Large solid-angle polarisation analysis at thermal neutron wavelengths using a 3He spin filter

Abstract The strongly spin-dependent absorption of neutrons in nuclear spin-polarised 3 He opens up the possibility of polarising neutrons from reactors and spallation sources over the full kinematical range of cold, thermal and hot neutrons. In this paper we describe the first large solid-angle polarisation analysis measurement using a 3 He neutron spin filter at thermal neutron wavelengths ( λ =2.5 A). This experiment was performed on the two-axis diffractometer D1B at the Institut Laue-Langevin using a banana-shaped filter cell (530 cm 3 ) filled with 3 He gas with a polarisation of P =52% at a pressure of 2.7 bar. A comparison is made with a previous measurement on D7 using a cold neutr…