Angular distribution of ${\hat{I}}^3$ rays from the p-wave resonance of ${}^{118}$Sn

Abstract

The neutron energy-dependent angular distribution of ${\hat{I}}^3$ rays from ${}^{117}\mathrm{Sn}(n,{\hat{I}}^3)$ reaction was measured with germanium detectors and a pulsed neutron beam. The angular distribution was clearly observed in ${\hat{I}}^3$-ray emissions with an energy of 9327 keV which corresponds to the transition from a neutron resonance of ${}^{117}\mathrm{Sn}+n$ to the ground state of ${}^{118}\mathrm{Sn}$. The angular distribution causes an angular-dependent asymmetric resonance shape. An asymmetry $A_{\mathrm{LH}}$ was defined as $(N_{\mathrm{L}}-N_{\mathrm{H}})/(N_{\mathrm{L}}+N_{\mathrm{H}})$, where $N_{\mathrm{L}}$ and $N_{\mathrm{H}}$ are integrated values for lower- and higher-energy regions of a neutron resonance, respectively. We found that the $A_{\mathrm{LH}}$ has the angular dependence of $(A\cos \hat{I}{¸}_{\hat{I}}^3+B)$, where $\hat{I}{¸}_{\hat{I}}^3$ is the ${\hat{I}}^3$-ray emission angle with respect to the incident neutron momentum, with $A=0.394\pm 0.073$ and $B=0.118\pm 0.029$ in the 1.33 eV p-wave resonance.

5 pages, 5 figures