Angular Distribution of γ-rays from Neutron-Induced Compound States of ¹⁴⁰La

Angular distribution of individual γ-rays, emitted from a neutron-induced compound nuclear state via radiative capture reaction of ¹³⁹La(n,γ) has been studied as a function of incident neutron energy in the epithermal region by using germanium detectors. An asymmetry ALH was defined as (NL − NH)/(NL + NH), where NL and NH are integrals of low and high energy region of a neutron resonance respectively, and we found that ALH has the angular dependence of (A cos θγ + B), where θγ is emitted angle of γ-rays, with A = −0.3881 ± 0.0236 and B = −0.0747 ± 0.0105 in 0.74 eV p-wave resonance. This angular distribution was analyzed within the framework of interference between s- and p-wave amplitudes in the entrance channel to the compound nuclear state, and it is interpreted as the value of the partial p-wave neutron width corresponding to the total angular momentum of the incident neutron combined with the weak matrix element, in the context of the mechanism of enhanced parity-violating effects. Additionally we used the result to quantify the possible enhancement of the breaking of the time-reversal invariance in the vicinity of the p-wave resonance.