Measurement of the transverse asymmetry of γ-rays in the ¹¹⁷Sn(n,γ)¹¹⁸Sn reaction

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.