KEYWORDS: Photons, RGB color model, Resistors, Signal detection, Quantum efficiency, Single photon detectors, Silicon photomultipliers, Avalanche photodiodes, Single photon, Photodetectors, Physics, Spectroscopy, High dynamic range imaging, Sensors, Photon counting
Silicon photomultipliers (SiPMs) are arrays of many single-photon avalanche diodes (SPADs), all connected in parallel. Each SPAD is sensitive to single photons and the SiPM gives an output proportional to the number of detected photons. These sensors are becoming more and more popular in different applications, from high-energy physics to spectroscopy, and they have been significantly improved over last years, decreasing the noise, increasing the cell fill-factor (FF) and thus achieving very high photon-detection efficiency (PDE). In FBK (Trento, Italy), we developed new SiPM technologies with high-density (HD) and, more recently, ultra-high-density (UHD) of cells (i.e. density of SPADs). These technologies employ deep-trenches between cells, for electrical and optical isolation. As an extreme case the smallest-cell, SiPM, i.e. with 5μm cell pitch, has about 40000 SPADs per squared millimeter. Such small SPAD dimensions gives a significantly high dynamic range to the SiPM. These small-cells SiPM have a lower correlated noise (including lower afterpulsing probability) and a faster recharge time (in the order of few nanoseconds), and they also preserve a very good detection efficiency (despite the small SPAD dimension).
S. N. Zhang, M. Feroci, A. Santangelo, Y. W. Dong, H. Feng, F. J. Lu, K. Nandra, Z. S. Wang, S. Zhang, E. Bozzo, S. Brandt, A. De Rosa, L. J. Gou, M. Hernanz, M. van der Klis, X. D. Li, Y. Liu, P. Orleanski, G. Pareschi, M. Pohl, J. Poutanen, J. L. Qu, S. Schanne, L. Stella, P. Uttley, A. Watts, R. Xu, W. F. Yu, J. J. M. in ’t Zand, S. Zane, L. Alvarez, L. Amati, L. Baldini, C. Bambi, S. Basso, S. Bhattacharyya, R. Bellazzini, T. Belloni, P. Bellutti, S. Bianchi, A. Brez, M. Bursa, V. Burwitz, C. Budtz-Jørgensen, I. Caiazzo, R. Campana, X. L. Cao, P. Casella, C. Y. Chen, L. Chen, T. Chen, Y. Chen, M. Civitani, F. Coti Zelati, W. Cui, Z. G. Dai, E. Del Monte, D. de Martino, S. Di Cosimo, S. Diebold, M. Dovciak, I. Donnarumma, V. Doroshenko, P. Esposito, Y. Evangelista, Y. Favre, P. Friedrich, F. Fuschino, J. Galvez, Z. Gao, M. Ge, O. Gevin, D. Goetz, D. Han, J. Heyl, J. Horak, W. Hu, F. Huang, Q. S. Huang, R. Hudec, D. Huppenkothen, G. L. Israel, A. Ingram, V. Karas, D. Karelin, P. Jenke, L. Ji, S. Korpela, D. Kunneriath, C. Labanti, G. Li, X. Li, Z. S. Li, E. W. Liang, O. Limousin, L. Lin, Z. X. Ling, H. B. Liu, H. Liu, Z. Liu, B. Lu, N. Lund, D. Lai, B. Luo, T. Luo, B. Ma, S. Mahmoodifar, M. Marisaldi, A. Martindale, N. Meidinger, Y. P. Men, M. Michalska, R. Mignani, M. Minuti, S. Motta, F. Muleri, J. Neilsen, M. Orlandini, A. T. Pan, A. Patruno, E. Perinati, A. Picciotto, C. Piemonte, M. Pinchera, A. Rachevski, M. Rapisarda, N. Rea, E. M. Rossi, A. Rubini, G. Sala, X. W. Shu, C. Sgro, Z. X. Shen, P. Soffitta, L. Song, G. Spandre, G. Stratta, T. Strohmayer, L. Sun, J. Svoboda, G. Tagliaferri, C. Tenzer, T. Hong, R. Taverna, G. Torok, R. Turolla, S. Vacchi, J. Wang, D. Walton, K. Wang, J. F. Wang, R. J. Wang, Y. Wang, S. Weng, J. Wilms, B. Winter, X. Wu, S. L. Xiong, Y. Xu, Y. Xue, Z. Yan, S. Yang, X. Yang, Y. J. Yang, F. Yuan, W. Yuan, Y. F. Yuan, G. Zampa, N. Zampa, A. Zdziarski, C. Zhang, C. L. Zhang, L. Zhang, X. Zhang, Z. Zhang, W. Zhang, S. Zheng, P. Zhou, X. Zhou
eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary goals are the determination of the equation of state of matter at supra-nuclear density, the measurement of QED effects in highly magnetized star, and the study of accretion in the strong-field regime of gravity. Primary targets include isolated and binary neutron stars, strong magnetic field systems like magnetars, and stellar-mass and supermassive black holes. The mission carries a unique and unprecedented suite of state-of-the-art scientific instruments enabling for the first time ever the simultaneous spectral-timing-polarimetry studies of cosmic sources in the energy range from 0.5-30 keV (and beyond). Key elements of the payload are: the Spectroscopic Focusing Array (SFA) - a set of 11 X-ray optics for a total effective area of ∼0.9 m2 and 0.6 m2 at 2 keV and 6 keV respectively, equipped with Silicon Drift Detectors offering <180 eV spectral resolution; the Large Area Detector (LAD) - a deployable set of 640 Silicon Drift Detectors, for a total effective area of ∼3.4 m2, between 6 and 10 keV, and spectral resolution better than 250 eV; the Polarimetry Focusing Array (PFA) – a set of 2 X-ray telescope, for a total effective area of 250 cm2 at 2 keV, equipped with imaging gas pixel photoelectric polarimeters; the Wide Field Monitor (WFM) - a set of 3 coded mask wide field units, equipped with position-sensitive Silicon Drift Detectors, each covering a 90 degrees x 90 degrees field of view. The eXTP international consortium includes major institutions of the Chinese Academy of Sciences and Universities in China, as well as major institutions in several European countries and the United States. The predecessor of eXTP, the XTP mission concept, has been selected and funded as one of the so-called background missions in the Strategic Priority Space Science Program of the Chinese Academy of Sciences since 2011. The strong European participation has significantly enhanced the scientific capabilities of eXTP. The planned launch date of the mission is earlier than 2025.
Current research in the field of positron emission tomography (PET) focuses on improving the sensitivity of the scanner with thicker detectors, extended axial field-of-view, and time-of-flight (TOF) capability. These create the need for depth-of-interaction (DOI) encoding to correct parallax errors. We have proposed a method to encode DOI using phosphor-coated crystals. Our initial work using photomultiplier tubes (PMTs) demonstrated the possibilities of the proposed method, however, a major limitation of PMTs for this application is poor quantum efficiency in yellow light, corresponding to the wavelengths of the converted light by the phosphor coating. In contrast, the red-green-blue-high-density (RGB-HD) silicon photomultipliers (SiPMs) have a high photon detection efficiency across the visible spectrum. Excellent coincidence resolving time (CRT; <210 ps) was obtained by coupling RGB-HD SiPMs and 3 × 3 × 20 mm3 lutetium fine silicate crystals coated on a third of one of their lateral sides. Events were classified in three DOI bins (∼6.7-mm width) with an average sensitivity of 83.1%. A CRT of ∼200 ps combined with robust DOI encoding is a marked improvement in the phosphor-coated approach that we pioneered. For the first time, we read out these crystals with SiPMs and clearly demonstrated the potential of the RGB-HD SiPMs for this TOF-DOI PET detector.
A scintillation gamma-ray detector, composed of a commercial 0.5" thick, 0.5" diameter LaBr3(Ce) crystal coupled to a 7-cell hexagonal Silicon Drift Detector has been developed and tested. The characterization with X-rays and gamma rays is presented and discussed also within the context of the optical properties of the readout system. A final comparison between our results and state of the art is also discussed in order to propose this prototype for astrophysical applications.
A future compact and modular X and gamma-ray spectrometer (XGS) has been designed and a series of proto- types have been developed and tested. The experiment envisages the use of CsI scintillator bars read out at both ends by single-cell 25 mm2 Silicon Drift Detectors. Digital algorithms are used to discriminate between events absorbed in the Silicon layer (lower energy X rays) and events absorbed in the scintillator crystal (higher energy X rays and -rays). The prototype characterization is shown and the modular design for future experiments with possible astrophysical applications (e.g. for the THESEUS mission proposed for the ESA M5 call) are discussed.
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