Abstract
Abstract
Positron annihilation lifetime (PAL) spectroscopy is a
unique method for characterizing atomic-scale defects and
ultramicropores in materials. The conventional PAL spectrometer
adopts the γ-γ coincidence principle, and its
performance, especially the coincidence counting rate (CCR), can
hardly be further increased. Another coincidence principle,
β
+-γ coincidence, has the potential to
simultaneously improve the CCR and coincidence time resolution (CTR)
of PAL spectrometers. However, early β
+-γ
coincidence PAL spectrometers have not been widely applied due to
the considerable room for improvement in their performance. In this
work, we proposed a new β
+-γ coincidence PAL
spectrometer utilizing silicon photomultiplier (SiPM) array as the
positron detector and conducted a comprehensive optimization of its
structure with the aim of achieving a breakthrough in
performance. The effects of start signal threshold and structure
parameters on its CTR, CCR, and proportion of source contribution
(P
SC) were studied using Geant4. The simulation
results show that, with a 68Ge positron source of 30 μCi,
the optimized β
+-γ coincidence PAL spectrometer
can achieve an extremely high CCR exceeding 10000 counts per second
(cps) and an outstanding CTR below 160 picoseconds (ps) while
maintaining a low P
SC below 12%. This study
provides valuable guidance for constructing high-performance
β
+-γ coincidence PAL spectrometers.