A Novel Technique for Accurate Intensity Calibration of Area X-ray Detectors at Almost Arbitrary Energy

Abstract

A novel intensity uniformity calibration method for area X-ray detectors is described. In diffraction experiments, amorphous lithium glass plates, containing doping elements chosen for their K edges just below the energy of the main beam, replace the crystallographic samples for the calibration measurement. The fluorescent emission excited by the X-ray beam is almost isotropic. It has exactly the same geometry as the diffracted radiation, and can be obtained at the same wavelength by proper selection of the element and excitation energy. A sample 2theta scan allows the emission distribution as a function of angle to be characterized with an accuracy of a fraction of a percent. This allows a flat-field correction of similar accuracy. The quality of crystallographic data collected with an X-ray image intensifier/CCD detector was significantly improved by flat-field correction using an Sr-doped lithium tetraborate glass. This technique can be applied to X-ray energies from 5 to 50 KeV; the calibration sample is small, stable and easily handled.

Expression, crystallization, and preliminary X-ray analysis of a sialic acid-binding fragment of sialoadhesin in the presence and absence of ligand

“…Cocrystals: Initial data were collected from a single cocrystal flash frozen using an Oxford Cryosystems Cryostream on beam line BL19 (Thompson et al, 1996) at the ESRF, Grenoble. Crystals were soaked in a cryoprotectant solution containing 15% MPD (v/v) 30% PEG4000 (w/v), 0.1 M sodium citrate, pH 5.6, 0.2 M ammonium acetate, 25 mM 2,3 sialyllactose prior to freezing in the dry air stream at 104 K; 0,979-A wavelength synchrotron radiation was used and data recorded using a CCD-based detector (Moy, 1994).…”

“…Crystals were soaked in a cryoprotectant solution containing 15% MPD (v/v) 30% PEG4000 (w/v), 0.1 M sodium citrate, pH 5.6, 0.2 M ammonium acetate, 25 mM 2,3 sialyllactose prior to freezing in the dry air stream at 104 K; 0,979-A wavelength synchrotron radiation was used and data recorded using a CCD-based detector (Moy, 1994). X-ray data were collected by the oscillation method using 1" oscillations, calibrated, and corrected for spatial distortion (Hammersley et al, 1995;Moy et al, 1996). High-resolution data to a maximum resolution of 1.85 A were collected using 1 .O-A wavelength synchrotron radiation (0.1 -mm collimation) at 14 "C on beam line BL6A2 (Sakabe, 1991) of the Photon Factory, Tskuba, Japan.…”

Rapid methods for the calibration of solid-state detectors

“…It is based upon a method recently developed for calibrating area X-ray detectors (Moy et al, 1996). A glass containing selected elements is held in a polychromatic beam of X-rays and the¯uorescence lines from the selected elements are used for the energy calibration.…”

Calibration and Application of an X-ray Image Intensifier/ Charge-Coupled Device Detector for Monochromatic Macromolecular Crystallography

“…We do not know of a perfect isotropic point source at arbitrary X-ray energies. However, we have found that very smooth 'floodfield'-~ emission may be obtained at a wide variety of X-ray energies by using the fluorescence from doped dilithium tetraborate glasses (Moy et al, 1996). These glasses are relatively easy to manufacture from raw materials provided that a few basic preparation rules are followed (Foust, 1995).…”