  Incoherent background can create an intrinsic problem for standard small
angle neutron scattering measurements. Biological samples contain hydrogen
which is a strong incoherent scatterer thus creating an intrinsic source of
background that makes determination of the coherent scattering parameters
difficult in special situations. This can especially be true for the Q-range
from around 0.1-0.5 \AA^-1 where improper knowledge of the background level can
lead to ambiguity in determination of the samples structure parameters.
Polarization analysis is a way of removing this ambiguity by allowing one to
distinguish the coherent from incoherent scattering, even when the coherent
scattering is only a small fraction of the total scattered intensity. ^3He spin
filters are ideal for accomplishing this task because they permit the analysis
of large area and large divergence scattered neutron beams without adding to
detector background or changing the prorogation of the scattered neutron beam.
This rapid note describes the application of ^3He neutron spin filters,
polarized using the spin-exchange optical pumping method, for polarization
analysis on a protein sample to unambiguously extract the coherent scattered
intensity.
