Collectivity in neutron-rich Mn isotopes

The rapid development of collectivity in the N = 40 region as protons are removed from the f$_{7/2}$ single-particle state is suggested by the dramatic drop in energy of the first excited $2^{+}$ state from $^{68}$Ni to $^{66}$Fe and the increase in B (E2) along the Fe isotopic chain. Recent large-scale shell model calculations which include the g$_{9/2}$ and d$_{5/2}$ single-particle states have attributed the increased collectivity in the Cr and Fe nuclei to the influence of multi- particle neutron excitations across N = 40. While a variety of experiments have focused on even-even nuclei, including Cr and Fe, very little is known about the odd-Z isotopes. To explore the influence of the intruder neutron g$_{9/2}$ and d$_{5/2}$ states, the beta decays of the Cr isotopes into the respective Mn nuclei were studied at the NSCL. Preliminary low-energy level structures for the Mn isotopes will be presented.