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Register a new userDesign considerations for a new generation of SiPMs with unprecedented timing resolution
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Scientific Information Service CERN
Publication date
2021
fields
Physics
and research's language is
English
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The potential of photon detectors to achieve precise timing information is of increasing importance in many domains, PET and CT scanners in medical imaging and particle physics detectors, amongst others. The goal to increase by an order of magnitude the sensitivity of PET scanners and to deliver, via time-of-flight (TOF), true space points for each event, as well as the constraints set by future particle accelerators require a further leap in time resolution of scintillator-based ionizing radiation detectors, reaching eventually a few picoseconds resolution for sub MeV energy deposits. In spite of the impressive progress made in the last decade by several manufacturers, the Single Photon Time Resolution (SPTR) of SiPMs is still in the range of 70-120ps FWHM, whereas a value of 10ps or even less would be desirable. Such a step requires a break with traditional methods and the development of novel technologies. The possibility of combining the extraordinary potential of nanophotonics with new approaches offered by modern microelectronics and 3D electronic integration opens novel perspectives for the development of a new generation of metamaterial-based SiPMs with unprecedented photodetection efficiency and timing resolution.
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This paper discusses the effects of radiation damage to SiPMs on the performances of plastic scintillator counters with series-connected SiPM readout, focusing on timing measurements. The performances of a counter composed of a $120 times 40 times5~mathrm{mm}^3$ scintillator tile read out by two sets of six SiPMs from AdvanSiD connected in series attached on the short sides are presented, for different combinations of SiPMs at various levels of irradiation. Firstly, six SiPMs were equally irradiated with electrons from $^{90}$Sr sources up to a fluence of $Phi_mathrm{e^-}approx 3 times 10^{12}~mathrm{cm}^{-2}$. The timing resolution of the counter gradually deteriorated by the increase in dark current. The dark current and the deterioration were reduced when the counter was cooled from 30$^circ$C to 10$^circ$C. Secondly, 33 SiPMs were irradiated with reactor neutrons. The characteristics of counters read out by series-connected SiPMs with non-uniform damage levels, were investigated. The signal pulse height, the time response, and the timing resolution depend on the hit position in the counter, when SiPMs irradiation is not uniform.
In this paper, the authors investigate a number of design and market considerations for an axial flux superconducting electric machine design that uses high temperature superconductors. This work was carried out as part of the University of Cambridges Centre for Entrepreneurial Learning ETECH Project programme, designed to accelerate entrepreneurship and diffusion of innovations based on early stage and potentially disruptive technologies from the University. The axial flux machine design is assumed to utilise high temperature superconductors in both wire (stator winding) and bulk (rotor field) forms, to operate over a temperature range of 65-77 K, and to have a power output in the range from 10s of kW up to 1 MW (typical for axial flux machines), with approximately 2-3 T as the peak trapped field in the bulk superconductors. The authors firstly investigate the applicability of this type of machine as a generator in small- and medium-sized wind turbines, including the current and forecasted market and pricing for conventional turbines. A study is also carried out on the machines applicability as an in-wheel hub motor for electric vehicles. Some recommendations for future applications are made based on the outcome of these two studies. Next, the cost of YBCO-based superconducting (2G HTS) wire is analysed with respect to competing wire technologies and compared with current conventional material costs. Current wire costs for both 1G and 2G HTS are still too great to be economically feasible for such superconducting devices, but round wire, so-called 3G HTS, conductors may be a promising new option with a view to the future. Finally, different cooling options are assessed for the machine design and the analysis suggests that waiting for the maturation of pulse-tube cooling technology may be the best option for this particular application.
Measurement of the Time-of-Flight (TOF) of the 511 keV gammas brings an important reduction of statistical noise in the PET image, with higher precision time measurements producing clearer images. Scintillating crystals are used to convert the 511 keV annihilation photon to an electron of ~511 KeV energy via the photoelectric effect; it is necessary to determine with precision the position and time of this conversion within the scintillating crystal. We propose using an array of crystals cut into a specific geometry discussed below; these crystals are read out by an array of strip SiPMs. This technique allows individual time measurements of the first arriving photo-electrons and to extract the best time resolution using a specific algorithm. The final result is a precise determination of the 3D position (that includes the depth of interaction) of the photoelectric interaction and an improved time measurement.
We give an analytic treatment of the time resolution and efficiency of Single Photon Avalanche Diodes (SPADs) and Silicon Photomultipliers (SiPMs). We provide closed-form expressions for structures with uniform electric fields and efficient numerical prescriptions for arbitrary electric field configurations. We discuss the sensor performance for single photon detection and also for charged particle detection.
The design and tests of Timing Counter elements for the upgrade of the MEG experiment, MEG II,is presented. The detector is based on several small plates of scintillator with a Silicon PhotoMultipliers dual-side readout. The optimisation of the single counter elements (SiPMs, scintillators, geometry) is described. Moreover, the results obtained with a first prototype tested at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati (LNF) are presented.
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