A new detector for time-resolved small angle X-ray scattering studies

A new detector for time-resolved small-angle X-ray scattering has been designed and built for experiments at the Advanced Photon Source of Argonne National Laboratory. This detector is made from a 500 /spl mu/m thick by 150 mm diameter ultra-high purity silicon wafer, which directly converts X-rays into electron-hole pairs. The electrodes are concentric rings that integrate the scattered X-rays over the azimuthal angle. The widths of the rings are optimized for the size of the X-ray beam and its energy spread. Only 128 rings, or channels, are needed to measure a scattering profile. The read-out electronics consist of preamplifiers with pulse-shaping, which are mounted on the detector, and 12-bit, 20 MHz digitizers. The resolving time of the electronics is 300 ns, which is sufficient to isolate a single pulse of scattered X-rays when the synchrotron is operated with a hybrid or asymmetric fill pattern. The data acquisition hardware can average a programmable number of digital samples, up to 64, every 3.68 /spl mu/s (the period of the synchrotron) to provides a single 12-bit average of the voltage from the analog amplifier chain. The temporal range of the detector is 3.68 seconds or longer and may be controlled by the experimenter. An alpha source is used to calibrate the detector and electronics, and document their performance. Preliminary results obtained during the commissioning of the detector are presented.