Nuclear temperatures from the evaporation fragment spectra and observed anomalies

TL;DR

This paper investigates evaporation fragment spectra from compound nuclei near A=100, revealing anomalies in the slopes of lithium, beryllium, boron, and carbon spectra that suggest higher residual nucleus temperatures than predicted by standard statistical models.

Contribution

It identifies a slope anomaly in evaporation spectra that standard models cannot explain, indicating a need for quantum mechanical analysis of statistical emissions.

Findings

Alpha spectra agree with statistical model predictions.

Lithium, beryllium, boron, and carbon spectra show gentler slopes.

Anomalies are largest for lithium and decrease with excitation energy.

Abstract

The extreme back-angle evaporation spectra of alpha, lithium, beryllium, boron and carbon from different compound nuclei near A=100 (EX=76-210 MeV) have been compared with the predictions of standard statistical model codes such as 'CASCADE' and 'GEMINI'. It was found that the shapes of the alpha spectra agree well with the predictions of the statistical models. However the spectra of lithium, beryllium, boron and carbon show significantly gentler slopes implying higher temperature of the residual nuclei, even though the spectra satisfy all other empirical criteria of statistical emissions. The observed slope anomaly was found to be largest for lithium and decreases at higher excitation energy. These results could not be understood by adjusting the parameters of the statistical models or from reaction dynamics and might require examining the statistical model from a quantum mechanical perspective.