Measurement of the transverse asymmetry of $\gamma$-rays in the $^{117}$Sn(n,$\gamma$)$^{118}$Sn reaction

TL;DR

This study measures the angular dependence of gamma-ray asymmetries in the $^{117}$Sn(n,$$)$^{118}$Sn reaction to investigate parity-violating effects and their relation to time-reversal invariance breaking in compound nuclei.

Contribution

It provides experimental data on gamma-ray asymmetries in a specific neutron capture reaction, supporting models of parity violation and time-reversal symmetry breaking in nuclear states.

Findings

Observed energy-dependent gamma-ray asymmetries with neutron polarization.

Detected angular dependence of gamma-ray yields related to parity violation.

Supports the mixing model of parity-unfavored amplitudes in compound states.

Abstract

Largely enhanced parity-violating effects observed in compound resonances induced by epithermal neutrons are currently attributed to the mixing of parity-unfavored partial amplitudes in the entrance channel of the compound states. Furthermore, it is proposed that the same mechanism that enhances the parity-violation also enhances the breaking of time-reversal-invariance in the compound nucleus. The entrance-channel mixing induces energy-dependent spin-angular correlations of individual $\gamma$-rays emitted from the compound nuclear state. For a detailed study of the mixing model, a $\gamma$-ray yield in the reaction of $^{117}$Sn(n,$\gamma$)$^{118}$Sn was measured using the pulsed beam of polarized epithermal neutrons and Ge detectors. An angular dependence of asymmetric $\gamma$-ray yields for the orientation of the neutron polarization was observed.