Development of Polarized ³He Neutron Spin Filter

Abstract

Development of the neutron spin filter (NSF) based on polarized gaseous ³He is under way at KEK. ³He nuclei have a large neutron absorption cross section depending on the spin direction. A neutron spin filter is possible with polarized ³He nuclei. Gaseous ³He is polarized by the spin exchange optical pumping (SEOP) method. ³He cells made of sapphire and quartz glass have been prepared and tested. Spin relaxation times of more than 100 hours are regularly observed for quartz glass cells. ³He polarizations have been measured with a pulsed neutron beam at KENS to be 63% for a sapphire cell and 54% for a quartz glass cell. With these cells, neutron polarizations of 86% and 74% were obtained, respectively, at thermal energy. In this article, the up-to-date status of the development is reported as well as general properties of the SEOP-NSF.