Development of a 3D imaging calorimeter in lanthanum bromide for gamma-ray space astronomy

The new generation of high light-output inorganic scintillators i.e. cerium-doped lanthanum(III) bromide (LaBr₃:Ce) show a promising future in application as a space-based γ-ray calorimeter. Its internal qualities such as good energy resolution or radiation tolerance are well suited for detection of γ-rays in the MeV range, thus providing access to, so far, understudied questions in physics of nucleosynthesis, the active Sun or astrophysical compact objects. For this purpose, under the project of creating a new Compton telescope prototype, we have studied the response of a detection module comprising a 5×5 cm² area and 1 cm thick LaBr₃:Ce crystal scintillator coupled to a 64 channel multi-anode photomultiplier read out by the ASIC MAROC. Measurements with various radioactive sources have been compared with detailed GEANT4 simulations that include the tracking of the near-UV photons produced in the scintillation crystal. The localization of the first interaction point of incident γ-rays have been studied from the measured charge distributions using an artificial neural network. Together with the other measured properties, the position resolution that we obtain makes this detector module very interesting for the next generation of space telescopes operating in the medium-energy γ-ray domain.