Exploiting Cross-Luminescence in BaF2 for Ultrafast Timing Applications Using Deep-Ultraviolet Sensitive HPK Silicon Photomultipliers

Abstract

Time resolution of scintillation-based detectors is becoming continuously more important, both for medical applications, especially in positron emission tomography (PET), and in high energy physics. This article is an initial study on exploiting the fast cross-luminescence emission in the inorganic BaF 2 scintillator with deep ultraviolet-sensitive silicon photomultipliers (SiPMs) from Hamamatsu for precise timing in PET and HEP. Using small BaF 2 pixels optimized for timing read out by these photodetectors with a photon detection efficiency (PDE) of only about 15% in the desired 200 nm emission region, a coincidence time resolution (CTR) of 94 ± 5 ps full width at half maximum (FWHM) is achieved when coupling with air. This figure improves to 78 ± 4 ps FWHM when coupling the BaF 2 crystal with UV transparent optical grease, Viscasil, to the photodetector. This CTR performance obtained with BaF 2 is better than that measured with LYSO:Ce, a commonly used state-of-the-art inorganic scintillator in PET, when coupled to another Hamamatsu photodetector (S13360), having a PDE of 60% at 420 nm, with Meltmount. In view of the prospects in advancing technologies for ultraviolet sensitive SiPMs, with high PDE and single photon time resolution, and further advancements in producing high quality BaF 2 , one could imagine the development of sub-30 ps FWHM time-offlight-PET systems.

Vacuum ultraviolet silicon photomultipliers applied to BaF2 cross-luminescence detection for high-rate ultrafast timing applications

“…In Pots et al (2020) several TCSPC measurements under x-ray excitation of BaF 2 samples from Proteus and Epic Crystal have been performed, placing different filters between the BaF 2 crystal and the single-photon detector, a Becker & Hickl hybrid-PMT. It was found that by placing a high-pass filter of 400 nm (cutting all wavelengths larger than 400 nm) no scintillation emission was recorded.…”

Analysis and comparison of the Core-to-Valence Luminescence mechanism in a large CLYC crystal under neutron and γ-ray irradiation through optical filtering selection of the scintillation light

“…The different experiments performed using the 7 Li enriched crystal and the Asahi optical filter allowed precisely characterizing the material scintillation process. The wavelength-resolved RL results obtained with different photon energies allowed verifying that there is no LET-dependence of the CLYC emission in the range 0.5-5 keV/μm, i.e.…”

“…The measurements were performed with a 1-inch right cylinder CLYC scintillator enriched in 7 Li to > 99%, purchased from Radiation Monitoring Devices [18]. The crystal is hygroscopic and therefore encapsulated in an aluminum housing provided with a single quartz window.…”

“…CLYC rather good -ray spectrometry capabilities are due to its density (3.3 g/cm 3 ), Zeff (54) and energy resolution, about 5% at 662 keV [1,2]. Its fast neutron spectrometry properties were recently demonstrated for 7 Li enriched crystals [3,4]. The reactions involved are 35 Cl(n,p) 35 S and 35 Cl(n,α) 32 P below 15 MeV.…”

“…The consequent hole produced in the core band recombines with an electron of the valence band. Since the valence band is filled with electrons, the recombination probability is large resulting in a fast process [7]. The CVL is a competitive radiative de-excitation process with a decay time faster than that of the other three scintillation mechanisms present in CLYC, described below [8,9].…”