SHELL MODEL STUDY OF BETA DECAYS AND ELECTRON CAPTURE RATES

Abstract

In the present thesis work, we aim to study the nuclear structure and beta-decay properties of nuclei in the heavier mass region using large-scale shell-model calculations. Additionally, we have also explored the stellar weak interaction rates of the URCA pairs nuclei. We report a comprehensive shell-model study of the log ft values for the forbidden β− decay transitions in the region northeast of 208Pb. For this, we have considered 210−215Pb → 210−215Bi and 210−215Bi → 210−215Po transitions. We have performed shell-model calculation using the KHPE interaction in valence shells 82 − 126 for protons and 126−184 for neutrons without any truncation. We have also calculated half-lives and Q values for the concerned nuclei. Recently, several log ft values were observed corresponding to β− decay from the (8−) isomeric state of 2145Bim at the CERN-ISOLDE facility by Andel et al., and for the first time we have reported shell-model results for these transitions. We have performed the large-scale shell-model calculations for the β− decay properties of the neutron-rich nuclei in the south region of 208Pb in the nuclear chart with 76 ≤ Z ≤ 82. These beta-decay properties include log ft, average shape factor values, half-lives, and partial decay rates calculated for these neutron-rich nuclei using recent effective interaction for the 208Pb region. These calculations have been performed without truncation in a particular model space for nuclei N ≤ 126; additionally, particle-hole excitations are included in the case of core-breaking nuclei (Z ≤ 82,N > 126). An extensive comparison with the experimental data has been made, and spin parities of several states have been proposed.