Lifetime behaviour and polarization stability in 3He neutron spin filter cells

Abstract

The successful use of 3He cells in polarized neutron applications demands that once polarized the gas has both a long relaxation time and high polarization. In spin-exchange optical pumping the cell characteristics determine the maximum polarization as well as the lifetime.We report on our experience of neutron spin filter cells, showing results on the orientation dependence of such cells. We observe a previously observed lifetime hysterisis effect in 3He cell relaxation lifetime and include new measurements of the angular dependence of the relaxation lifetime, that are characteristic of a dipolar effect which diminishes upon repeated pumping/cooling cycles. We present demonstrations of magnetization effects in 3He and 129Xe cells and show the applicability of using sol-gel coatings on reducing the magnetization effect in 129Xe cells.We report recent results of the stability of the polarization in new SEOP cells, which was evident for 2 states, one with high energy spin state, low T1 orientation and the second with low energy spin state, high T1 orientation. These results are suggestive of an abnormal relaxation and have only been observed for cells with short (T1 <10 Hours) lifetimes.