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Parity and Time Reversal Test in Slow Neutron Absorption

慢中子吸收中的宇称和时间反转测试

基本信息

批准号：
04044082
负责人：
MASAIKE Akira
金额：
$ 3.71万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

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.

超热中子与原子核的相互作用包括原子核光势的弹性散射和共振吸收。在低温能区，复合共振可以很好地相互分辨，而在高能区，重核的复合共振是重叠的。纵波共振的贡献很小，尽管在共振被很好地解决的情况下，s波贡献占主导地位。宇称违反效应可以在复合谐振的寿命期间累积。宇称违反的增强被解释为两个相反的宇称幅值，例如s波和p波幅值之间的干涉的结果。奇偶违反增强机制的研究对可能的t违反实验具有重要意义。在美国洛斯阿拉莫斯国家实验室LAMPF，用中子透射法测量了铀、钍、铟、银和铌的p波共振中入射中子的违反p的不对称性。在洛斯阿拉莫斯国家实验室，采用由NH_3微珠组成的纵向极化质子滤光器来获得纵向极化中子束。^<10 b> B负载的液体闪烁体用于在几百eV能量区域以非常高的计数率探测中子。在洛斯阿拉莫斯，一种测量捕获伽马射线的方法也被用来以足够的精度探测小的p波共振。建造了CsI、BaF_2和GSO的伽玛射线探测器，并将其放置在距离中子源60m处，以减小中子源的背景辐射。在10^<-4>的水平上成功地观察到各种核的p波共振的违反p的不对称性。这些结果为我们提供了依赖于核质量数和共振特性的系统增强机制的信息。