PHOTOELECTRON ESCAPE FROM A SILICON X-RAY-DETECTOR - MONTE-CARLO STUDY

Photoelectron escape fractions for small X-ray detectors used in the measurement of diagnostic X-ray spectra are calculated using a Monte Carlo method. The calculation is carried out for detectors 50 to 500 mu m in thickness and at several different diameters with incident photons in the energy range 10-300 keV. When a photoelectron escapes, the partial energy of an incident photon is absorbed in the detector; the spectra of the absorbed energy are shown. The calculated escape fractions are compared with experimental data, and a good agreement is obtained. The diagnostic X-ray spectra measured with a silicon detector 95 mu m in thickness is corrected for detector distortion using the calculated escape fraction; with this correction, a spectrum similar to that determined with a Ge detector is obtained. For an easy calculation of the escape fractions, an empirical equation is presented; this equation gives the escape fractions for any size of detector. The escape fraction depends strongly on detector size and on photon energy; the detector size suitable for measured X-ray energy is also discussed.