Subnanosecond timing with large area avalanche photodiodes and LSO scintillator

The detection properties of 10 mm and 16 mm diameter bevelled-edge avalanche photodiodes fitted with LSO crystal were measured using ψ-sources. Among the properties measured were the electron-hole pair yield, time resolution and energy resolution. These detectors provide excellent time resolution of 570±17 ps for ⁶⁰Co γ-rays with the energy threshold set at 1 MeV. The energy resolution of the 662 keV γ-peak from a ¹³⁷Cs source was measured to be 11% FWHM with a shaping time constant of 0.1 μs. A comparative discussion of the observed time resolution of these large area APDs emphasizes that APD gain, its quantum efficiency, and capacitance are important in timing applications