Research on a neutron spin rotation caused by the weak interaction

点击翻译按钮获取中文摘要

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.