Researchers from NIST and the Institut Laue Langevin (ILL) collaborated on experiments to study the effects of high flux neutron beams on spin-exchange optical pumping (SEOP). The key finding was that alkali spin relaxation induced by the beam scales with the square root of neutron flux, increasing laser power demands.
The experiments revealed both fast and slow (~300 s) components of beam-induced relaxation, with the slow component potentially linked to nitrogen. However, interpreting the results was complicated by factors like shortened stopping lengths for charged particles at higher nitrogen densities.
The research was published in Phys. Rev. A and Journal of Physics: Conference Series. NIST is developing and testing “double cells” to separate optical pumping and spin filter volumes, potentially bypassing neutron beam issues. These cells have advantages for continuous pumping but require higher laser power.
Understanding neutron beam effects on SEOP will allow exploitation of 3He spin filters for high flux experiments at NIST and other labs, while new cell approaches will benefit continuous optical pumping goals.
Keywords: Neutron, Spin-exchange, Optical pumping, Laser power, Polarization
