Recent developments in gamma-ray spectroscopy with new scintillators, LaBr3(Ce), to investigate nuclear structure at high excitation and far from stability

Lanthanum bromide scintillators are among the new most promising detectors for nuclear spectroscopy experiments. Their relevant performances in terms of energy resolution, time resolution and high density make them a suitable alternative even with respect to germanium-based solid-state detectors, which, on the other side, are more expensive and difficult to operate. However, the huge amount of optical photons emitted in burst by cerium-doped lanthanum bromide scintillators poses severe constraints on the specifications of photomultipliers, namely they must operate at very large instantaneous current values with minimum saturation of output pulse signals. We analyse the effects of output signal saturation in photomultiplier tubes as a function of the power supply high voltage level and the amount of energy released in the scintillator crystal and propose a simple model to characterize this very complex phenomenon. According to the proposed model, a preliminary first-order correction has been extracted. This technique reduces the non-linear response of a LaBr 3(Ce) scintillator by almost an order of magnitude for γ-rays of 9MeV.