Fig. 7
From: Efficiency determination of J-PET: first plastic scintillators-based PET scanner
a The sum of the two smallest versus their differences angular correlations between the registered 3 hits are plotted event-wise. The number of events in a given pixel is shown in a logarithmic scale. The vertical white dashed lines indicate the region around 180 degree selected as events corresponding to two primary back to back 511 keV photons (\(\alpha +\beta\) = 180\(^0\)) and one scatter photon. b Shows the results of the calculated scatter test. The elliptical dashed red lines show the regions used to assign the scattered photon (3 in Fig. 6) to the primary photon. The maximum centered around coordinate \((-2,0)\) indicates the events when photon 2 was scattered, while the maximum centered around \((0,-2)\) corresponds to the events in which photon 1 was scattered