The structure of neutron-rich Cr isotopes is systematically investigated by using the spherical shell model. The calculations reproduce well the known energy levels for the even-even ${}^{52-62}\mathrm{Cr}$ and odd-mass ${}^{53-59}\mathrm{Cr}$ nuclei, and predict a lowering of excitation energies around neutron number $N=40$. The calculated $B(E2;2_1^{+}\to 0_1^{+})$ systematics shows a pronounced collectivity around $N=40$; a similar characteristic behavior has been suggested for Zn and Ge isotopes. Causes for the sudden drop of the $9/2_1^{+}$ energy in ${}^{59}\mathrm{Cr}$ and the appearance of very low $0_2^{+}$ states around $N=40$ are discussed. We also predict a new band with strong collectivity built on the $0_2^{+}$ state in the $N=40$ isotope ${}^{64}\mathrm{Cr}$.

• Received 8 July 2008

DOI:https://doi.org/10.1103/PhysRevC.78.064312