Suppression of Excited-State Contributions to Stellar Reaction Rates

TL;DR

This paper re-evaluates the suppression of stellar enhancement factors in nuclear reactions, emphasizing ground-state contributions over SEFs, and identifies numerous exceptions to the Q-value rule, refining understanding of reaction rate contributions.

Contribution

It introduces an improved method focusing on ground-state contributions to assess excited-state effects, updating previous tables and expanding the known exceptions to the Q-value rule.

Findings

2350 reactions show larger ground-state contributions in the endothermic direction.

The Coulomb suppression effect is confirmed but with more exceptions.

Large variations in ground-state contributions often do not significantly change SEFs.

Abstract

It has been shown in previous work [Phys. Rev. Lett. 101, 191101 (2008); Phys. Rev. C 80, 035801 (2009)] that a suppression of the stellar enhancement factor (SEF) occurs in some endothermic reactions at and far from stability. This effect is re-evaluated using the ground-state contributions to the stellar reaction rates, which were shown to be better suited to judge the importance of excited state contributions than the previously applied SEFs. An update of the tables shown in Phys. Rev. C 80, 035801 (2009) is given. The new evalution finds 2350 cases (out of a full set of 57513 reactions) for which the ground-state contribution is larger in the reaction direction with negative reaction Q-value than in the exothermic direction, thus providing exceptions to the commonly applied Q-value rule. The results confirm the Coulomb suppression effect but lead to a larger number of exceptions than previously found. This is due to the fact that often a large variation in the g.s. contribution does not lead to a sizeable change in the SEF. On the other hand, several previously identified cases do not appear anymore because it is found that their g.s. contribution is smaller than inferred from the SEF.