Polarization analysis with

Polarization analysis with

He spin filters to separate coherent scattering from total scattering in SANS

E. Babcock, Z. Salhi, M-S. Appavou, A. Feoktystov, V. Pipich, A.

Radulescu, V. Ossovyi, S. Staringer, A. Ioffe

E-Mail: e.babcock@fz-juelich.de

In soft matter SANS studies, especially at large Q, incoherent scattering becomes the dominant signal. The incoherent contribution can be orders of magnitude larger than the coherent signal of interest; even after the total signal from the solvent is subtracted. This is an intrinsic problem because this remaining incoherent signal comes from the sample itself and would obscure the desired structural information when the coherent scattering level drops far below the incoherent.

Polarization analysis has the potential to fully separate the coherent signal from the incoherent signal and make analysis of difficult samples more certain or even possible at all: one can increase the fidelity of the coherent signal such that weak scattering can still be seen clearly.

However, because of inelastic scattering one must be very careful to correctly perform the polarization and detector efficiency corrections if the scattering is desired in absolute units in the large Q-range, where the coherent scattering is one or more orders of magnitude lower than the sample’s incoherent scattering. Therefore, we have performed time-of-flight measurements on the SANS diffractometer KWS2 of the JCNS in Garching to look at the amount of inelastic scattering in order to perform this correction accurately.

This presentation will address the issues associated with the correct separation of coherent and incoherent scattering for soft matter samples and propose and describe a method of implementation using ³He spin filters and future plans at the JCNS. As a demonstration the results of tests measurements on KWS2 will be presented: they show the viability of the method on a protonated α-lactalbumin solution at 2.5% and 0.25% concentrations in a D2O buffer solution.