The work shows the ability to visualize radiotracers used in SPECT with a system based on a coded aperture mask and a hybrid pixel Timepix detector with the CdTe sensor. Characterization of the system using X-rays and radioactive sources confirms that the spatial resolution of less than 1 mm with a field of view 3 cm × 3 cm can be achieved. The results of a simulation study to determine the expected spatial resolution of the system in the focal plane for the various radionuclides is presented. The possibility of using this system with a thin (1 mm) coded aperture mask for reconstructing images of gamma emitters with the energy up to 180 keV is demonstrated. K: Gamma camera, SPECT, PET PET/CT, coronary CT angiography (CTA); Image reconstruction in medical imaging; Medical-image reconstruction methods and algorithms, computeraided diagnosis; Hybrid detectors 1Corresponding author.

New developments of pixel detectors based on GaAs sensors offer effective registration of the transition radiation (TR) X-rays and perform simultaneous measurements of their energies and emission angles. This unique feature opens new possibilities for particle identification on the basis of maximum available information about generated TR photons. Results of studies of TR energy-angular distributions using a 500 |j.m thick GaAs sensor attached to a Timepix3 chip are presented. Measurements, analysis techniques and a comparison with Monte Carlo (MC) simulations are described and discussed.

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A network of ten GaAs:Cr semiconductor Timepix detectors with GaAs:Cr sensors was installed in the ATLAS cavern at CERN's LHC during the shutdown periods 2015–2016 and 2016–2017 in the framework of a cooperation between ATLAS and the Medipix2 Collaboration. The purpose was to augment the existing system of measuring and characterising the radiation environment in the ATLAS cavern that is based on ATLAS-TPX devices with pixelated silicon sensors. The detectors were in continuous operation during 13 TeV proton-proton collisions in 2017–2018. Data were recorded during proton-proton bunch crossings, and during times without bunch crossings (LHC physics runs) as well as between the physics runs. The overall level of particle radiation as well as the ratio between neutral and charged particles were measured. The detectors recorded all interactions of charge particles, neutrons and photons in GaAs sensors, in which the signal was higher than 6.5 keV in individual pixels. This made it possible to register clusters (tracks) of individual radiation particles interacting in the detectors sensors. During LHC beam-beam collisions, these were all particles represented in the radiation field. In the periods without beam-beam collisions, these were photons and electrons resulting from radioactivity induced during previous collisions in GaAs detectors and in surrounding construction materials, namely by neutrons.

At the end of the 20th century, polymer films with piezoelectric properties were included in the range of active materials used in developing electroacoustic technical methods. For certain purposes and certain conditions of electroacoustic transducer applications, piezoelectric polymer films have considerable advan tages over the widely used piezoelectric ceramics owing to their elasticity, small specific weight, shock resistance, and possibility of fabricating piezoelectric elements with a preset shape [1]. At the same time, the high elasticity, which prevents generation of an intense driving force in these films, restricts the area of appli cation of this material to mainly receiving acoustic sig nals; i.e., to operation in the acoustoelectric or mech anoelectric transformation mode. As for the operation of piezoelectric polymer transducers in the intense radiation mode, they are only effectual for an air medium, where the evident advantage of these trans ducers is their small internal impedance (an order of magnitude smaller than that of piezoceramics) facili tating their matching with the load medium. This property of piezopolymers had been used in a number of sound engineering designs, e.g., in headphones, where the data transfer in a broad frequency band was necessary [2]. However, the transducers used in air for the purposes of communication, signalling, detection and ranging, etc., should have a sufficiently high radi ation intensity to transmit the signals the required dis tances. Both of the aforementioned qualities, namely, the broad bandwidth and the high radiation intensity, depend on the properties of the piezoactive material, as well as on the structure of the transducer.The purpose of our study was to investigate the pos sibility of constructing a low frequency ultrasonic radiator for operation in air on the basis of piezoelec tric polymer films. We experimentally verified the lin earity of the electromechanical properties of the active material, since this linearity was necessary for the operation of a radiating transducer with a sufficiently high intensity. We measured the elastic modulus Y 11 , the longitudinal wave velocity the absorption coef ficient, the permittivity, and the piezoelectric moduli d 31 and е 31 as functions of the driving field. (Here and below, axis 1 is directed along the orientation, i.e., direction of tension, of the piezoelectric film; axis 3 is directed along the width of the piezoelectric film, i.e., the electric polarization direction; and axis 2 is per pendicular to the two aforementioned axes.) The objects of our measurements were a Russian made uniaxially oriented piezoelectric film of the F2ME type [3] and a commercial piezoelectric film made by the MSI company (United States). The driving field intensity was increased from 10 5 to 5 × 10 6 V/m, the latter value corresponding to half the breakdown field for the F2ME film. In this case, the stress amplitude at resonance reached values that exceeded 5 × 10 6 N/m 2 and were close to the onset of the yield of the mate...