Revealing New Structures in Odd–odd ^54 Mn Nucleus

The excited states of odd–odd ^54 Mn ( Z=25, N=29 ) nucleus have been investigated using the fusion evaporation reaction ^55 Mn( α , α 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 γ -ray transitions. Spin and parity (J ^π ) of most of the levels in the revised level scheme have been firmly assigned. The placement of some of the already known γ rays in the level scheme and J ^π assignments of some of the levels reported earlier have also been revised. The new level scheme, which has been extended up to ∼ 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. E 3 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.