The polarized neutron small-angle scattering instrument at BENSC Berlin

A polarized neutron beam has been installed at the small-angle neutron-scattering instrument V4 at BENSC Berlin. The main component of this new option is a 1.8 m long cavity transmission polarizer. The advantages of this device compared to the conventional bender polarizers are: (i) high transmission (35% of unpolarized beam at j" 6A s ); (ii) the polarization is better than 93% in the wavelength band 4 As (j(10 As and drops slightly to 80% at j"18 As ; (iii) the neutron beam is not de#ected. Thus, the polarized beam can be switched on and o! by rotating the polarizer or a conventional neutron guide into the beam without any readjustment of the beam path downstream the polarizer. An adiabatic radio frequency gradient spin #ipper in front of the sample provides high #ipping e$ciency over the whole wavelength band. First results on a sample with weak magnetic scattering (nanosized Fe 3 O 4 particles embedded in a glass matrix) are presented and compared to a measurement with unpolarized neutrons. ( 2000 Elsevier Science B.V. All rights reserved.