A calibration source for a gamma-
ray spectrometer is provided. The calibration source comprises a
scintillator body having a cavity in which a radioactive material is received. The
scintillator body may be generally cuboid and the cavity may be formed by a hole drilled into the
scintillator body. The radioactive material comprises a radioactive
isotope having a decay transition associated with emission of a
radiation particle and a gamma-
ray having a known energy e.g. Na-22. A
photodetector, for example a
silicon photomultiplier, is optically coupled to the scintillator body and arranged to detect
scintillation photons generated when
radiation particles emitted from the radioactive material interact with the surrounding scintillator bod. A gating circuit is arranged to receive detection signals from the
photodetector and to generate corresponding gating signals for a
data acquisition circuit of an associated gamma-
ray spectrometer to indicate that gamma-ray detections in the gamma-ray
spectrometer occurring within a time window defined by the gating
signal are associated with a decay transition in the radioactive
isotope. Thus a calibration source is provided based around a simple scintillator body design. Furthermore, the radioactive material may be introduced into the scintillator body in a separate step after manufacture of the scintillator body, thereby reducing the risk of
radioactive contamination during manufacture.