Detailed analysis of a previously uninvestigated feature in lanthanum bromide scintillation crystals intrinsic background

Lanthanum halide scintillation crystals represent the state of the art of the scintillators technology for gamma ray spectroscopy. They feature a short decaying time (<30ns), high light yield, good detection efficiency and an optimal energy resolution (<2.9% at 662keV). Lanthanum halides also present an intense intrinsic background caused by the radioactive decay of 138La and 227Ac contaminations, which cover all the lower energies up to 3MeV. Despite being a limitation in low counting rate experiments, this intrinsic background can be exploited to perform energy calibration of the pulse height spectra, refraining from the employment of dedicated external sources. The intense electron capture peak of 138La at 1471keV, which is the most relevant feature for this purpose, has been deeply characterized in literature in many aspects. In this work, a detailed analysis of the lanthanum bromide intrinsic background was performed on several scintillation crystals, unveiling a feature with an average energy of 1515keV not yet described in the current literature.