Calibration of spiral-readout image-plate detectors

An improved method for intensity-uniformity calibration of diffraction data collected on spiral-readout image-plate (IP) systems is described. This technique is applicable to all types of spiral-readout IP detectors. The procedure utilizes an attenuated direct-beam scan of the IP to generate a radial-sensitivity calibration table. Exposure and scanning of the calibration frame are done on the same time scale as typical data collections, and require no additional equipment. Speci®c examples are presented for use with Mac Science DIP2000 systems. The new radial calibration is shown to reduce signi®cantly structure-based R factors. The improved radial calibration is also shown to lower Rmerge when the IP is offset from the beam center. In addition to improving data quality and statistics, this method provides a quick and simple diagnostic tool to monitor changes in the sensitivity of the IP detector as a function of age.