Figure 1

Detector module circuit. Each detector module houses a number of APDs (up to six), all of which were irradiated to a common fluence. The circuit diagram for a single detector channel is shown - each APD is embedded in passive avalanche quenching electronics with an external high-voltage supply and output to a time-tagging unit (the time-tagging unit has a fixed-threshold discriminator at each input) or to an oscilloscope.