Construction and testing of a multichannel polariser for thermal neutrons

A curved polarising multichannel neutron guide with total beam cross section 26 × 56 mm2, containing 20 channels was produced at PNPI. The concave sides have a supermirror coating consisting of the alloys Co64Fe34V2 and Ti60Zr40, giving θcλ = 34(±0.8) mrad/nm. The convex side is a natural Ni layer with θcλ = 17.5 mrad/nm. Both sides have an antireflecting underlayer based on an alloy of TiZr and Gd. All coatings were produced by sputtering. The characteristic bending angle for which the system is designed is 5.79 mrad giving a characteristic wavelength equal to 0.17 (±0.05) nm. The transmission and polarisation as functions of λ were measured at IRI by means of “Lannor precession spectroscopy” and the “3 polariser 2 shim method”, respectively. The transmission is equal to the theoretical value within 10%; the polarisation is 0.98 at λ = 0.16 nm decreasing to 0.75 at λ = 1.0 nm.