# Quasicontinuum $\gamma$-decay of $^{91,92}$Zr: benchmarking indirect ($n,\gamma$) cross section measurements for the $s$-process

## TL;DR

This study extracts nuclear level densities and gamma-ray strength functions for zirconium isotopes using the Oslo method, providing data that benchmark indirect ($n, extgamma$) cross section measurements relevant for the s-process nucleosynthesis.

## Contribution

It presents new gamma-ray strength functions and nuclear level densities for $^{91,92}$Zr, covering a broad energy range and validating an indirect method for estimating neutron capture cross sections.

## Key findings

- Reproduces known ($n, extgamma$) cross sections for Zr isotopes.
- Identifies structures in gamma-ray strength functions at specific energies.
- Serves as a benchmark for indirect cross section measurement methods.

## Abstract

Nuclear level densities (NLDs) and $\gamma$-ray strength functions ($\gamma$SFs) have been extracted from particle-$\gamma$ coincidences of the $^{92}$Zr($p,p' \gamma$)$^{92}$Zr and $^{92}$Zr($p,d \gamma$)$^{91}$Zr reactions using the Oslo method. The new $^{91,92}$Zr $\gamma$SF data, combined with photonuclear cross sections, cover the whole energy range from $E_{\gamma} \approx 1.5$~MeV up to the giant dipole resonance at $E_{\gamma} \approx 17$~MeV. The wide-range $\gamma$SF data display structures at $E_{\gamma} \approx 9.5$~MeV, compatible with a superposition of the spin-flip $M1$ resonance and a pygmy $E1$ resonance. Furthermore, the $\gamma$SF shows a minimum at $E_{\gamma} \approx 2-3$~MeV and an increase at lower $\gamma$-ray energies. The experimentally constrained NLDs and $\gamma$SFs are shown to reproduce known ($n, \gamma$) and Maxwellian-averaged cross sections for $^{91,92}$Zr using the {\sf TALYS} reaction code, thus serving as a benchmark for this indirect method of estimating ($n, \gamma$) cross sections for Zr isotopes.