Research on a neutron spin rotation caused by the weak interaction

在弱相互作用引起的中子自旋转动实验中，将核靶中的自旋转动角投影到自旋保持场的方向上，然后用极化氦3滤波器进行分析。在1993年，为了研究中子自旋处理，进行了初步实验。在该实验中，将极化中子轰击到镧靶中，并测量p波共振中的自旋旋转角。虽然由于弱相互作用，初步结果与宇称混合理论是一致的，但仍存在一些系统误差，必须减小这些误差以获得最终结果。特别是，重要的是确保中子自旋输运系统和磁性分离的靶系统之间的过渡的非绝热性。为此，设计了一种新型的自旋保持线圈。还制作了铌板超导箱和氦低温恒温器。为了进一步减小实验误差，1994财政年度对自旋输运系统和氦-3过滤器进行了改进。在轰击前，中子自旋必须从束流方向旋转到垂直方向。沿运输线沿着有绝热性差的点。为了确保在这些点处的绝热性，改进了过渡线圈。自旋旋转角测量的灵敏度取决于氦-3过滤器的极化，极化的大小主要取决于氦-3气体容器玻璃盒的材料、制造方法和表面清洗方法。近来，已经开发了清洁方法，使得能够以高可靠性提供高质量的玻璃单元，并且减少了中子自旋分析系统的统计误差。

In an experiment for a neutron spin rotation caused by the weak interaction, a spin rotation angle in a nucleat targer is projected to the direction of a spin holding field and then analyzed by a polarized helium-3 filter. In Fy 1993, preliminary experiment was performed in order to investigate a neutron spin handling. A polarized neutron was bombarded into a lanthanum target and an angle of a spin rotation in a p-wave resonance was measured in this experiment. Although the preliminary result was consistent with the theory of parity mixing due to the weak interaction, there remained some systematic errors which must be reduced to obtain final results. Especially, it is important to ensure non-adiabaticity of the transition between a neutron spin transport system and a target system which is separated magnetically. For this purpose, a new coil for spin holding was designed. A super conducting box made of niobium plates and a helium cryostat were constructed as well. Aiming at more reduction of the experimental error, the spin transport system and the helium-3 filter were improved in FY 1994. A neutron spin must be rotated from the beam direction to the perpendicular direction adiabatically just before bombardment. There were some points where the adiabaticity was poor along the transport line. In order to ensure the adiabaticity at such points, a transition coil was improved. A sensitivity of the measurement of the spin rotation angle depends on the polarization of the helium-3 filter.The magnitude of the polarization is almost determined by a material for glass cell as a container of helium-3 gas and methods of fabrication and surface cleaning. Recently, the cleaning method has been developed so that a glass cell with high quality was able to be supplied with high reliability and a statistical error of the neutron spin analyzing system was reduced.