Energy-dependent angular distribution of individual <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>γ</mml:mi></mml:math> rays in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>La</mml:mi><mml:mprescripts/><mml:none/><mml:mn>139</mml:mn></mml:mmultiscripts><mml:mrow><mml:mo>(</mml:mo><mml:mi>n</mml:mi><mml:mo>,</mml:mo><mml:mi>γ</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mover><mml:mmultiscripts><mml:mi>La</mml:mi><mml:mprescripts/><mml:none/><mml:mn>140</mml:mn></mml:mmultiscripts><mml:mo>*</mml:mo></mml:mover></mml:mrow></mml:math> reaction
Takuya Okudaira, Shunsuke Endo, Hiroyuki Fujioka, K. Hirota, Kohei Ishizaki, A. Kimura, Masaaki Kitaguchi, Jun Koga, Y. Niinomi, K. Sakai, Tatsushi Shima, Hirohiko M. Shimizu, S. Takada, Y. Tani, Tomoki Yamamoto, H. Yoshikawa, T. Yoshioka
Abstract
Neutron energy-dependent angular distributions were observed for individual $\ensuremath{\gamma}$ rays from the 0.74 eV $p$-wave resonance of $^{139}\mathrm{La}+n$ to several lower excited states of $^{140}\mathrm{La}$. The $\ensuremath{\gamma}$-ray signals were analyzed in a two-dimensional histogram of the $\ensuremath{\gamma}$-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 $\ensuremath{\gamma}$ 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.