Examination of level density prescriptions in the interpretation of high energy gamma-ray spectra

TL;DR

This study compares different level density models to interpret high energy gamma-ray spectra from various compound nuclei, finding that only the IST prescription consistently explains the data across different excitation energies and spins.

Contribution

It evaluates three level density prescriptions in the context of high energy gamma-ray spectra analysis, identifying the IST model as the most effective across multiple nuclei.

Findings

Only the IST prescription explains the spectra for all nuclei.

Shell effects are significant at low excitation energies.

Shell effects melt at high excitation energies, affecting model accuracy.

Abstract

High energy $\gamma$-ray spectra measured by our group involving the compound nuclei (CN) $^{63}$Cu at excitation energy ($E^*$) $\sim$ 36 MeV with average angular momentum ($J$) = 12 - 17 $\hbar$, $^{97}$Tc at $E^* \sim$ 29 - 50 MeV with $J$ = 12 - 14 $\hbar$, $^{113}$Sb at $E^*$ = 109 MeV and 121 MeV with $J$ = 49 - 59 $\hbar$ and $^{201}$Tl at $E^*$ = 39.5, 47.5 MeV with $J$ = 18 - 24 $\hbar$ have been analyzed utilizing the level density prescriptions of (i)Ignatyuk, Smirenkin and Tishin (IST), (ii)Budtz-Jorgensen and Knitter (BJK), and (iii) Kataria, Ramamurthy and Kapoor (KRK). These three prescriptions have been tested for correct statistical model description of high energy $\gamma$-rays in the light of extracting the giant dipole resonance (GDR) parameters at low excitation energy and spin where shell effects might play an important role as well as at high excitation energy where shell effects have melted. Interestingly, only the IST level density prescription could explain the high energy $\gamma$-ray spectra with reasonable GDR parameters for all the four nuclei.