AUTHOR=Pots Rosalinde Hendrika , Auffray Etiennette , Gundacker Stefan 

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

JOURNAL=Frontiers in Physics

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2020.592875

DOI=10.3389/fphy.2020.592875

ISSN=2296-424X

ABSTRACT=<p>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 <inline-formula id="inf2"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula> scintillator with deep ultraviolet-sensitive silicon photomultipliers (SiPMs) from Hamamatsu for precise timing in PET and HEP. Using small <inline-formula id="inf3"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula> 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 <inline-formula id="inf4"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>±</mml:mo></mml:math></inline-formula> 5 ps full width at half maximum (FWHM) is achieved when coupling with air. This figure improves to 78 <inline-formula id="inf5"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>±</mml:mo></mml:math></inline-formula> 4 ps FWHM when coupling the <inline-formula id="inf6"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula> crystal with UV transparent optical grease, Viscasil, to the photodetector. This CTR performance obtained with <inline-formula id="inf7"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula> 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 <inline-formula id="inf8"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">Ba</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math></inline-formula>, one could imagine the development of sub-30 ps FWHM time-of-flight-PET systems.</p>