A reanalysis of radioisotope measurements of the $^9$Be$(\gamma,n)^8$Be cross-section

TL;DR

This paper reanalyzes radioisotope measurements of the $^9$Be$( abla,n)^8$Be reaction cross-section, resolving previous contradictions and providing precise parameters for the near-threshold $1/2^+$ state, which impacts astrophysics and nuclear theory.

Contribution

It offers a high-accuracy reanalysis of existing measurements, clarifying the properties of the $1/2^+$ state and excluding the virtual state with high confidence.

Findings

Precise parameters for the $1/2^+$ state: $E_R=1738.8 ext{ keV}$, $ ext{Gamma}_ ext{gamma}=0.771 ext{ eV}$, $ ext{Gamma}_n=268 ext{ keV}$.

Contradictions in previous measurements are resolved, improving cross-section data.

Virtual $1/2^+$ state is excluded with 99.3% confidence.

Abstract

The $^9$Be$(\gamma,n)^8$Be reaction is enhanced by a near threshold $1/2^+$ state. Contradictions between existing measurements of this reaction cross-section affect calculations of astrophysical r-process yields, dark matter detector calibrations, and the theory of the nuclear structure of $^9$Be. Select well-documented radioisotope $^9$Be$(\gamma,n)$ source yield measurements have been reanalyzed, providing a set of high-accuracy independently measured cross sections. A Breit-Wigner fit of these corrected measurements yields $E_R=1738.8\pm1.9$ keV, $\Gamma_\gamma=0.771\pm0.021$ eV, and $\Gamma_n=268\pm15$ keV for the $1/2^+$ state. A virtual $1/2^+$ state is excluded with 99.3\% confidence.