Quantum efficiency measurement of an x-ray charge-coupled device by means of an x-ray generator monochromatized over the 0.2-1.2 keV spectral region.

Abstract

The Atomic Energy Commission has been developing an x-ray calibration laboratory for several years close to the Laser MégaJoule Facility mainly to calibrate x-ray cameras. Based on x-ray generators, great effort is being carried out to obtain x-ray monochromatic sources over the 0.1-10 keV spectral range. Moreover, their routine availability is a prerequisite while getting reduced uncertainties. To achieve this purpose, two x-ray monochromators have been recently developed, the former running below 1.5 keV and the latter in the harder x-ray region. The work presented in this paper constitutes, to the best of our knowledge, the first radiometric calibration of an x-ray camera, namely, a charge-coupled device (CCD). The CCD is thin and back illuminated with a 1300×1340 pixel, 20 μm×20 μm area. It has been calibrated by means of our soft x-ray monochromator based on Rowland circle geometry. This apparatus is able to take on board simultaneously two detectors under vacuum: the CCD to be calibrated and a silicon drift spectrometer (SDD), which acts as a reference detector to obtain the x-ray monochromatic intensity. An internal specific vacuum manipulator allows putting successively each detector in front of the scanning exit slit. Quantum efficiency (QE) of the CCD has thus been measured over the 0.2-1.2 keV region, due to the reference SDD. The latter was previously calibrated on the same monochromator by cross-calibration with another SDD calibrated at the Physikalisch-Technische Bundesanstalt (PTB) Radiometry Laboratory, on the synchrotron radiation facility BESSY. QE measurements are then compared to the CCD manufacturer's model and with previous ones performed on the same camera by means of our hard x-ray monochromator (2-10 keV). Comparison of these results with further PTB efficiency calibration of the reference SDD used to calibrate the CCD is discussed and allows concluding definitively about the validity of measurements performed by our x-ray monochromators.