Relativistic Coulomb excitation of neutron-rich Cr-54,Cr-56,Cr-58 : On the pathway of magicity from N=40 to N=32

The first excited 2(+) states in Cr-54,Cr-56,Cr-58 were populated by Coulomb excitation at relativistic energies and gamma rays were measured using the RISING setup at GSI. For Cr-56 and Cr-58 the B(E2, 2(1)(+) -> 0(+)) values relative to the previously known B(E2) value for Cr-54 are determined as 8.7(3.0) and 14.8(4.2) W.u., respectively. The results are consistent with a subshell closure at neutron number N = 32 which was already indicated by the higher energy of the 2+ state in 56Cr. Recent large-scale shell model calculations using effective interactions reproduce the trend in the excitation energies, but fail to account for the minimum in the B(E2) values at N = 32. (c) 2005 Elsevier B.V. All rights reserved.