Application of large-area avalanche photodiodes to energy-dispersive x-rayfluorescence analysis

The performance of several large-area avalanche photodiodes (LAAPDs) for ap plication to x-ray spectrometry at room temperature was investigated. Optim um detector performance was obtained for gains of about 50-70. Good energy linearity of the LAAPDs' response to x-rays was observed up to energies of about 25 keV. For this energy range the space charge effects are negligible for gains below 100-150. The energy resolutions obtained with LAAPDs can b e better than those obtained with proportional counters. Our results indica te that the energy resolution of an LAAPD is better than that of a proporti onal counter only when the LAAPD maximum dark current is < 300 nA. For this case, minimum detectable x-ray energies of about 1 keV are possible. Spati al non-uniformity is responsible for an absolute increase of 1-2% in energy resolution at 6 keV when illumination of the LAAPD is broadened from 1 mm diameter to full area. Counting rates up to 5 X 10(4) counts s(-1) are poss ible without significant degradation of detector performance. Copyright (C) 2001 John Wiley & Sons, Ltd.