A method to increase scintillation lifetime measurement rates using a multi-hit TDC

Summary form only. A method for using a modern TDC (time-to-digital converter) to increase the scintillation lifetime measurement rate by a factor of over 300 is discussed. It uses the delayed coincidence method, where a start photomultiplier tube (PMT) provides a signal synchronized to the excitation of the specimen and a stop PMT samples the resulting fluorescent lifetime spectrum. Typical data acquisition rates are low because the light collection efficiency of the stop PMT is artificially limited to ∈≈0.001 fluorescent photons per start signal to reduce the probability of detecting >1 photon per excitation. Some modern TDCs can detect whether additional stop signals occur during the sampling period and thus reject events in which >1 stop photons are present. This allows ∈ to be increased to 1, which maximizes the data acquisition rate at a value over 300 times higher. Multi-hit TDCs can digitize the arrival times of n stop signals per start signal, which allows ∈ to be increased to ≈n. Since multiple photon events, which usually bias the data, are eliminated or measured, this method also improves the measurement accuracy