Improved microscopic nuclear level densities within the Hartree-Fock-Bogoliubov plus combinatorial method

TLDR

The study builds on a microscopic combinatorial model to improve energy‑, spin‑, and parity‑dependent nuclear level densities. The authors compute intrinsic state densities, rotational and vibrational enhancements—including phonon excitations—and generate total and partial level densities for over 8,500 nuclei, extending the method to fission saddle points and radiative neutron capture calculations. The model reproduces experimental s‑ and p‑wave neutron resonance spacings, accurately extrapolates low‑energy level densities, agrees with particle‑γ coincidence data, and provides renormalization factors for nuclei with sufficient experimental information.

Abstract

New developments have been brought to our energy-, spin-, and parity-dependent nuclear level densities based on the microscopic combinatorial model. As in our previous study, a detailed calculation of the intrinsic state density and of the rotational enhancement factor is included, but this time the vibrational contributions explicitly take the phonon excitations into account. The present model predicts the experimental $s$- and $p$-wave neutron resonance spacings with a degree of accuracy comparable to that of the best global models available. It is also shown that the model gives a reliable extrapolation at low energies where experimental data on the cumulative number of levels can be extracted. The predictions are also in good agreement with the experimental data extracted from the analysis of particle-$\ensuremath{\gamma}$ coincidence in the ($^{3}\mathrm{He}$, $\ensuremath{\alpha}\ensuremath{\gamma}$) and ($^{3}\mathrm{He}$, $^{3}\mathrm{He}$${}^{'}\ensuremath{\gamma}$) reactions. Total as well as partial level densities for more than 8500 nuclei are made available in a table format for practical applications. For the nuclei for which experimental $s$-wave spacings and enough low-lying states exist, renormalization factors are provided to reproduce simultaneously both observables. The same combinatorial method is used to estimate the nuclear level densities at the fission saddle points of actinides and at the shape isomer deformation. Finally, the new nuclear level densities are applied to the calculation of radiative neutron capture cross sections.