THE POLARIZING BEAM SPLITTER GUIDE AT BENSC

A polarizing beam-splitter guide, theoretically described earlier, was installed in the neutron guide hall at BENSC in the winter of 1993/94. It splits the incoming neutron beam with wavelengths beyond 2.5 Angstrom into two oppositely polarized beams. The active elements of the splitter system are Si-CoFe supermirrors deposited on Si wafers, which show a good polarization capability between the critical angle of Si of 0.047 degrees per Angstrom neutron wavelength and a cut-off angle of 0.21 degrees per Angstrom, i.e. twice the critical angle of natural Ni. For single mirrors in the supermirror region an average reflection coefficient of 90% was achieved at a polarization of 96% for the reflected beam while the transmission coefficient amounted to 80% for a polarization of 97%. These values apply for a magnetizing field of 300 G and improve slightly for higher fields. Preliminary results for the whole guide show a polarization above 92% for neutrons with a wavelength of 3 Angstrom.