Parity and Time Reversal Test in Slow Neutron Absorption

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The interaction of epithermal neutrons with nuclei consists of elastic scattering by optical potential of nuclei and resonance absorption. The compound resonances are well resolved each other in the epithermal energy region, whereas the resonances are overlapped in higher energy region for heavy nuclei. Small contribution of p-wave resonances is observed although s-wave contribution is dominant in the case that the resonances are well resolved. Parity violating effect can be accumulated during the life time of compound resonances. The enhancement of parity-violation is explained as the result of the interference between two opposite parity amplitudes, e.g. s- and p-wave amplitudes. The study of parity-violating enhancement mechanism is very important for possible T-violation experiments.P-violating asymmetries with respect to the helicity of incident neutrons were measured by the neutron transmission method in p-wave resonances of uranium, thorium, indium, silver and niobium at LAMPF, Los Alamos as an International Scientific Research Program.At Los Alamos a longitudinal polarized proton filter which consists of NH_3 beads were used to obtain longitudinally polarized neutron beams. ^<10>B loaded liquid scintillator was used in order to detect neutrons at very high counting rate in the energy region of a few hundred eV.A method to measure the capture gamma-rays was also used to detect small p-wave resonances with sufficient accuracy at Los Alamos. Gamma-ray detectors of CsI, BaF_2 and GSO were constructed and places 60m apart from the neutron source in order to minimize the background from the neutron source.P-violating asymmetries were successfully observed at the level of 10^<-4> in p-wave resonances of various nuclei. The results gave us information on a systematics of the enhancement mechanism which depends upon the nuclear mass number and resonance character.