NUCLEAR STRUCTURE STUDY FROM MICROSCOPIC EFFECTIVE INTERACTIONS

Abstract

The structural properties of exotic nuclei far from the stability line change remarkably compared to their stable counterparts. A fundamental goal of nuclear structure physics is to explain these structural phenomena and their evolution from first principles or underlying nucleon-nucleon forces. The present thesis studies the structural characteristics of stable and exotic isotopes across different mass regions of the nuclear chart within the shell model framework from microscopic effective interactions, which were derived from realistic two- and three-nucleon potentials using modern ab initio approaches. The isoscalar, isovector, and orbital contributions to M1 transitions have been investigated in the T=1/2 mirror nuclei within sd-shell using phenomenological and ab initio coupled cluster effective interactions. In particular, contributions of the orbital term associated with the M1 transitions and ground-state magnetic moments are extracted from analogous M1 and Gamow-Teller (GT) transitions between mirror pairs. It is demonstrated that the orbital contributions are strongly influenced by the configurations of the initial and final states involved, and the deformed nuclei tend to exhibit relatively larger orbital contributions. The structural properties of Na isotopes, including ground-state energies, low-lying spectra, E2 transition, ground-state moments, and radii, have been studied from various microscopic effective interactions. These interactions are derived from different realistic two- or/and three-nucleon potentials for the sd-shell within ab initio No Core Shell Model (NCSM) and In-medium Similarity Renormalization Group (IMSRG) frameworks. The study provides a detailed one-to-one comparison of the low-energy properties of Na isotopes predicted by different effective interactions. We have investigated the breaking of the N = 20 shell gap and the emergence of new magic numbers at N = 32 and 34 in exotic isotopes using valence space effective interactions derived from chiral 2N and 3N forces employing the IMSRG method. The N = 20 shell gap breaking is studied from the evolution of singleparticle states in odd-A Ne and Mg isotopes, and their transition into the island of inversion region is discussed through particle-hole excitations across the shell gap. Our study establishes rotational band structures arising from normal and intruder configurations at low excitation energies and predicts shape coexistence in 31,33Mg. The magicity at N = 32 and 34 is investigated in the neutron-rich region around Ca with 14  Z  26. The calculated results fairly reproduced the available experimental data and suggested a strengthened N = 34 shell gap below Ca while the N = 32 shell gap weakens or disappears. Through spin-tensor decomposition, we analyzed the contributions of various components of nuclear force, such as central, spin-orbit, and tensor, and discussed their roles in establishing shell gaps far from the stability line. Our findings indicate a deformed ground state band in N = 32 isotones with Z < 20.