Panity and Time Reversal Test in Very Slow Neutron Reactions

由于在p波共振的中子吸收中发现了宇称不守恒效应的显著增强，因此在共振区原子核上的极化慢中子反应对研究原子核中的宇称不守恒效应是有用的。为了研究PNC效应如此大幅度增强的原因，在LANSCE上用中子透射法和伽马射线检测法测量了U、Th、Pd、I、In、Ag、Sb和Cs靶在1 ~ 350 eV能量范围内的中子反应的纵向不对称性。实验表明，大的增强不是少数共振的现象，而是p波共振的一个普遍的未来。根据复合核的统计观点，确定了弱扩散宽度GAMMAw在较宽的质量数范围内为10^<-7> eV数量级。这一结果可以用s-p混合模型来解释。还测量了中子在La靶上传输时的宇称非守恒自旋。p波共振的结果与螺旋不对称的结果是一致的。作为研究中子吸收反应中时间反转违逆的工具，我们在LaAlO_3中成功地进行了La核的动态极化。另一方面，在770K下，用后射束对掺并五苯的萘中的质子进行了极化，这将有助于制作偏振中子束用于对称测量。

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.