The working principle of metascintillators is based on sharing the energy of an impinging gamma ray between their composing materials. Such can be a dense crystal such as LYSO or BGO to maximize the gamma stopping potential and a fast organic or inorganic compound such as BC-422, EJ232 or BaF2 for its light production kinetics. In this work we look into the details of metascintillator pulses as modelled through a double bi-exponential model. We analyze the extent of energy sharing, as understood through analysis, simulation and experiment in a coincidence timing resolution (CTR) measurement setup, using 3x3x15 mm3 metascintillators, against a reference detector. Features of individual pulses allow choosing the photoelectric interactions and provide insight on the energy sharing extent of each gamma interaction. We evaluate the quality of energy sharing surrogates for different metascintillator designs. Different populations of photoelectric interactions depending on the extent of energy sharing are defined, that have different contribution of fast photons in the first picoseconds and hence different timing. We benchmark this selection through using these features to apply a timewalk correction on an event-to-event basis. A significant improvement is demonstrated in all cases, while for a 3:1 volume ratio BGO:EJ232 metascintillator this improvement rises up to ~25% for the whole photopeak (204.7 ps), while the 10% events with higher production in the fast emitter show a ~50% improvement to 54.7 ps. This shows that while metascintillators with comparable light yield components still provide the best alternative, it is possible through simple pulse analysis to measure and isolate the photoelectric interactions in every metascintillator with two components

Riccardo Latella

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