A γ-Ray Detector Based on a 3” LaBr3:Ce:Sr Crystal With SiPM Readout for 80 keV–16 MeV Energy Range With Position Sensitivity for Doppler Correction

We report the validation in an extended energy range (80 keV –≃ 16 MeV) of the GAMMA detector, a high-dynamic-range, high-resolution, gamma-ray spectrometer for nuclear physics applications based on a 3" co-doped lanthanum bromide (LaBr ₃ :Ce:Sr) crystal (73 ph/keV conversion efficiency, 25 ns decay time) coupled to 144 NUV-HD Silicon Photomultipliers (SiPMs). The detector shows state-of-the-art energy resolution along the entire range thanks to the automatic gain switching feature (Adaptive Gain Control, AGC) of the custom ASICs employed in the system. To the best of our knowledge, this is the first time that SiPMs have been used to measure such high energy together with a wide dynamic range and excellent energy resolution (2.7% at 662 keV). In addition, the pixelated nature of the SiPMs detectors, combined with Machine Learning algorithms, can be exploited to reconstruct the position of the first interaction of the gamma rays inside the scintillation crystal. Previous measurements with a ¹³⁷ Cs collimated source have achieved a spatial resolution better than 2 cm. This performance in position sensitivity has been used to compensate for the relativistic Doppler broadening effects of gamma rays at 15.110(3) MeV emitted by a carbon nucleus moving at relativistic speed (v/c ≃ 0.05) resulting from a boron-on-deuterium reaction, improving the FWHM resolution of the peak by 15%, which is in agreement with the theoretical expectation.