Digital strategies for time and energy measurement for ultra fast scintillators

Ultra fast inorganic scintillators, like LaBr
₃
(Ce) are key detectors in Nuclear Physics and medical applications. On the other hand, fully digital acquisition systems, for which the pulses from the detectors are sampled at high rates, are being increasingly used. We present new digital pulse processing algorithms to extract time and energy signals from nuclear pulses produced by ultrafast detectors. We compare the results of the fully digital acquisition chain (DDAQ) to state-of-the-art results obtained with traditional electronics, based upon constant fraction discriminators (CFD), time to digital converters and multichannel analyzers. For this purpose, we have performed coincidence measurements using relatively large (1"×1.5"×1”) truncated cone and cylindrical LaBr
₃
(Ce) and CeBr
₃
crystals coupled to ultra fast photomultipliers (PMTs). Coincidence measurements with Co-60 and Na-22 sources are acquired. The main advantage of fully digital processing is that many different algorithms may be applied to the same raw data set. Pulses from PMTs optimized for timing measurements were digitized to a switched capacitor array with a speed sampling of 5 Gs/s and a resolution of 16 bits, and to a fast digital oscilloscope able of 4 Gs/s and 8 bits resolution. With an in silico version of the analog CFD we obtain coincidence resolving times below 150 ps for Co-60, outperforming the standard acquisition system.