Gaseous photodetectors with solid photocathodes
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seous Photodetectors with Solid Photocathodes A. F. Buzulutskov Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia e-mail: [email protected] Abstract—Remarkable properties of gas photodetectors make them attractive for application in high energy physics, astrophysics, and medical imaging. This review presents the results of research and development of gaseous photodetectors with solid photocathodes (GPDs). In particular, efficient photocathodes for the ultraviolet (mainly CsI) and the visible ranges, including photocathodes with protective dielectric nanofilms, are described. Some problems of the physics of gaseous photodetectors and photocathodes are considered: photoelectron backscattering in gas, photoemission amplification in an electric field, photoelectron transport through nanofilms, protective properties of nanofilms, and photon and ion feedback. A separate section is devoted to GPDs based on gas electron multipliers (GEMs), including sealed GPDs and cryogenic two-phase avalanche detectors with CsI photocathodes. PACS numbers: 29.40.Cs; 85.60.Ha DOI: 10.1134/S1063779608030052
INTRODUCTION Detectors of photons (photodetectors) are one of the basic types of detectors in high energy and nuclear physics. They are used in fields in which the optical method of signal detection is required, namely, in scintillation counters, Cherenkov counters, ring imaging Cherenkov detectors (RICH detectors), scintillation calorimeters, and so on. The most widespread representatives of photodetectors are vacuum photoelectron multipliers (PMT) and semiconductor photodiodes. At the same time, gaseous photodetectors sensitive to single photons which use the principle of avalanche amplification in gases (see, e.g., [1, 2]) have been developed for over a quarter of a century. The advantages of gaseous photodetectors when compared to vacuum ones are a large working area, convenient methods for coordinate information readout, and the capability of operating in a magnetic field, and their advantages over semiconductor detectors are a lower noise level and higher gain. As regards such parameters as amplitude and time resolution, they yield to vacuum photodetectors. Thus, the specific field of application of gaseous photodetectors is determined by the tasks in which coordinate photodetectors with relatively large area (more than one square decimeter) are required. Although photosensitive gaseous counters were known long ago [3–5], the first large-area coordinate gaseous photodetectors were developed in the early 1980s in connection with the development of RICH detectors [1]. They had a gaseous photocathode, i.e., operated using vapors of organic substances with low ionization potential sensitive in the ultraviolet range, such as TEA and TMAE [1]. The field of application of photodetectors with gaseous photocathodes, however, is quite limited for a number of reasons. These reasons are their insensitivity to visible light, incapability of
operation at cryogenic temperatures, and imp
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