Performance evaluation of novel LaBr₃(Ce) scintillator geometries for fast-timing applications

We evaluate the performance of two LaBr₃(Ce) crystals that were produced with special geometries, aimed at enhancing the scintillation light collection and thus the time resolution. Their design was motivated by the construction of high-performance fast-timing arrays like the FAst TIMing array for DESPEC (FATIMA), which demands a high packing factor in addition to good time and energy resolutions. Energy resolution and efficiency were measured using standard calibration sources. Timing measurements were performed at ⁶⁰Co and ²²Na γ-energies against a fast BaF₂ reference detector. The time resolution was optimized by the choice of the photomultiplier bias voltage and the fine tuning of the constant fraction discriminator parameters. Monte Carlo simulations using the Geant4 toolkit were performed in order to achieve a better understanding of how the new geometries affect the light transport and thus the performance of the crystals. It is found that the conical-shaped LaBr₃(Ce) crystals are optimal for fast-timing applications and for the construction of arrays such as FATIMA.