Physica B 356 (2005) 96–102 Polarized 3 He spin filters in neutron scattering T.R. Gentile a,Ã , E. Babcock b , J.A. Borchers a , W.C. Chen a,c , D. Hussey c , G.L. Jones d , W.T. Lee e , C.F. Majkzrak a , K.V. O’Donovan a,f , W.M. Snow c , X. Tong c , S.G.E. te Velthuis g , T.G. Walker b , H. Yan c a National Institute of Standards and Technology, 100 Bureau Dr, MS 8461, Gaithersburg, MD 20899, USA b University of Wisconsin-Madison, Madison, WI, USA c Indiana University, Bloomington, IN 47408, USA d Hamilton College, Clinton, NY 13323, USA e Spallation Neutron Source, Oak Ridge, TN, USA f University of Maryland at College Park, College Park, MD, USA g Argonne National Laboratory, Argonne, IL, USA Abstract We report progress in the development and application of neutron spin filters based on transmission through polarized 3 He gas. Tests and application of these devices are underway at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) and the Intense Pulsed Neutron Source (IPNS). The results of application to polarization analysis for diffuse reflectometry is discussed, along with an example of the issues in choosing the flipping ratio for such applications. The status of our development of polarized gas production using both spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping will be presented. For SEOP, we currently obtain 70–75% 3 He polarization in cells up to 500cm 3 in volume. r 2004 Elsevier B.V. All rights reserved. PACS: 83.85.Hf Keywords: Helium; Neutron; Optical pumping; Polarization; Spin filter 1. Introduction Polarized 3 He spin filters are under development for neutron scattering at several neutron facilities inEurope [1].Inthispaper,wereviewthestatusof a collaborative program in the US that includes contributions from the National Institute of Standards and Technology (NIST), Indiana Uni- versity, Hamilton College, the University of Wisconsin, Argonne National Laboratory, and the Spallation Neutron Source. We are currently ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.10.056 Ã Corresponding author. E-mail address: thomas.gentile@nist.gov (T.R. Gentile).