Intermediate-energy Coulomb excitation of ^{58,60,62}Cr: The onset of collectivity toward N=40

Intermediate-energy Coulomb excitation measurements were performed on the neutron-rich isotopes 58,60,62Cr. The electric quadrupole excitation strengths, B(E2; 01+→21+), of 60,62Cr are determined for the first time. The results quantify the trend of increasing quadrupole collectivity in the Cr isotopes approaching neutron number N=40. The results are confronted with large-scale shell-model calculations in the fpgd shell using the state-of-the-art LNPS effective interaction. Different sets of effective charges are discussed that provide an improved and robust description of the B(E2) values of the neutron-rich Fe and Cr isotopes in this region of rapid shell evolution. The ratio of the neutron and proton transition matrix elements, |Mn/Mp|, is proposed as an effective tool to discriminate between the various choices of effective charges.