LEAST-SQUARES ARRIVAL TIME ESTIMATORS FOR SINGLE AND PILED UP SCINTILLATION PULSES

The ability to accurately determine the detection time of gamma rays h as important applications in nuclear science. For gamma ray imaging sy stems, improvements in detector timing resolution can substantially re duce the signal to noise ratio of the images. This paper will develop a new arrival time estimator for the detection of gamma rays using sci ntillation detectors. The estimator structure reduces to a weighted le ast squares (WLS) estimate of the arrival time and has been found to b e the optimal estimator for scintillation pulses. This WLS estimator w as applied to scintillation type pam with fast rise times and exponent ial decays. The timing resolution was calculated and compared to the r esolution of leading edge and constant fraction triggers for a Burle 8 850 photomultiplier tube, and to the Cramer-Rao lower bound on estimat or performance. The WLS estimator has out performed these conventional arrival time estimators and has the added ability of simultaneously e stimating the arrival times of multiple overlapping pulses. This allow s for piled up pulses to be effectively separated permitting their ind ividual energies to be estimated.