Optimised adiabatic fast passage spin flipping for 3He neutron spin filters

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized He-3 used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the He-3 nuclei the polarization of a neutron beam can be efficiently reversed allowing for the transmission of a neutron beam polarized in either spin state. Using an amplitude modulated frequency sweep lasting 500 ms we can spin flip a polarized He-3 neutron spin filter with only 1.8 x 10(-5) loss in He-3 polarization. The small magnetic fields (10-15 G) used to house neutron spin filters mean the He-3 resonant frequencies are low enough to be generated using a computer with a digital 110 card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using He-3 neutron spin filters and polarization losses can be minimised by adjusting sweep parameters. (C) 2010 Elsevier B.V. All rights reserved.