Panity and Time Reversal Test in Very Slow Neutron Reactions

共振区原子核上的极化慢中子反应有助于研究原子核中的宇称非守恒(PNC)效应，因为在P波共振的中子吸收中发现了PNC效应的显著增强。为了研究PNC效应增强如此大的原因，在LANSCE上用中子透射法和伽马射线探测方法测量了U、Th、Pd、I、In、Ag、Sb和Cs靶在1 eV到350 eV能区中子反应的纵向不对称性。实验表明，这种大的增强不只是少数共振的现象，而是一种普遍存在的p波共振的未来。根据复合核的统计观点，确定在较宽的质量数范围内，弱扩散宽度GAMMAw为10^~(-7)eV量级。这一结果可以用增强PNC的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旋转。作为研究中子吸收反应中时间反转破坏的工具，LaAlO_3中La原子核的动态极化已在稀释式制冷机中成功地实现。另一方面，在770K用后束极化了掺并五苯的萘中的质子，这将有助于制作用于对称性测量的偏振中子束。

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.