Improving the Time Resolution of Large-Area LaBr[sub.3]:Ce Detectors with SiPM Array Readout

• Published in: Condensed matter Vol. 8; no. 4
• Main Authors: Bonesini, Maurizio, Bertoni, Roberto, Abba, Andrea, Caponio, Francesco, Prata, Marco, Rossella, Massimo
• Format: Journal Article
• Language: English
• Published: MDPI AG 01.11.2023
• Subjects: Detectors; National security
• ISSN: 2410-3896; 2410-3896
• DOI: 10.3390/condmat8040099

LaBr[sub.3]:Ce crystals have good scintillation properties for X-ray spectroscopy. Initially, they were introduced for radiation imaging in medical physics with either a photomultiplier or SiPM readout, and they found extensive applications in homeland security and gamma-ray astronomy. We used 1[sup.″] round LaBr[sub.3]:Ce crystals to realize compact detectors with the SiPM array readout. The aim was a good energy resolution and a fast time response to detect low-energy X-rays around 100 keV. A natural application was found inside the FAMU experiment, at RIKEN RAL. Its aim is a precise measurement of the proton Zemach radius with impinging muons, to contribute to the solution to the so-called “proton radius puzzle”. Signals to be detected are characteristic X-rays around 130 KeV. A limit for this type of detector, as compared to the ones with a photomultiplier readout, is its poorer timing characteristics due to the large capacity of the SiPM arrays used. In particular, long signal falltimes are a problem in experiments such as FAMU, where a “prompt” background component must be separated from a “delayed” one (after 600 ns) in the signal X-rays to be detected. Dedicated studies were pursued to improve the timing characteristics of the used detectors, starting from hybrid ganging of SiPM cells; then developing a suitable zero pole circuit with a parallel ganging, where an increased overvoltage for the SiPM array was used to compensate for the signal decrease; and finally designing ad hoc electronics to split the 1[sup.″] detector’s SiPM array into four quadrants, thus reducing the involved capacitances. The aim was to improve the detectors’ timing characteristics, especially falltime, while keeping a good FWHM energy resolution for low-energy X-ray detection.