Fig. 8From: Estimating relationship between the time over threshold and energy loss by photons in plastic scintillators used in the J-PET scannerThree different cases in the events selection for the 1275 keV photons (orange arrows) based on the delayed decay of ortho-positronium atoms: a The first case shows the two annihilation photons (black arrows) from the decay of para-positronium (or ortho-positronium pick-off). b The photons originating from the decay of ortho-positronium state (three black arrows). c A possible source of background in the adopted procedure for the selection of prompt photon due to the accidental coincidences. The black and blue solid lines presenting the back-to-back annihilation photons might originate from two different decaysBack to article page