Total and partial cross sections of the $^{112}$Sn($\alpha,\gamma$)$^{116}$Te reaction measured via in-beam $\gamma$-ray spectroscopy

TL;DR

This study measured total and partial cross sections of the $^{112}$Sn($ extalpha$,γ)$^{116}$Te reaction using in-beam γ-ray spectroscopy at sub-Coulomb energies, and compared results with Hauser-Feshbach calculations to refine nuclear models.

Contribution

It provides new experimental cross-section data and demonstrates the necessity of local modifications to optical model potentials for accurate theoretical predictions.

Findings

Measured cross sections at four energies between 10.5 and 12 MeV.

Good agreement with previous activation data validates the in-beam method.

Modified optical model potentials improve the match between theory and experiment.

Abstract

An extended database of experimental data is needed to address uncertainties of the nuclear-physics input parameters for Hauser-Feshbach calculations. Especially $\alpha$+nucleus optical model potentials at low energies are not well known. The in-beam technique with an array of high-purity germanium (HPGe) detectors was successfully applied to the measurement of absolute cross sections of an ($\alpha$,$\gamma$) reaction on a heavy nucleus at sub-Coulomb energies. The total and partial cross-section values were measured by means of in-beam $\gamma$-ray spectroscopy. Total and partial cross sections were measured at four different $\alpha$-particle energies from $E_\alpha = 10.5$ MeV to $E_\alpha = 12$ MeV. The measured total cross-section values are in excellent agreement with previous results obtained with the activation technique, which proves the validity of the applied method. The experimental data was compared to Hauser-Feshbach calculations using the nuclear reaction code TALYS. A modified version of the semi-microscopic $\alpha$+nucleus optical model potential OMP 3, as well as modified proton and $\gamma$ widths, are needed in order to obtain a good agreement between experimental data and theory. It is found, that a model using a local modification of the nuclear-physics input parameters simultaneously reproduces total cross sections of the $^{112}$Sn($\alpha$,$\gamma$) and $^{112}$Sn($\alpha$,p) reactions. The measurement of partial cross sections turns out to be very important in this case in order to apply the correct $\gamma$-ray strength function in the Hauser-Feshbach calculations. The model also reproduces cross-section values of $\alpha$-induced reactions on $^{106}$Cd, as well as of ($\alpha$,n) reactions on $^{115,116}$Sn, hinting at a more global character of the obtained nuclear-physics input.