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Collectivity of the 4+ state in 70ZN studied via Coulomb excitation

Abstract : Shell evolution in the vicinity of 68Ni has recently attracted many theoretical and experimental investigations. By now it has been clearly established that the presumed subshell closure at N=40 is not very pronounced. While the intruder character of the 1g9/2 and 2d5/2 neutron orbital induces collectivity by pair excitations from the fp shell into the g9/2 orbital, the parity change hinders quadrupole excitations and therefore mimics the properties of a doubly magic nucleus in 68Ni, i.e., a high 21+ energy and a low B(E2; 2+ → 0+) value. Adding valence nucleons to the N=40 open shell leads to a rapid increase of collectivity, with an interplay of both collective and single-particle degrees of freedom. Such rapid changes indicate underlying complex effects and make this region ideal for testing theoretical calculations. While measurements of B(E2; 2+ → 0+ ) values are useful to investigate the evolution of collectivity along isotopic chains, even more insight into the collective behavior can be gained by measuring lifetimes of higher-lying states. Almost all stable and neutron-rich Zn isotopes present an anomalously low B(E2; 4+ → 2+)/ B(E2; 2+ → 0+) ratio of 1 or less, which is normally observed only around closed shells. A strong increase of collectivity of the 4+ state was observed for 70Zn [2] and could not be explained in the framework of nuclear structure models. A recent lifetime measurement [2] yielded a considerably longer lifetime of this state, yet its accuracy was not sufficient to draw firm conclusions. Given the complex scheme of low-lying states in 70Zn including many nearly degenerate transitions, Coulomb excitation seemed a more appropriate method to study this nucleus. A dedicated Coulomb excitation measurement has been recently performed at the Heavy Ion Laboratory, University of Warsaw, to measure B(E2; 4+ → 2+) in 70Zn. For this study, the EAGLE array coupled to a compact setup of 48 PIN-diodes was used. The preliminary result will be presented.
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http://hal.in2p3.fr/in2p3-00837700
Contributor : Michel Lion <>
Submitted on : Monday, June 24, 2013 - 10:46:54 AM
Last modification on : Monday, February 10, 2020 - 6:13:05 PM

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M. Zielinska, E. Clément, A. Drouart, K. Hadynska-Klek, J. Iwanicki, et al.. Collectivity of the 4+ state in 70ZN studied via Coulomb excitation. Nuclear Structure Physics with Advanced Gamma-Detector Arrays (NSP13), Jun 2013, Padova, Italy. ⟨in2p3-00837700⟩

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