Parity and Time Reversal Test in Slow Neutron Absorption

超热中子与原子核的相互作用包括原子核光学势的弹性散射和共振吸收。在超热能区，复合共振能很好地相互分辨，而在高能区，重核的复合共振相互重叠。p波共振的小的贡献被观察到，虽然s波的贡献是占主导地位的情况下，共振被很好地解决。宇称破坏效应可以在复合共振态的寿命期间累积。宇称破坏的增强被解释为两个相反的宇称振幅之间的干扰的结果，例如S波和P波振幅。宇称破缺增强机制的研究对于T破缺实验具有重要意义，在LAMPF上用中子透射法测量了铀、钍、铟、银和铌的p波共振中P破缺不对称性与入射中子螺旋度的关系，洛斯阿拉莫斯国家实验室作为一个国际科学研究计划，在洛斯阿拉莫斯国家实验室研制了一种纵向极化质子过滤器，3珠用于获得纵向极化中子束。为了<10>在几百eV的能量范围内以非常高的计数率探测中子，使用了装载有^ B的液体闪烁体。在洛斯阿拉莫斯，还使用了测量俘获γ射线的方法来探测具有足够精度的小p波共振。在距中子源60m处安装了CsI、BaF_2和GSO γ射线探测器，以减小中子源的本底，成功地观测到不同核的p波共振在10 μ s水平上的P破坏不对称<-4>性。结果给我们提供了一个系统的增强机制，这取决于核的质量数和共振特性的信息。

The interaction of epithermal neutrons with nuclei consists of elastic scattering by optical potential of nuclei and resonance absorption. The compound resonances are well resolved each other in the epithermal energy region, whereas the resonances are overlapped in higher energy region for heavy nuclei. Small contribution of p-wave resonances is observed although s-wave contribution is dominant in the case that the resonances are well resolved. Parity violating effect can be accumulated during the life time of compound resonances. The enhancement of parity-violation is explained as the result of the interference between two opposite parity amplitudes, e.g. s- and p-wave amplitudes. The study of parity-violating enhancement mechanism is very important for possible T-violation experiments.P-violating asymmetries with respect to the helicity of incident neutrons were measured by the neutron transmission method in p-wave resonances of uranium, thorium, indium, silver and niobium at LAMPF, Los Alamos as an International Scientific Research Program.At Los Alamos a longitudinal polarized proton filter which consists of NH_3 beads were used to obtain longitudinally polarized neutron beams. ^<10>B loaded liquid scintillator was used in order to detect neutrons at very high counting rate in the energy region of a few hundred eV.A method to measure the capture gamma-rays was also used to detect small p-wave resonances with sufficient accuracy at Los Alamos. Gamma-ray detectors of CsI, BaF_2 and GSO were constructed and places 60m apart from the neutron source in order to minimize the background from the neutron source.P-violating asymmetries were successfully observed at the level of 10^<-4> in p-wave resonances of various nuclei. The results gave us information on a systematics of the enhancement mechanism which depends upon the nuclear mass number and resonance character.