Small Angle Resolution of a SAXS Camera

The discussion will be limited to the case of the focusing, pinhole SAXS-camera. The advantages of this type of camera are an optimized flux at the sample and the absence of slit smearing effects encountered in Kratky-cameras [12]. 

The largest observable d-spacing of such a camera depends on the limits of diffuse scattering in the detector plane. This limit — L — can be approximately calculated from the size of the aperture slits (St), the distance of the detector plane from the guard slits (Lj) and the size of the focus (a) [4], In real space one can write  

For the following discussion a coordinate system based on the source point will be used. (Fig. 3 a) s is tangent to the electron beam at the source point. The electron (or positron) trajectory is in the x — s plane. P is an observation point defined by the angles 0 and q . The magnetic field vector is along z. 

The size of the aperture slits in the horizontal (S ) and vertical (S ) directions is calculated from the photon beam source point size — x, z (ct) —, divergence — x, z (a) and F1 which is the distance source point to aperture slits  

The extent of the diffuse scattering in the detector plane is therefore dominated by the size of the aperture slits (S ) and the length of the camera after the optical elements (F2). 

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