Abstract
The use of photon-counting detectors (PCD) in X-ray computed
tomography (CT) allows for obtaining specific spectral information
about the materials present in the studied object. This ...provides the
capability to detect contrast agents (CAs) based on elements with
high atomic numbers, which opens up significant prospects for
diagnostics and preclinical trials. This work presents a criterion
for the extraction of a contrast agent and the determination of its
concentration based on the K-edge absorption. The criterion is built
on the study of the spectral characteristics of CAs. It considers
scenarios where more than two contrast agents are simultaneously
used in a wide range of concentrations in the study. The experiment
was conducted using a laboratory microtomographic system based on
the Medipix3RX detector family. The criterion utilizes five energy
thresholds for the identification of a single contrast
agent. Lanthanides were used as contrast agents.
The hybrid pixel detector technology brought to the X-ray imaging a low noise level at a high spatial resolution, thanks to the single photon counting. However, silicon as the most widespread ...detector material is marginally sensitive to photons with energies above 30 keV. Therefore, the high-Z alternatives to silicon such as gallium arsenide and cadmium telluride are increasingly attracting attention of the community for the development of X-ray imaging systems. The results of our investigations of the Timepix detectors bump bonded to sensors made of gallium arsenide compensated by chromium (GaAs:Cr) are presented in this work. The following properties are most important from the practical point of view: the IV characteristics, the charge transport characteristics, photon detection efficiency, operational stability, homogeneity, temperature dependence, as well as energy and spatial resolution are considered. The applicability of these detectors for spectroscopic X-ray imaging is discussed.
Investigation of the semiconductor detectors properties under neutron irradiation is very important for their practical application. High-resistivity gallium arsenide detectors (GaAs:Cr) were ...irradiated with various fast neutron fluences in range from 3.9×10n cm−2 to 3.7×1016 cm−2 at the IBR-2 reactor, FLNP, JINR. The neutron fluence was measured by placing silicon planar detectors at the measured points and measuring the 1 MeV (Si) equivalent fast neutron fluence. The charge collection efficiency and the current-voltage characteristics of irradiated detectors were measured, and their degradation after neutron irradiation was compared with the results obtained by irradiation with 21 MeV electrons.
Growing energies of particles at modern or planned particle accelerator experiments as well as cosmic ray experiments require particle identification at gamma-factors (γ) of up to ∼105. At present ...there are no detectors capable of identifying charged particles with reliable efficiency in this range of γ. New developments in high granular pixel detectors allow one to perform simultaneous measurements of the energies and the emission angles of generated transition radiation (TR) X-rays and use the maximum available information to identify particles. First results of studies of TR energy-angular distributions using gallium arsenide (GaAs) sensors bonded to Timepix3 chips are presented. The results are compared with those obtained using a silicon (Si) sensor of the same thickness of 500 μm. The analysis techniques used for these experiments are discussed.
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.
Silicon detectors generally satisfy the requirements of the modern physics experiments, however, experimental physics develops in the direction of increasing radiation loads, wich leads to increase ...in the requirements for radiation hardness of detectors. For other applications, such as registration of high energy X-rays, using detectors with high atomic number is important. The interest in using high resistive chromium-compensated GaAs (GaAs:Cr) in high-energy physics and other applied fields is steadily growing. This article presents a comparative study of the radiation resistance of sensors based on GaAs:Cr and Si, irradiated by 21 MeV electrons generated by the LINAC-200 accelerator. The target sensors were irradiated with the dose up to 1.5 MGy. I-V characteristics, resistivity, charge collection efficiency (CCE) and their dependences on the bias voltage and temperature were measured at different absorbed doses.
In the recent years, the method of single photon counting X-ray mu-CT is being actively developed and applied in various fields. Results of our studies carried out using the MARS mu-CT scanner ...equipped with GaAs Medipix-based camera are presented. The procedure of mechanical alignment of the scanner is described, including direct and indirect measurements of the spatial resolution. The software chain for data processing and reconstruction has been developed and reported. We demonstrate the possibility to apply the scanner for research in geology and medicine and provide demo images of geological samples (chrome spinellids, titanium magnetite ore) and medical samples (atherosclerotic plaque, abdominal aortic aneurysm). The first results of multi-energy scans using GaAs:Cr-based camera are shown.
A compact and finely grained sandwich calorimeter is designed to instrument the very forward region of a detector at a future e super(+)e super(-) collider. The calorimeter will be exposed to low ...energy e super(+)e super(-) pairs originating from beamstrahlung, resulting in absorbed doses of about one MGy per year. GaAs pad sensors interleaved with tungsten absorber plates are considered as an option for this calorimeter. Several Cr-doped GaAs sensor prototypes were produced and irradiated with 8.5-10MeV electrons up to a dose of 1.5MGy. The sensor performance was measured as a function of the absorbed dose.
High resistivity gallium arsenide compensated by chromium fabricated by Tomsk State University has demonstrated a good suitability as a sensor material for hybrid pixel detectors used in X-ray ...imaging systems with photon energies up to 60 keV. The material is available with a thickness up to 1 mm and due to its Z number a high absorption efficiency in this energy region is provided. However, the performance of thick GaAs:Cr-based detectors in spectroscopic applications is limited by readout electronics with relatively small pixels due to the charge sharing effect. In this paper, we present the experimental investigation of the charge sharing effect contribution in the GaAs:Cr-based Timepix detector. By means of scanning the detector with a pencil photon beam generated by the synchrotron facility, the geometrical mapping of pixel sensitivity is obtained, as well as the energy resolution of a single pixel. The experimental results are supported by numerical simulations. The observed limitation of the GaAs:Cr-based Timepix detector for the high flux X-ray imaging is discussed.
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.
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