In this study, we re-evaluated the attainable coincidence time resolution (CTR) performance for 3×3×3 mm3 LYSO crystals coupled to matched 3×3 mm2 SiPMs. This work was motivated by potential increased sensitivity in brain positron emission tomography (PET) detector blocks that would be enabled with ultrashort CTR (<100 ps). The recent progress in silicon photomultiplier (SiPM) technology, high-frequency read-out circuits, and optimized data processing is expected to lead directly to improved performance. The 3×3×3 mm3 LYSO crystals, with all sides polished to optical quality, were optically coupled to SiPMs designed and fabricated by Fondazione Bruno Kessler (FBK). An improved high frequency read-out circuit was designed and fabricated. CTR was measured using a 22Na positron source (<10 μCi) sandwiched between two identical LYSO/SiPM/read-out circuit stacks. Our studies show that a CTR of less than 80 ps, which, to the best of our knowledge, is the shortest reported CTR for 3×3×3 mm3 LYSO crystals. The results demonstrate, for the first time, that CTR performance in 3×3×3 mm3 LYSO crystals coupled to a 3mm×3mm2 SiPMs is comparable to CTRs achieved for ultra-small LYSO crystals (2×2×3 mm3) coupled to large 4 × 4 mm2 SiPMs. These results prove that an array of 3×3×3 mm3 LYSO/SiPM can be used to build a next generation high performance detector block with very high packing fraction, enabling ultimately very high gamma ray detection efficiency and very high system sensitivity.
The Cherenkov Telescope Array1 (CTA) is the next-generation ground-based observatory for very-high-energy gamma rays. The CTA consists of three types of telescopes with different mirror areas to cover a wide energy range (20 GeV–300 TeV) with an order of magnitude higher sensitivity than the predecessors. Among those telescopes, the Large-Sized Telescope (LST) is designed to detect low-energy gamma rays between 20 GeV and a few TeV with a 23 m diameter mirror. To make the most of such a large light collection area (about 400 m2), the focal plane camera must detect as much reflected Cherenkov light as possible. We have developed each camera component to meet the CTA performance requirements for more than ten years and performed quality-control tests before installing the camera to the telescope.2, 3 The first LST (LST-1) was inaugurated in October 2018 in La Palma, Spain (Figure 1).4 After the inauguration, various calibration tests were performed to adjust hardware parameters and verify the camera performance. In parallel, we have been developing the analysis software to extract physical parameters from low-level data, taking into account some intrinsic characteristics of the switched capacitor arrays, Domino Ring Sampler version 4 (DRS4), used for sampling the waveform of a Cherenkov signal. In this contribution, we describe the hard- ware design of the LST camera in Section 2, a procedure for low-level calibration in Section 3, and the readout e of the LST camera after the hardware calibration with a dedicated analysis chain in Section 4.
The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mCrab celestial object between the energy-range 25–80 keV in one 6 hour flight. Polarization measurements in soft gamma-rays are expected to provide a powerful probe into high-energy emission mechanisms in/around neutron stars, black holes, supernova remnants, active-galactic nuclei etc. The “pathfinder” flight was performed in July 2013 for 14 days from Sweden to Russia. The polarization is measured using Compton scattering and photoelectric absorption in an array of 61 well-type phoswich detector cells (PDCs) for the pathfinder instrument. The PDCs are surrounded by 30 BGO crystals which form a side anti-coincidence shield (SAS) and passive polyethylene neutron shield. There is a neutron detector consisting of LiCaAlF6 (LiCAF) scintillator covered with BGOs to measure the background contribution of atmospheric neutrons. The data acquisition system treats 92 PMT signals from 61 PDCs + 30 SASs + 1 neutron detector, and it is developed based on SpaceWire spacecraft communication network. Most of the signal processing is done by digital circuits in Field Programmable Gate Arrays (FPGAs). This enables the reduction of the mass, the space and the power consumption. The performance was calibrated before the launch.
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