Use of energy summing for selection of coincidence events in positron-lifetime spectroscopy

A BaF2 positron-lifetime spectrometer equipped with a coincidence system that represents a compromise between the traditional fast-fast and fast-slow arrangements is described. The main difference of the present configuration from both the fast-slow and fast-fast ones consists in use of a sum of the energy signals from the start and stop detectors to select the coincidence events. Quality of the spectrometer response function (approximate to 150 ps FWHM for Na-22) is very close to that observed for our fast-slow configuration with the equivalent detectors but throughput, of the present apparatus is increased almost by a factor of two. Moreover, the electronic scheme becomes less complicated, which has also a positive impact on its cost.