Effects of high intensity neutron flux on in-situ spin-exchange optical pumping of 3He

Prior studies revealed neutron beam-induced alkali-metal spin relaxation in He cells polarized in-situ by spin-exchange optical pumping. These effects are minor for neutron beams of low to moderate intensity, but become important at the highest neutron flux levels available in the full spectrum beams of high flux neutron sources. It was found that the relaxation consisted of a fast and a slow component, but the origin of neither is understood. This work further explored the mechanisms of this effect by measuring the magnitude and time dependence of alkali-metal spin-relaxation rates as a function of N2 and He composition. The experiments were performed on a thermal neutron beam line at the Institut Laue-Langevin with a maximum neutron flux of 2.4×109 cm−2 s−1.