Impact of alternative transmission coefficient parameterizations on Hauser-Feshbach theory

TL;DR

This paper compares various formulations of the transmission coefficient in Hauser-Feshbach theory, analyzing their effects on neutron resonance predictions and exploring the potential role of superradiance in nuclear reactions.

Contribution

It introduces a comparative analysis of different transmission coefficient parameterizations, including Moldauer's sum rule and the Moldauer-Simonius form, in the context of Hauser-Feshbach theory.

Findings

Different formulations yield consistent neutron transmission coefficients in resonance regions.

Some approaches predict average resonance parameters without measured resonances.

Superradiance may be a common phenomenon in nuclear collisions, previously overlooked.

Abstract

We investigate different formulations of the transmission coefficient $T_c$, including the form implied by Moldauer's ``sum rule for resonance reactions'' [P.A. Moldauer, Phys. Rev. Lett. 19, 1047 (1967)], the SPRT method [G. Noguere, et al. EPJ Web Conf. 146, 02036 (2017)] and the Moldauer-Simonius form [M. Simonius, Phys. Lett. 52B, 279 (1974); P.A. Moldauer, Phys. Rev. 157, 907 (1967)]. Within these different formulations, we compute the neutron transmission coefficients in the resolved and unresolved resonance regions, allowing a direct comparison with the transmission coefficients computed using an optical model potential. For nuclei for which there are no measured resonances, these approaches allow one to predict the average neutron resonance parameters directly from the optical model and level densities. Some of the approaches are valid in both the strong and weak coupling limits (i.e., any value of the average width and mean level spacing). Finally, both the Moldauer-Simonius and Moldauer's Sum Rule forms approaches suggest that superradiance, that is, the quantum chaotic enhancement of certain channels, may be a common phenomena in nuclear collisions. Our results suggest why superradiance has been previously overlooked. We apply our approach to neutron reactions on the closed shell $^{90}$Zr nucleus and the mid-shell $^{197}$Au nucleus.