Spectroscopy of Mn-65,67(25): Strong coupling in the N=40 island of inversion

Excited states in Mn-63,Mn-65,Mn-67 were studied via in-beam gamma-ray spectroscopy following knockout reactions from Fe-68. Similar level schemes, consisting of the 11/2(-), 9/2(-), 7/2(-) and 5/2(g.s.)(-) level sequence, connected by I -> I - 1 transitions, were established, the first time for Mn-65,Mn-67. Their level structures show features consistent with strongly-coupled rotational bands with K= 5/2. State-of-the-art shellmodel calculations with the modified LNPS effective interaction reproduce the observed levels remarkably well and suggest the dominance of 4-particle-4-hole neutron configurations for all the states. The data on the low-lying excited states of odd-mass Mn53-67 provide a textbook example of nuclear structure evolution from weak coupling through decoupling to strong coupling along a single isotopic chain on the n-rich side of the beta stability line. These results help to deepen our understanding of the N= 40 island of inversion. (c) 2018 The Authors. Published by Elsevier B.V.