Pulse-height measurements with a cooled avalanche-photodiode detector

A cooled avalanche-photodiode (APD) detector has been developed for X-ray diffraction experiments. Although an APD is normally used at room temperature and a high internal gain, the energy resolution can be improved by decreasing temperature and gain. The APD device was cooled to 253 K by a thermoelectric cooler. When the gain was M = 13, the energy resolution was 5% (FWHM) at 16.53 keV with a charge-sensitive preamplifier. By scanning the discriminator threshold level of a fast-counting system, energy spectra were obtained at M ≃ 50 and count rates of up to 4.7 × 10⁷ s⁻¹.