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

• Published in: Physica. B, Condensed matter Condensed matter, 2011-06, Vol.406 (12), p.2436-2438
• Main Authors: McKetterick, T.J., Boag, S., Stewart, J.R., Frost, C.D., Skoda, M.W.A., Parnell, S.R., Babcock, E.
• Format: Article
• Language: English
• Subjects: Adiabatic fast passage; Adiabatic flow; AFP; Atom and neutron optics; Cards; Classical and quantum physics: mechanics and fields; Condensed matter; Digital; Exact sciences and technology; Magnetic fields; Matter waves; Neutron beams; Neutron spin filter; NMR; Physics; Polarization; Polarized neutrons; Waveforms
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/j.physb.2010.11.088

We describe here a method of performing adiabatic fast passage (AFP) spin flipping of polarized 3He used as a neutron spin filter (NSF) to polarize neutron beams. By reversing the spin states of the 3He 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 500ms we can spin flip a polarized 3He neutron spin filter with only 1.8×10−5 loss in 3He polarization. The small magnetic fields (10–15G) used to house neutron spin filters mean the 3He resonant frequencies are low enough to be generated using a computer with a digital I/O card. The versatility of this systems allows AFP to be performed on any beamline or in any laboratory using 3He neutron spin filters and polarization losses can be minimised by adjusting sweep parameters. ► Polarized 3He neutron spin filters are used to polarize neutron beams. ►Employs adiabatic fast passage to reverse 3He spin state of neutron spin filter. ► No need for an additional spin flipper. ► I/O card of 1.25 MS/s used to generate digital waveform. ► Small loss of only 1×10−53He polarization per flip obtained.