Five-dimensional quasispin and the spectra of odd-parity yrast configurations in the Ba region

Abstract

The 5-dimensional quasispin formalism is used to evaluate the (n, T)-dependent factors of the matrix elements of abnormal parity operators of relevance for yrast-band spectroscopy. The formalism allows the leading pseudo-SU(3) representation of the normal (N) parity part of a shell-model configuration to be coupled to low-seniority states of the abnormal (A) parity high-j intruder part of the configuration. To illustrate the importance of the nA, TA dependence of the (A) to (N) space-coupling matrix elements this model is applied to the negative-parity yrast spectra of 127La and 127Ba, using hamiltonian parameters which give a reasonable fit for 126Ba. The 127La spectrum is reproduced with a seniority-one truncation of the h11/2 configuration; the 127Ba spectrum indicates a need for higher-seniority admixtures.