The scintillation detector assembly 10 comprises a first scintillation detector 11A of a set SSD of scintillation detectors 11, comprising a first scintillator 12A of a set SS of scintillators 12 and a first light sensor 13A of a set SLS of respective light sensors 13 optically coupled thereto, arranged to detect electromagnetic radiation and output a first signal; a first radiation source 14A of a set SRS of radiation sources 14, configured to emit first gamma radiation G1 of a first set SG of gamma radiation G, having a first reference energy RE1 of a set SRE of respective first reference energies RE; and a controller 15 configured to control a gain of the first scintillation detector 11A based, at least in part, on the first gamma radiation, having the first reference energy, detected by the first scintillation detector 11A.