The influence of average photon number on the measured fluorescence decay time of scintillator

Measurement of the light decay time by the delayed single-photon coincidence method requires that the average number of photons detected by photomultiplier tube be much less than one. The probability that multiple photons will be detected during the measurement always exists and makes the measured time decay spectrum appear to be faster than the true one. By using the probability density function of detected fluorescence photon, Monte-Carlo simulations and numerical calculation, the quantitative relationship between the deviation of measured fluorescence decay time and the average photon number is obtained. It is found that the deviation is directly proportional to the average photon number and inversely proportional to the time range of TAC. The methods to determine the average photon number are discussed.