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 λ=6 Å); (ii) the polarization is better than 93% in the wavelength band 4 Å<λ<10 Å and drops slightly to 80% at λ=18 Å; (iii) the neutron beam is not deflected. Thus, the polarized beam can be switched on and off 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 flipper in front of the sample provides high flipping efficiency over the whole wavelength band. First results on a sample with weak magnetic scattering (nanosized Fe3O4 particles embedded in a glass matrix) are presented and compared to a measurement with unpolarized neutrons.