Gamma ray detection system and calibration method thereof

A method of calibrating a gamma ray detection system comprising a computation system including a signal processing and control system, a detection module assembly including at least one detection module configured for detecting gamma ray emissions from a target zone, each detection module comprising at least one monolithic scintillator plate having a major surface oriented to generally face the target zone and lateral minor surfaces defining edges of the scintillator layer, and a plurality of photon detectors coupled to edges of said at least one monolithic scintillator plate and connected to the signal processing and control system, the scintillator plate comprising a material having isotopes intrinsically emitting radiation causing intrinsic scintillation events having an intensity measurable by the photon detectors, wherein the method comprises detecting an intensity and time of a plurality of said intrinsic scintillation events by the plurality of photon detectors, transmitting values of said detected intensities and times of scintillation events output by the plurality of photon detectors to a computing system, and executing a calibration module program in the computing system to determine spatial positions of scintillating events in the monolithic scintillator plate as a function of the outputs of the photon detectors.