3He neutron spin-filter

Neutron spin-filters (NSF) using gaseous polarized He-3 offer the possibility to polarize neutrons over the full spectrum of cold, thermal and hot neutrons. This report gives an account of the present status of the NSF development programme at ILL. The polarization technique is based on direct optical pumping of metastable He-3 atoms in a low pressure discharge cell with a subsequent polarization-preserving mechanical compression of the gas up to several atmospheres, necessary to run a NSF. The concept of a remote type of operation using detachable NSF cells is presented which requires long nuclear spin relaxation times of order 100 h. A first survey of their use under experimental conditions is given. (C) 1999 Elsevier Science B.V. All rights reserved.