Energy calibration of LaBr₃ detectors using inherent radioactivity

In general, the energy calibration of gamma-ray detectors is carried out by using radioactive sources with well-known emission lines. The fact that the scintillator material LaBr 3 includes natural radioactivity is often taken advantage of to perform an energy calibration without the need to handle an external radioactive source. For this purpose, the emission energy of photons to be detected in peaks has to be well known. Though the energies of the emission lines of the relevant isotope 138 La and further information on radioactive contaminations are published with high precision, there are inconsistencies in the literature concerning the effective energies of observed photon peaks caused by inherent radioactivity. In this article, the actual peak positions are published as a result of high-precision measurements. The potential and limitations of an energy calibration of LaBr 3 detectors based on the inherent radioactivity are discussed, as the emission lines of 138 La are detected in clusters rather than single, clearly defined lines.