[en] We present a tool to investigate neutron depolarisation effects with 10⁻⁴ precision. The test bench consists of two opaque ³He cells with in-situ adiabatic fast passage flipping of the helium spin. The cells polarise a neutron beam to more than 99.99 % and analyse its polarisation with high accuracy. For depolarisation studies, a sample can be inserted between the two cells and its effect on a primarily highly polarised beam is analysed. The test bench has been validated at the cold neutron beam PF1B at Institut Laue-Langevin, France. We present here preliminary results for the wavelength range from 5Å to 7Å. Polarisation with super mirrors is limited to about 99.7%. Direct evidence of depolarisation in the order of 10⁻³ in polarising super mirrors was found by the test bench.

[en] We describe the development of a polarized neutron device that combines a ³He neutron spin filter and a neutron spin flipper using adiabatic fast passage (AFP), to adiabatically reverse the ³He polarization and thus the neutron polarization with near perfect symmetry. A typical AFP sequence takes place in 2.5-7.5 ms, with the time for the ³He transition from P to -P much less, thus the neutron polarization is nearly perfectly reversed very quickly with only a 2x10^-5 loss in ³He polarization per flip. We believe this device, the ³He 'flipperizer' can become a standard option wherever a ³He spin filter is already in use. Our first on beam test was performed on MIRA at the new FRM-2 reactor in Garching using polarized ³He from HELIOS. We also briefly describe tests of a new neutron flipper based on AFP. This broad band neutron RF flipper was shown to create neutron flipping efficiencies of >99% at a neutron wavelength of 0.4 A. Neutron tests were performed on D3 (ILL) and on ROTAX (ISIS)

[en] Polarized ³He has shown its unique characteristics in many areas of polarized neutron scattering, its ability to polarize neutrons at short wavelengths, accept wide-angle and divergent beams and low backgrounds enable new classes of experiments. While polarized ³He is not a steady state solution as commonly applied, the benefits have been shown to offset the drawbacks of polarizing and refreshing the polarization in the neutron spin filter cells. As an extension of this work, in-situ polarization using the spin-exchange optical pumping (SEOP) method was explored as a means to construct a system which could be used to polarize ³He in the state used for an effective neutron spin filter to constant polarization while on the neutron beam. An in-situ SEOP polarizer was constructed. This device utilized many devices and principles developed for neutron spin filters which are polarized off the beam line using either SEOP or metastability exchange optical pumping (MEOP) under the same research program. As a collimation of this work effects of extremely high neutron capture flux density >1x10¹⁰cm^-2s^-1 incident on the in-situ polarizer were explored.

[en] 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