Parity and Time Reversal Invariance Test in Very Slow Neutron Reactions

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In order to study the origin of large enhancement of the parity violation effect in neutron resonance absorption reactions, the longitudinal asymmetries in p-wave resonances have been measured for In, Ag, Pd, Sb, Cs, Xe, Th and U targets in the energy region of 1 eV to 350 eV.We constructed a polarized proton filter for polarizing the neutron beam, and a spin flipper to reverse the diection of neutron spin. We used also liquid scintillator arrays as a neutron detector. A new computer code in which multi-level formula is used to calculate the neutron cross section has been developed.We have found 47 p-wave resonances which have large helicity asymmetries with the statistical significance greater than 3δ. The signs of the asymmetries have been found to random. The experiment shows that the large enhancement of parity violating effect is a prevalent feature of p-wave resonances. The weak spreading widths of nuclei (ΓィイD2wィエD2) have been determined from the experimental values of asymmetries . The obtained ΓィイD2wィエD2's agree with estimated value based on the statistical view.Furthermore, we have polarized protons in naphthalene crystals doped with pentacene using a dye laser at the temperature higher than 77 Kelvin. Such a polarized proton target can be used to obtain polarized neutrons.We obtained 50% polarization of La nuclei in mono-crystal of LaAloィイD23ィエD2 by means of the dynamic polarization method. The polarized La target will be of vital importance for the measurement of time reversal violation in the neutron resonance absorption.