Si(Li) Detector Efficiency and Peak Shape Calibration in the Low-Energy Range Using Synchrotron Radiation

Abstract

The efficiency and pulse distribution characterization of an Si(Li) detector (SLD) were obtained using the mono-chromatized Super-ACO (LURE, Orsay, France) synchrotron beam. The selected energies ranged from 700 to 7000 eV and the radiation intensity was successively measured with a proportional counter, used as a reference, then with the detector to be calibrated. More than 100 experimental points were recorded; steps as small as 1 eV were used to examine carefully the silicon and gold absorption edges. The SLD spectra were processed using the COLEGRAM deconvolution software, which fits different theoretical functions to experimental data. The processing includes a least-squares fitting with the Marquart–Levenberg algorithm and the use of a Hypermet-type function, the sum of a main Gaussian function with a low-energy tail. The proportional counter efficiency curve is calculated using attenuation coefficients for the polypropylene window and argon–methane counter gas. The complete SLD peak shape calibration was obtained: the variation of each fitting function parameter with energy is shown. The tailing parameters show sharp discontinuities that can be linked to different interaction points in the detector front end. This detector pulse distribution calibration obtained with monochromatized radiation could be used to process accurately usual X-ray spectra including several peaks and satellites. The uncertainty in the SLD efficiency calibration points is about 3%. The experimental values were fitted with a theoretical function describing the transmission through different absorbing layers. It is seen that the so-called silicon ‘dead layer’ acts as a partially active layer, the corresponding events being recorded in the peak tail. © 1997 John Wiley & Sons, Ltd.