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

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