Energy-Dependent Angular Distribution Of Individual Gamma Rays In The La-139(N, Gamma) La-140* Reaction

Neutron energy-dependent angular distributions were observed for individual gamma rays from the 0.74 eV p-wave resonance of La-139+n to several lower excited states of La-140. 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. Our results can be interpreted as interference between s- and p-wave amplitudes, which may be used to study discrete symmetries of fundamental interactions.