The asset of ultra-fast digitizers for positron-lifetime spectroscopy

A spectrometer for positron-lifetime measurements assembled from two BaF2 scintillation detectors and two 8-bit, 4GSs-1 digitizes in a master-slave configuration is described in detail. We report the results of comparative testing measurements of the lifetime of positrons annihilating in α-Fe using this setup and a setup formed by the same pair of detectors working in conjunction with analog electronics modules. The data from these measurements demonstrate for the first time that replacing the analog electronics chain by fast digitizers leads to a substantial improvement of the precision in positron-lifetime measurements. A record timing resolution of 131-136 ps has been achieved with the described spectrometer at coincidence counting rate comparable or virtually equal to that obtained with the fast-fast setup.