Panity and Time Reversal Test in Very Slow Neutron Reactions

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Polarized slow neutron reactions on nuclei in the resonance region are useful to investigate parity nonconservation (PNC) effect in nuclei, since large enhancement of PNC effect has been found in neutron absorptions on p-wave resonances. In order to study the origin of such large enhancement of the PNC effect, the longitudinal asymmetries in the neutron reactions have been measured for the targets of U, Th, Pd, I, In, Ag, Sb and Cs by means of a neutron transmission method and a gamma-ray detection method in the energy region of 1 eV to 350 eV at LANSCE.The experiment shows that the large enhancement is not the phenomena only for few resonances but is a prevalent fuature of p-wave resonances. Based on the statistical view of the compound nucleus, the weak spreading width GAMMAw has been determined to be the order of 10^<-7> eV in the wide range of mass number. The result can be explained by the s-p mixing model for the enhancement of PNC.The parity nonconserving spin rotation in neutron transmission on a La target has also been measured. The result on the p-wave resonance is found to be consistent with the results of helicity asymmetries.As a tool to study-time-reversal violation in neutron absorption reaction, the dynamic polarization of La nuclei in LaAlO_3 has been carried out successfully in a dilution refrigeratorOn the other hand the proton in naphthalene doped with pentacene has been polarized using a later beam at 770K It will be useful to make polarized neutron beams for symmetry measurements.