Panity and Time Reversal Test in Very Slow Neutron Reactions

共振区极化慢中子反应是研究核宇称非守恒效应的有效手段，因为在p波共振区的中子激发中发现了宇称非守恒效应的显著增强。为了研究PNC效应如此大幅度增强的原因，我们测量了U、Th、Pd、I、In、Ag等靶的中子反应纵向不对称性，Sb和Cs的中子透射法和γ-实验结果表明，这种大的增强现象并不是只有少数几种情况下才有共振，但它是一个普遍的未来的p波共振。根据复合核的统计观点，在较宽的质量数范围内，确定了弱扩展宽度为10^ eV量级<-7>。这一结果可用s-p混合模型解释，并测量了中子在La靶上透射时的宇称非守恒自旋转动。作为研究中子吸收反应中时间反转破坏的工具，LaAlO_3中La核的动态极化另一方面，在770 K下，用后一束电子束对萘中的质子进行了极化。对称性测量的中子束。

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.