Microscopic study of positive-parity yrast bands of 224a?’234Th isotopes

摘要

The positive-parity bands in 224a?’234Th are studied using the projected shell model (PSM) approach. The energy levels, deformation systematics, e??μ(e???2) transition probabilities and nuclear e?‘”-factors are calculated and compared with the experimental data. The calculation reproduces the observed positive-parity yrast bands and e??μ(e???2) transition probabilities. Measurement of e??μ(e???2) transition probabilities for higher spins and e?‘”-factors would be a stringent test for our predictions. The results of theoretical calculations indicate that the deformation systematics in 224a?’234Th isotopes depend on the occupation of low e?‘? components of high j orbits in the valence space and the deformation producing tendency of the neutrona€“proton interaction operating between spin orbit partner (SOP) orbits, the $[(2g_{9/2}_{e???}) - (2g_{7/2})_{e???}]$ and $[(1i_{13/2})_{e???} - (1i_{11/2})_{e???}]$ SOP orbits in the present context. In addition, the deformation systematics also depend on the polarization of $(1h_{11/2})_{e???}$ orbit. The low-lying states of yrast spectra are found to arise from 0-quasiparticle (qp) intrinsic states whereas the high-spin states turn out to possess composite structure.