SANS polarization analysis at V4 SANS instrument of HMI Berlin

The V4 instrument has recently been upgraded with a 3He spin filter cell, placed directly in the homogeneous field B of the sample magnet, to enhance the SANSPOL option for polarization analysis. The prototype setup was still affected by: (a) a quick relaxation of the 3He nuclear polarization in the cell with a time constant of only ?130 min which significantly changes the spin filter transmissions T+ and T? for neutrons polarized parallel I+ and anti-parallel I? to B, and (b) the absence of a flipping aid behind the sample. The usual polarization analysis procedure, expecting virtually time-independent transmissions and a second flipping device, is therefore not applicable. We present an a…