A feasibility study of ortho-positronium decays measurement with the J-PET scanner based on plastic scintillators

TL;DR

This study explores the use of the J-PET scanner, based on plastic scintillators, for detecting gamma rays from ortho-positronium decays, demonstrating its potential for high-resolution measurements and symmetry tests beyond medical imaging.

Contribution

The paper introduces the feasibility of using the J-PET scanner for o-Ps decay studies, highlighting its high angular and energy resolution capabilities with plastic scintillators.

Findings

J-PET can measure o-Ps decay with ~0.4° angular resolution.

Energy resolution achieved is approximately 4.1 keV.

Plastic scintillators offer faster signals, reducing background and pileup.

Abstract

We present a study of the application of the Jagiellonian Positron Emission Tomograph (J-PET) for the registration of gamma quanta from decays of ortho-positronium (o-Ps). The J-PET is the first positron emission tomography scanner based on organic scintillators in contrast to all current PET scanners based on inorganic crystals. Monte Carlo simulations show that the J-PET as an axially symmetric and high acceptance scanner can be used as a multi-purpose detector well suited to pursue research including e.g. tests of discrete symmetries in decays of ortho-positronium in addition to the medical imaging. The gamma quanta originating from o-Ps decay interact in the plastic scintillators predominantly via the Compton effect, making the direct measurement of their energy impossible. Nevertheless, it is shown in this paper that the J-PET scanner will enable studies of the o-Ps$\to3\gamma$ decays with angular and energy resolution equal to $\sigma(\theta) \approx 0.4^{\circ}$ and $\sigma(E) \approx 4.1$ keV, respectively. An order of magnitude shorter decay time of signals from plastic scintillators with respect to the inorganic crystals results not only in better timing properties crucial for the reduction of physical and instrumental background, but also suppresses significantly the pileups, thus enabling compensation of the lower efficiency of the plastic scintillators by performing measurements with higher positron source activities.