Research on a neutron spin rotation caused by the weak interaction

在弱相互作用引起的中子自旋实验中，将核靶中的自旋角投影到自旋保持场的方向上，然后用极化氦-3滤光器对其进行分析。1993年，为了研究中子自旋处理，进行了初步实验。用极化中子轰击镧靶，测量了p波共振中自旋的角度。由于弱相互作用，初步结果与宇称混合理论一致，但仍存在一定的系统误差，必须加以减小才能得到最终结果。特别是保证中子自旋输运系统与磁分离靶系统之间跃迁的非绝热性是非常重要的。为此，设计了一种新型的自旋固定线圈。用铌板和氦低温恒温器制作了超导箱。为了进一步减小实验误差，1994财年对自旋输运系统和氦-3过滤器进行了改进。中子自旋必须在轰击前绝热地从束流方向旋转到垂直方向。在运输线上有一些绝热系数很低的点。为了保证这些点的绝热性，改进了过渡线圈。自旋角测量的灵敏度取决于氦-3滤光片的偏振。极化的大小几乎取决于作为氦-3气体容器的玻璃电池材料、制造方法和表面清洁方法。近年来，该清洗方法得到了发展，既保证了高质量的玻璃电池的可靠性，又降低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.