Optimization of scintillation-detector timing systems using Monte Carlo analysis

Monte Carlo analysis is used to model statistical noise associated with scintillation-detector photoelectron emissions and photomultiplier tube operation. The impulse response of a photomultiplier tube, front-end amplifier, and constant-fraction discriminator (CFD) is modeled so that the effects of front-end bandwidth and constant-fraction delay and fraction can be evaluated for timing-system optimizations. Monte Carlo timing resolution for a bismuth germanate (BGO)/photomultiplier scintillation detector, CFD timing system is presented as a function of constant-fraction delay for 511-keV coincident gamma rays in the presence of Compton scatter. Monte Carlo results are in good agreement with measured results, indicating better timing resolution with decreasing constant-fraction delay. Monte Carlo energy-discrimination performance is experimentally verified along with the timing resolution (Monte Carlo resolution of 3.1 ns FWHM versus measured resolution of 3.3 ns FWHM) for a front-end rise time of 10 ns (10-90%). CFD delay of 8 ns, and CFD fraction of 20%.<>