Evolution of collective behaviour among thorium nuclides spanned between the drip lines

Abstract

The study of atomic nuclei is important in the context of in a wide variety of applications, In particular, nuclear energy, nuclear medicine, and trace element analysis etc. also, it is relevant in the context of astrophysical applications, the stellar evolution, nucleosynthesis and in nuclear reactions. In order to analyse the complete behaviour of a nucleus, based on experimental results, different theoretical models are necessary. Nowadays several theoretical approaches are available in the literature, to explain the static properties and collective behaviour of atomic nuclei. Single particle excitation and collective excitation are the possible excitation modes in a nucleus. The main objectives of this thesis work is to investigate the structure properties of thorium nuclei lying on and off the valley of β-stability. The studies can be broadly classified into two, aiming to understand the ground state properties and the dynamic properties of thorium isotopes. For the structure study, the nuclear level density is one of the important factors. The level density of thorium nuclei were estimated by different phenomenological models of level density. The nuclear structure properties like binding energy, charge radii, rms radii and its isotopic shift, two-neutron separation energy and shell gap, chemical potential, quadrupole deformation, density distribution and single- particle energy of thorium nuclei, lying on and off the line of β-stability are estimated. This study will help us understand the variation of nuclear properties with neutron number and to predict the shell closure and nuclear stability. Broken linearities were observed at around neutron numbers N=126, 138 and 184 in the plots of various evaluated values against neutron number. Single-particle energy gaps were evaluated at around these neutron numbers. Large deviation and shell gaps were observed at around the neutron numbers N=126 and 184. Hence, these numbers are neutron magic numbers and the corresponding thorium nuclei are more stable than their neighbours. A small deviation and shell gap were observed at around N=138, and hence we conclude that this neutron number is semi-magic and the associated nucleus is relatively stable. Most of the thorium nuclei are of prolate shape. However, they are spherical at N=126 and 184.