[RBRC seminar] Statistical Properties of Actinides from Shell Model Monte-Carlo

by Dr Dallas DeMartini (BNL)

Thursday 29 Jan 2026, 12:30 → 14:30 US/Eastern

2-160 (https://bnl.zoomgov.com/j/1600983728?pwd=RAD7OLcqre7Ycsp6JfFp6HAnpyLxex.1)

Microscopic calculations of nuclear properties in the presence of correlations pose a challenging many-body problem. The configuration-interaction shell model provides a suitable framework for the inclusion of correlations, but the large dimensionality of the many-particle model space has hindered its application in heavy nuclei, often necessitating the use of approximations such as mean-field methods or density functional approaches. The shell-model Monte Carlo (SMMC) method, which is based on the Hubbard-Stratonovich transformation, enables calculations in model spaces that are many orders of magnitude larger than can be treated by direct diagonalization methods.

We have recently extended the SMMC method to the actinides. The actinides present several technical challenges compared with the lanthanides: the required valence single-particle model space is larger, and the lower first excitation energy requires larger values of the imaginary time (or inverse temperature) to compute the ground-state properties of these nuclei. In order to study these nuclei, we have developed phenomenological good-sign interactions for use in single-particle model spaces as large as 10^32, which is 20 orders of magnitude larger than the largest space used in conventional shell-model calculations.

In this seminar, I will first introduce the conventional shell-model picture and discuss the differences of the SMMC method. I will discuss novel techniques used for calculations and present new results for key properties of actinides. I will show that our methods produce nuclear level densities that are in excellent agreement with recent Oslo method experiments and have enabled the first theoretical predictions that the so-called 'low-energy enhancement' persists in the gamma-ray strength functions of actinides. I will also present ongoing investigations into the quadrupole shape distributions of these actinides. These observables have applications as inputs in calculations of astrophysical reaction rates, nuclear fission, and relativistic heavy-ion collisions.