Microsopic nuclear level densities by the shell model Monte Carlo method

TL;DR

This paper discusses the shell model Monte Carlo method for calculating nuclear level densities, especially in heavy nuclei, and introduces a deformation-based approach to improve these calculations.

Contribution

It presents recent advances in the SMMC method for level densities and proposes a new way to incorporate deformation effects into these calculations.

Findings

SMMC enables level density calculations in large model spaces.

Distribution of the axial quadrupole operator indicates deformation.

Deformation-based methods improve level density estimates.

Abstract

The configuration-interaction shell model approach provides an attractive framework for the calculation of nuclear level densities in the presence of correlations, but the large dimensionality of the model space has hindered its application in mid-mass and heavy nuclei. The shell model Monte Carlo (SMMC) method permits calculations in model spaces that are many orders of magnitude larger than spaces that can be treated by conventional diagonalization methods. We discuss recent progress in the SMMC approach to level densities, and in particular the calculation of level densities in heavy nuclei. We calculate the distribution of the axial quadrupole operator in the laboratory frame at finite temperature and demonstrate that it is a model-independent signature of deformation in the rotational invariant framework of the shell model. We propose a method to use these distributions for calculating level densities as a function of intrinsic deformation.