Energy dependent angular distribution of individual $\gamma$-rays in the $^{139}$La($n$, $\gamma$)$^{140}$La* reaction

TL;DR

This study investigates how the angular distribution of gamma rays emitted in the $^{139}$La(n,γ)$^{140}$La* reaction varies with neutron energy, revealing interference effects that could shed light on fundamental symmetries.

Contribution

It provides the first detailed measurement of neutron energy-dependent angular distributions of individual gamma rays in this reaction, highlighting interference between s- and p-wave amplitudes.

Findings

Angular distributions vary with neutron energy.

Interference between s- and p-wave amplitudes observed.

Potential implications for studying fundamental symmetries.

Abstract

Neutron energy-dependent angular distributions were observed for individual $\gamma$-rays from the 0.74 eV p-wave resonance of $^{139}$La+$n$ to several lower excited states of $^{140}$La. The $\gamma$-ray signals were analyzed in a two dimensional histogram of the $\gamma$-ray energy, measured with distributed germanium detectors, and neutron energy, determined with the time-of-flight of pulsed neutrons, to identify the neutron energy dependence of the angular distribution for each individual $\gamma$-rays. The angular distribution was also found for a photopeak accompanied with a faint p-wave resonance component in the neutron energy spectrum. Our results can be interpreted as interference between s- and p-wave amplitudes which may be used to study discrete symmetries of fundamental interactions.