Single-Particle and Collective Structures in Neutron-Rich Sr Isotopes

Kamila Sieja

doi:10.3390/universe8010023

Abstract

Neutron-rich Sr nuclei around N=60 exhibit a sudden shape transition from a spherical ground state to strongly prolate-deformed. Recently, much new insight into the structure of Sr isotopes in this region has been gained through experimental studies of the excited levels, transition strengths, and spectroscopic factors. In this work, a “classic” shell model description of strontium isotopes from N=50 to N=58 is provided, using a natural valence space outside the 78Ni core. Both even–even and even–odd isotopes are addressed. In particular, spectroscopic factors are computed to shed more light on the structure of low-energy excitations and their evolution along the Sr chain. The origin of deformation at N=60 is mentioned in the context of the present and previous shell model and Monte Carlo shell model calculations.

Highlights

Strontium (Z = 38) and zirconium (Z = 40) isotopes exhibit a sharp shape transition from a spherical shape at N = 58 to a strongly prolate-deformed shape at N = 60
The quest for the shape coexistence and quantum phase transition in shape of Zr isotopes was addressed in many theoretical approaches, including beyond mean-field ones with Gogny and Skyrme forces, the large-scale shell model (LSSM), the Monte Carlo shell model (MCSM), and the algebraic IBM model with configuration mixing; see [1] for a recent review
The shell model approaches are well suited for an accurate description of such changes, provided a large enough model space can be handled numerically; it is usually the intruder orbitals coming down in the neutron-rich nuclei that are the source of necessary quadrupole correlations

Summary

Introduction

The quest for the shape coexistence and quantum phase transition in shape of Zr isotopes was addressed in many theoretical approaches, including beyond mean-field ones with Gogny and Skyrme forces, the large-scale shell model (LSSM), the Monte Carlo shell model (MCSM), and the algebraic IBM model with configuration mixing; see [1] for a recent review. Such rapid shape transitions are challenging for a theoretical description, which has to model to great detail the interplay between the stabilizing role of the shell gaps and the quadrupole correlations tending to deform the nucleus.

Shell Model Framework

Properties of Odd–Even Sr Isotopes

Low-Energy Spectra of Even–Even Sr Isotopes

Collectivity in the Sr Chain towards N = 60

Conclusions