Indirect measurement of the $\pmb{(n,\gamma)^{127}}$Sb cross section

TL;DR

This paper presents an indirect experimental approach to determine the neutron capture cross section of $^{126}$Sb, crucial for understanding the i-process in nucleosynthesis, by extracting nuclear level density and gamma-ray strength functions using the Oslo method.

Contribution

It introduces an indirect measurement technique for the $^{126}$Sb(n,gamma) cross section using the Oslo method, providing data that constrains reaction rates relevant to astrophysics.

Findings

Level density agrees with known discrete levels at low energies.

Gamma-ray strength function shows an upbend and possible pygmy structure.

Experimental cross section aligns with some nuclear data libraries but differs from ENDF/B-VIII.0.

Abstract

Nuclei in the $^{135}$I region have been identified as being a possible bottleneck for the \textit{i} process. Here we present an indirect measurement for the Maxwellian-averaged cross section of $^{126}\text{Sb}(n,\gamma)$. The nuclear level density and the $\gamma$-ray strength function of $^{127}$Sb have been extracted from $^{124}$Sn$(\alpha,p\gamma)^{127}$Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higher-excitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between $E_\gamma\approx$ 1.5-8.0 MeV presents several features, such as an upbend and a possibly double-peaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code TALYS seem to reproduce the experimental data. The Maxwellian-averaged cross section for the $^{126}$Sb$(n,\gamma)^{127}$Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to TALYS. We observe a good agreement with the JINA REACLIB, TENDL, and BRUSLIB libraries, while the ENDF/B-VIII.0 library predicts a significantly higher rate than our results.