Energy dependent angular distribution of individual ${\hat{I}}^3$-rays in the ${}^{139}$La($n$, ${\hat{I}}^3$)${}^{140}$La* reaction

Abstract

Neutron energy-dependent angular distributions were observed for individual ${\hat{I}}^3$-rays from the 0.74 eV p-wave resonance of ${}^{139}$La+$n$ to several lower excited states of ${}^{140}$La. The ${\hat{I}}^3$-ray signals were analyzed in a two dimensional histogram of the ${\hat{I}}^3$-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 ${\hat{I}}^3$-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.

6 pages, 7 figures