Recent advances in polarised 3He spin filters at the ILL

We report the present status and recent advances made in polarised-He-3 spin-filters at the ILL. The Tyrex filling station is working reliably and producing polarised He-3 for neutron spin filters on a daily basis. The latest spin-filter cells have wall relaxation times between 200 and 400 h-the longest relaxation times yet achieved for valve-sealed cells. Recent results using He-3 spin filters for reflectometry are presented and compared to the presently used supermirror-based polarisation analysers. By increasing the optical thickness of He-3 gas, we move into a regime in which the neutron beam polarisation decays with a time constant of the order of a thousand hours and is thus negligible within the 24 h time scale of ail experiment. We present the performance of a He-3 spin flipper, which inverts the polarisation direction of the He-3 nuclei by adiabatic fast passage with a polarisation loss of 10(-5) per flip. The development of in situ filling of the spin-filter cell via a capillary is described. This "local filling" technique enables He-3 spin filters to be used in inaccessible regions, such as inside large-detector vacuum tanks and in high-radiation environments. (c) 2006 Elsevier B.V. All rights reserved.