The low-energy level structures of ${}_{25}^{64}$Mn${}_{39}$ and ${}_{25}^{66}$Mn${}_{41}$ were investigated through both the decay of Mn metastable states and the population of levels following the $\beta$ decay of ${}^{64}$Cr and ${}^{66}$Cr. The deduced level schemes and tentatively assigned spins and parities suggest the coexistence of spherical and deformed configurations above and below $N=40$ for the odd-odd Mn isotopes. The low-energy deformed configurations are attributed to the coupling between a proton in a $K=1/2^{-}$ level with neutrons in either the $K=1/2^{-}$ or the $K=3/2^{+}$ levels originating from the $\pi p_{3/2}$, $\nu p_{1/2}$, and $\nu g_{9/2}$ single-particle states, respectively.

• Received 13 October 2011

DOI:https://doi.org/10.1103/PhysRevC.84.061305