Recent advances in polarised 3He spin filters at the ILL

Abstract

We report the present status and recent advances made in polarised- 3He spin-filters at the ILL. The Tyrex filling station is working reliably and producing polarised 3He 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 3He spin filters for reflectometry are presented and compared to the presently used supermirror-based polarisation analysers. By increasing the optical thickness of 3He 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 an experiment. We present the performance of a 3He spin flipper, which inverts the polarisation direction of the 3He 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 3He spin filters to be used in inaccessible regions, such as inside large-detector vacuum tanks and in high-radiation environments.