Revealing new structures in odd–odd $^{54}$Mn nucleus

Abstract

The excited states of odd–odd $^{54}$Mn ($Z=25, N=29$) nucleus have been investigated using the fusion evaporation reaction $^{55}$Mn($\alpha$, $\alpha$n)$^{54}$Mn at the beam energy of 34 MeV. A new and improved level scheme of $^{54}$Mn has been proposed in this work with the placement of 22 new $\gamma$-ray transitions. Spin and parity (J$^\pi$) of most of the levels in the revised level scheme have been firmly assigned. The placement of some of the already known $\gamma$ rays in the level scheme and J$^\pi$ assignments of some of the levels reported earlier have also been revised. The new level scheme, which has been extended up to $\sim$6 MeV, provides new insight and interesting structural aspects of the generation of high angular momentum in this odd–odd Mn isotope with neutron number ($N=29$) just above the $N=28$ shell gap. Three octupole-phonon-coupled negative parity states have been identified for the first time in this nucleus. E3 transitions have also been observed to decay from these states. Shell model calculations with two different interactions i.e. kb3gpn and gx1pn have been performed which well reproduced the low-lying, few-particle states but fail to reproduce the higher-lying multi-particle states. These higher-lying states have been understood as resulting from collective excitations. An oblate minimum obtained from the Total Routhian Surface calculations provides support to this conjecture.