Intermediate-energy Coulomb excitation of 58 ,60 ,62Cr: 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; 0+ 1 → 2+ 1 ), 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
This work was funded by the National Science Foundation under Contract No. PHY-0606007; by the US Department of Energy, Office of Nuclear Physics, under Contracts No. DE-AC02-06CH11357 and No. DE-FG02-08ER41556, and by the United Kingdom Science and Technology Facilities Council (STFC). A.P. is supported by the MICINN (Spain) (Grant No. FPA2011-29854) and by the Comunidad de Madrid (Spain) (Grant No. HEPHACOS S2009-ESP-1473)