Record high counting rate of positron annihilation lifetime spectrometer achieved by β+-γ coincidence

Abstract

Conventional positron annihilation lifetime (PAL) spectrometers, which employ the $\gamma \text{-}\gamma$ coincidence with two perpendicularly-positioned detectors, have a typical counting rate of 100–300 counts per second (cps). To increase the counting rate, according to the optimized structural parameters using Geant4 simulation, a ²²Na positron source ($\sim$ 1.665 MBq), a silicon photomultiplier (SiPM), and digital waveform technology are utilized for the first time to a ${\beta }^{+}\text{-}\gamma$ coincidence PAL spectrometer. After the optimization and verification of accuracy and stability, this spectrometer can achieve a time resolution of about 206 ps, and a record high effective counting rate of approximately 19 000 cps ($\sim$ 11 000 cps/MBq), which is two orders of magnitude greater than those of conventional PAL spectrometers. The significant shortening of measurement time for a single PAL spectrum enables us to observe sub-minute-scale evolution of microstructure during rapid physical and chemical processes in the future.