The ORNL 10-meter small angle X-ray scattering camera

A new small-angle X-ray scattering camera which utilizes a rotating-anode X-ray source, crystal monochromatization of the incident beam, pinhole collimation, and a two-dimensional position-sensitive proportional counter has been developed. Because the sizes of the X-ray focal spot, the sample and the resolution element of the detector are each approximately 1 × 1 mm, the camera was designed so that the focal spot-to-sample and sample-to-detector distances may each be varied in 0.5 m increments up to 5 m to provide a system resolution in the range 0.5 to 4.0 mrad. A large, general-purpose specimen chamber has been provided into which a wide variety of special-purpose specimen holders can be mounted. The detector has an active area of 200 × 200 mm and has up to 200 × 200 resolution elements. The data are recorded in the memory of a minicomputer by a high-speed interface which uses a microprocessor to map the position of an incident photon into an absolute minicomputer memory address. With this interface, over 10⁵ events s^-1 can be recorded. The data recorded in the computer memory can be processed on-line by a variety of programs designed to enhance the user's interaction with the experiment. Among these are routines for background and detector-sensitivity correction, contour and perspective plotting of the two-dimensional data, a variety of averaging schemes for determining circular averages and/or one-dimensional slices of the data, file-management programs to handle the large quantity of data produced by a two-dimensional detector, and an interactive package for communications with a central computing facility via a dedicated hardwired link. At the highest angular resolution (0.4 mrad) the flux incident on the specimen is 1.0 × 10⁶ photons s^-1 with the X-ray source operating at 45 kV and 100 mA. The performance of the instrument is demonstrated with several examples, among which are scattering patterns from voids in neutron-irradiated nickel, plastically deformed polyethylene and collagen fibrils. Results from a kinetic study of the crystallization of polyethylene are also reported.