CONSTRUCTION AND TESTING OF A MULTICHANNEL POLARIZER FOR THERMAL-NEUTRONS

A curved polarising multichannel neutron guide with total beam cross s ection 26 x 56 mm(2), containing 20 channels was produced at PNPI. The concave sides have a supermirror coating consisting of the alloys Co6 4Fe34V2 and Ti60Zr40, giving theta(c)/lambda = 34(+/-0.8) mrad/nm. The convex side is a natural Ni layer with theta(c)/lambda = 17.5 mrad/nm . Both sides have an antireflecting underlayer based on an alloy of Ti Zr and Gd. All coatings were produced by sputtering. The characteristi c bending angle for which the system is designed is 5.79 mrad giving a characteristic wavelength equal to 0.17 (+/-0.05) nm. The transmissio n and polarisation as functions of lambda were measured at IRI by mean s of ''Larmor precession spectroscopy'' and the ''3 polariser 2 shim m ethod'', respectively. The transmission is equal to the theoretical va lue within 10%; the polarisation is 0.98 at lambda = 0.16 nm decreasin g to 0.75 at lambda = 1.0 nm.