Angular distribution of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math> rays from the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>p</mml:mi></mml:math>-wave resonance of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Sn</mml:mi><mml:mprescripts/><mml:none/><mml:mn>118</mml:mn></mml:mmultiscripts></mml:math>
J. Koga, S. Takada, S. Endo, H. Fujioka, K. Hirota, K. Ishizaki, A. Kimura, M. Kitaguchi, Y. Niinomi, T. Okudaira, K. Sakai, T. Shima, H. M. Shimizu, Y. Tani, T. Yamamoto, H. Yoshikawa, T. Yoshioka
Abstract
The neutron energy-dependent angular distribution of $\ensuremath{\gamma}$ rays from the $^{117}\mathrm{Sn}(n,\ensuremath{\gamma})$ reaction was measured with germanium detectors and a pulsed neutron beam. The angular distribution was clearly observed in $\ensuremath{\gamma}$-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 $({N}_{\mathrm{L}}\ensuremath{-}{N}_{\mathrm{H}})/({N}_{\mathrm{L}}+{N}_{\mathrm{H}})$, 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 $(Acos{\ensuremath{\theta}}_{\ensuremath{\gamma}}+B)$, where ${\ensuremath{\theta}}_{\ensuremath{\gamma}}$ is the $\ensuremath{\gamma}$-ray emission angle with respect to the incident neutron momentum, with $A=0.394\ifmmode\pm\else\textpm\fi{}0.073$ and $B=0.118\ifmmode\pm\else\textpm\fi{}0.029$ in the 1.33 eV $p$-wave resonance.