Demonstration of the use of polarised 3He as a broadband polariser on a pulsed time-of-flight neutron source

Abstract We discuss the use of a new test beamline on the ISIS time-of-flight neutron source where the pressure, polarisation and relaxation time of spin-polarised 3 He neutron spin filter (NSF) cells can be determined. The beamline consists of a 3 He cell held in a magnetostatic cavity and a 3 He monitor in which the change in neutron transmission due to the highly spin-dependent cross-section of 3 He is measured. The neutron polarisation is simultaneously confirmed using the asymmetry method, through the use of a Heusler crystal analyser and Mezei flipper. The beamline is routinely used in the characterisation of 3 He (NSF) cells and polarisations of up to 70% in sealed spin exchange optically pumped cells have been measured using both techniques.