High-Kband of unnatural parity in49Cr

Abstract

The nucleus ${}^{49}\mathrm{Cr}$ has been studied using the reactions ${}^{28}\mathrm{Si}{(}^{28}\mathrm{Si},\ensuremath{\alpha}2pn)$ at 115 MeV and ${}^{46}\mathrm{Ti}(\ensuremath{\alpha},n)$ at 12 MeV, respectively. A high-$K$ band with ${K}^{\ensuremath{\pi}}{=13/2}^{+}$ has been identified, whose bandhead acts as an yrast trap for the low-lying levels with positive parity. This peculiar phenomenon is well reproduced by large-scale shell model calculations in the $\mathrm{pf}$ configuration space plus a proton hole in the ${1d}_{3/2}$ orbital. As an essential part of the work, lifetimes of some nonyrast states, as well as of a state in the ${K}^{\ensuremath{\pi}}{=5}^{+}$ band in ${}^{50}\mathrm{Mn},$ have been determined using the Doppler shift attenuation method.