Deformed state admixtures in mass-42 nuclei

Abstract

We have attempted to explain the energy spectrum and transition rates in 42Ca and 42Sc by considering admixtures of 4p-2h deformed and 2p spherical shell-model states for the low-lying levels. Two methods of handling the 4p-2h deformed states have been considered; both treat the four-particle wave function in the same way but in the first method the two holes occupy a deformed orbit in a similar way to the four particles, while in the more extended second method the four-particle states are coupled to a complete set of two-hole states in the s-d shell. Using three variational parameters (the deformation parameters) and three fitted parameters (effective charge, f 7 2 − d 3 2 energy splitting and the overlap between spherical and deformed 40Ca cores), we have reproduced to a good approximation (in the case of the extended model) the positive-parity spectrum and the transition rates of 42Ca up to 3.4 MeV excitation energy. With this model we have also accounted for the two 1 + states recently observed at about 2 MeV excitation in the T = 0 spectrum of 42Sc, and have explained the large number of low-lying levels in the spectrum of this nucleus. The simpler model has been used to investigate the nature of some pure deformed states in the low-lying spectrum of 42Sc which have probably not yet been detected experimentally.