High-dynamic range SAXS data acquisition with an X-ray image intensifier

Data with a wide dynamic range of intensity can be collected with a pinhole high-brilliance small-angle X-ray scattering (SAXS) camera using an image-intensified charge-coupled device (CCD) detector. The point spread function (PSF) of this detector has a narrow peak with a broad low tail such that a high level of scattered intensity at small angles can cause a significant background in the detector elements at higher angles. A correction scheme for the long tail of the PSF of the detector is needed when this integrating area detector is used for measuring intensity that spans a dynamic range of four to five orders of magnitude. A procedure is described for measuring the PSF contribution by masking a small part of the detector from the scattered radiation with an absorbing material. In order to measure the PSF, it is necessary to use a high-intensity spot, which is readily achieved by using a sample that scatters strongly at small angles. Although this intensity is spread over many pixels, the sharp features in the scattering from the silica sample chosen for this study permit one to obtain simultaneously both the narrow and the broad parts of the PSF. The data are compared with the actual scattering function, which has been measured exactly with a point-geometry Bonse-Hart camera. The advantages of this procedure are discussed.