Fig. 2

Normalized energy spectra of single events recorded from ¹⁸F (pure β⁺ emitter, red) and the ⁶⁸Ga (non-pure β⁺ emitter, blue) shown in linear (a) and logarithmic (b) scales. The green and orange boxes represent the energy windows set at (350, 700) and (750, 2000) keV to distinguish between photopeak (low energy) and high-energy events. The events recorded in the high-energy window are relatively higher for ⁶⁸Ga than for ¹⁸F compared with the event recorded in the photopeak