In-Beam Gamma-Ray Spectroscopy Of Cr-62,Cr-64

The region of neutron-rich Cr isotopes has garnered much attention in recent years due to a rapid onset of collectivity near neutron number N = 40. We report here on the first gamma-ray spectroscopy beyond the (4i) state in Cr-62,(64), using nucleon removal reactions from several projectiles within a rare-isotope beam cocktail. A candidate for the 6+ state in 64 Cr is presented as well as one for, possibly, the second excited 0(+) state in Cr-62. The results are discussed in comparison to the LNPS shell-model predictions that allow for neutron excitations across the N = 40 harmonic oscillator gap into the g(9)(/2 )and d(5/2) orbitals. The calculated level schemes for Cr-62,Cr-64 reveal intriguing collective structures. From the predicted neutron particle-hole character of the low-lying states in these Cr isotopes, Cr-62 emerges as a transitional system on the path to the center of the N = 40 island of inversion.