New level density parameter beyond Egidy-Bucurescu's systematics

TL;DR

This paper extends the systematics of nuclear level density parameters beyond Egidy-Bucurescu, fitting new models and comparing their performance to existing parameters, with implications for theoretical calculations of transitional nuclei.

Contribution

It introduces new global level density parameters fitted with different models that outperform some existing parameters in statistical calculations.

Findings

New LDM-type parameters outperform Toke-Swiatecki parameters.

Reisdorf parameters show the best overall performance.

Power-law A-dependence parameters perform better than existing ones.

Abstract

Extending beyond the Egidy-Bucurescu systematics, the nuclear level density parameters (LDPs) for the back-shifted Fermi gas model were compiled. Three forms of LDPs were fitted: the liquid-drop model (LDM), the droplet model (DM), and the power-law dependence on mass number A. Additionally, the root-mean-square deviations (RMSDs) of the new LDPs and existing literature values were calculated. The newly fitted global LDM-type parameters outperform the commonly used Toke-Swiatecki parameters in various statistical model calculations. In contrast, neither the global nor the combined DM-type parameters yielded satisfactory results. Among the tested parameter sets, the widely adopted Reisdorf parameters exhibited the best overall performance, as evidenced by the larger number of experimental data points falling within their narrower RMSD confidence intervals. For the power-law A-dependence, the new global parameters performed better than the existing homogeneous ones. The ground-state deformation and isospin correction factors had minimal overall impact on the LDP fits. However, the current results suggest that theoretical calculations for transitional nuclei should account for ground-state deformation effects.