from REX-ISOLDE @ »2.85 MeV/u DE Si detector IC - Si telescope or Bragg detector • “Safe” Coulomb excitation or transfer reactions • Gamma – particle coincidences • Isobaric beam contaminants

  4. 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 ... B(E2) systematics around 132Sn 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) valuededuced from t of 2+ state in 136Te L. M. Fraile (F2-2) Proposed theoretical explanation: Reduced neutron paring above N=82 Þ low B(E2) and E(2+) J. Terasaki et al., PRC 66, 054313 (2002)

  5. B(E2) values of Cd and Xe isotopes systematics: modified Grodzins‘ rule D. 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) p SM q BMF • REX-ISOLDE --- systematics p QRPA q MCSM • REX-ISOLDE --- systematics • 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

  6. Shell evolution from N=40 to N=50 (I) • 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) • Þ • N=50 remains strong shell closure • no particular effect at N=40 • for N>40 E(2+)-values overestimated • large effective chargesneeded • Û weakening of Z=28 (56Ni core polarisation) N=50 78Ni 68Ni Zn N=40 Ge E(2+1) [keV] ng9/2 B(E2, 2+10+1) [W.u.] Zn Analysis by J. Van de Walle, P. Van Duppen KU Leuven J. Van de Walle et al., submitted to PRL 80Zn Neutron Number

  7. Shell evolution from N=40 to N=50 (II) 6-(isomer) Resonant Laser Ionisation Ion Source (RILIS) 1+(gs) • Coulex of 68Cu,68mCu,70Cu • Post-acceleration of • selectively ionised isomeric beam! • Þ • 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) Analysis by I. Stefanescu, P. Van Duppen (KU Leuven) G. Georgiev (CERN / CSNSM Orsay) I. Stefanescu et al., PRL 98, 122701 (2007)

  8. Collectivity of the Mg isotopes Coulex of 30,32Mg “Island of Inversion” - disappearance of N=20 shell closure for neutron-rich nuclei • 30Mg is OUTSIDE • and • 32Mg is INSIDE • of the • “Island of Inversion” • Good agreement with • large-scale SM • calculations breaking • N=20 for 32Mg MSU MSU 241 ± 31 e2fm4 PRL 94, 172501 (2005) 434 ± 52 e2fm4 to be published Analysis by O. Niedermaier, H. Scheit, V. Bildstein, D. Schwalm MPI-K Heidelberg

  9. Next step … transfer reactions Shore of the „island of inversion“ New Si detector array ... fits inside MINIBALL normal sd configurations MINIBALL 31Al 33Al 34Al 32Al 30Mg 33Mg 34Mg 32Mg 31Mg intruder fp configurations 31Na 29Na 30Na beam • First experiments planned: 2,3H (30Mg, 31,32Mg) 1H • Study ofsingle-particle configurations of excited states V. Bildstein, Th. Kröll et al. Collaboration: TUM, KU Leuven, ...

  10. 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 • Upgrade of REX to HIE-ISOLDE • (L. M. Fraile, J2-3) l l l l l l l l l l l l l l l l l l l l l l l l l l l l Thank you for your attention!!! l l l l

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