6533b86cfe1ef96bd12c8a3d

RESEARCH PRODUCT

SANS polarization analysis at V4 SANS instrument of HMI Berlin

subject

description

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 alternative way of polarization analysis, developed especially for this case of a spin filter cell with insufficient time stability, and not requiring a second flipper. A concentrated Co-ferrofluid sample 'MFT3N' was measured with the spin filter cell for 5.5 h. From the time-dependent change of I+ and I? caused by the change of T+ and T?, the spin-flip and non-spin-flip components of the scattering were calculated by fitting procedures. The two-dimensional flip patterns obtained represent the purely magnetic scattering contribution, featuring the typical (sin??cos??)2 angular behavior expected for superparamagnetic systems.