Calibration of CCD detector after damage
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Calibration of CCD Detector after Damage A. P. Dudka Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia e-mail: [email protected] Received April 9, 2015
Abstract—An Xcalibur X-ray diffractometer with a Sapphire 3 CCD detector (Rigaku Oxford Diffraction) has been calibrated to remove damage effects. Visual proof of the validity of the detector calibration map is obtained for the first time. The calibration has significantly improved the reliability of the structural data on Ba3TaFe3Si2O14 single crystal. DOI: 10.1134/S1063774515060073
The total-intensity recording anisotropy of modern diffractometers with area detectors significantly exceeds that of diffractometers with point detectors. The standard diffractometer software cannot completely eliminate the corresponding distortions. The procedure for calibrating CCD detectors that was proposed in [1, 2] and implemented in the ASTRA software [3] implies calculation of two correcting factors for each reflection: in the dependence of the reflection coordinates in the detector plane and in the dependence on the goniometer setting angles. In addition, the introduction of an additional “relationship” between the low- and high-angle reflections provides a smaller distortion of atomic displacement parameters in refinement of the model. The use of calibration [1, 2] made it possible to obtain a number of reliable structural results [4, 5].
although their accuracy was expected to be comparable with the accuracy for similar samples analyzed before the damage. To improve the situation, we performed two experiments with a Ba3TaFe3Si2O14 single crystal (langasite family), differing by the rotation of ellipsoidal sample by 90° around the goniometric head axis. The detector area was divided into 16 × 16 squares, and a correction factor was calculated for each square. Calculations [2] reproduced the observed anomaly in the detector calibration map (Fig. 2). It turned out that, after the damage, the detector response within the spot (observed in the top part) was lower than the response
In January 2015, several damages occurred on an Xcalibur diffractometer with a Sapphire 3 CCD detector (Rigaku Oxford Diffraction), including the breakage of two glass X-ray tubes with water leakage. When the working possibility of the diffractometer was recovered, the diffraction patterns (frames) of all measured crystals were found to contain an anomaly: a spot in the top part (Fig. 1). A verification showed that the pressure in the detector is even lower than that recommended by manufacturer; therefore, the nature of the anomaly is unclear. The routine maintenance aimed at recovering the necessary vacuum level in the detector and implementing the slow heating/cooling mode did not lead to success. The detector response distortions, which were previously revealed by calculation [2] but could not be seen directly in frames, became so large that could be visualized for the first time. The standard software (CrysAlis [6]
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