Measurements of Fano factors in silicon and germanium in the low-energy X-ray region

Estimates of Fano factors have been made in the low-energy X-ray region for both silicon and germanium (109 eV to 5.9 keV for silicon and 183 eV to 5.9 keV for germanium). The measurements are based on observations on a large number of X-ray detectors taking into account the effects of incomplete charge collection. The values at an X-ray energy of 5.9 keV are 0.1161 ± 0.0001 and 0.1057 ± 0.0002, respectively, for silicon and germanium at cryogenic temperatures. The values are found to converge and increase to about 0.15 at 183 eV. Comparisons are made with theoretical predictions and the difficulties of making measurements in the 100 eV region are discussed.