Behavior of a fast counting system with an avalanche photodiode detector for synchrotron X-rays

The behavior of a fast counting system with an avalanche photodiode (APD) detector was examined using X-rays produced by synchrotron radiation. The system with the APD detector had a dead time of about 4ns. This provided superior performance with a count-rate capability of up to 108 counts/s in a multi-bunch mode of a storage ring. The relation between the input photon rates and the observed count rates is given based on a model for pulsed X-rays. The model well explains the behavior of a system with the APD detector in a single-bunch mode and at input rates below 108 photons/s in a multi-bunch mode. However, at higher rates the shape and variable amplitude of the pulse from an amplifier cause a difference from the behavior predicted by the model.