Status of the NIST Spin Filter Project

Abstract

Polarized ³He has long been recognized as a promising candidate for producing beams of polarized neutrons by selective absorption of one neutron spin state from an initially unpolarized beam. This technique has advantages over the traditional supermirror technique in that the neutron beams produced have less divergence added by the polarization technique (an advantage for SANS applications), lower backgrounds from gamma production (mainly important for fundamental physics research), and most importantly ³He can polarize thermal and epi-thermal neutrons as well as cold neutrons. We are pursuing parallel efforts at NIST to produce a practical spin filter either by polarizing ³He using spin-exchange with optically pumped alkali vapors or by direct optical pumping of metastable ³He followed by compression with a mechanical pump. The status and prospects of both of these projects are reported in this paper.