A. G. Petrov

Calculation of the atomic scattering factors of fast electrons at zero angle of incidence of an electron beam and mean inner crystal potentials

The atomic scattering factors of fast electrons at zero angle of incidence of an electron beam, fel(0), are calculated for neutral atoms with Z = 1−54, using the mean-square radii of electron-density distributions in atoms and ions, derived on the basis of the Hartree-Fock wave functions. The values of fel(0) have been calculated for the first time for some positive and negative ions. The obtained values of fel(0) were used to determine the mean inner potentials V0 of metallic, covalent, and ionic crystals. The calculated values of V0 are compared with the experimental data in the literature. The values of V0 calculated for III–V and II–VI compounds are reported.

Performance of Cd0.9Zn0.1Te X-ray detectors versus the purity of initial components

X-ray detectors made of Cd0.9Zn0.1Te single crystals are studied. Starting components (Cd, Zn, Te) are obtained by multistage volume distillation. Synthesized CdZnTe is finally purified by continuous vacuum sublimation. Detectors highly sensitive to X rays are produced.

X-ray sensitivity of Cd0.9Zn0.1Te detectors

The X-ray sensitivity of Cd0.9Zn0.1Te detectors as a function of the effective X-ray energy and bias voltage is studied. It is shown that the sensitivity grows with effective X-ray energy and much more significantly with bias voltage. The sensitivity depends on the angle the X-ray beam makes with an electric field in the detector. In the energy range 28–72 keV, the sensitivity is the highest when the X-ray beam is normal to the electric field in the detector.

Photovoltaic X-ray detectors on the basis of GaAs epitaxial structures

The results of investigations of the properties of a new photovoltaic X-ray detector are presented. The detector was manufactured on the basis of a GaAs (p+-n-n′-n+) epitaxial structure, which was grown using the vapor-phase epitaxy method. The detector sensitivity to X-rays in a range of effective energies of 7–120 keV was measured. Multichannel linear X-ray detectors were developed and used in obtaining high-quality digital images.

Photovoltaic GaAs Detectors for Digital X-Ray Imaging

The short coming of the conventional film-screen systems arises from limited dynamic range due to the film latitude and Swank noise from the screen and film granularity that limits the system rather than quantum fluctuations. A thin intensifying screen is used to achieve better spatial resolution; however thin screens also have limited detector quantum efficiency. Most currently available digital X-ray systems use scanned-slit geometries to minimize tehe required detector area and minimize system complexity. Scanned-slit systems achieve also efficient rejection of Compton scattered X-rays by suffering significant X-ray tube loading in comparison to conventional large-field imaging geometries. There remains a significant clinical need in production of detection systems with sufficiently high spatial resolution and detection quantum efficiency. An improvement of digital radiography compared to conventional systems is the high dynamic range. Futhermore real-time data acquisition is possible and digital image processing can be performed. A digital image representation has become feasible because of the availability of digital mass storage media.

Characteristics of a photovoltaic X-ray detector based on a GaAs epitaxial structure

The characteristics of a photovoltaic X-ray detector based on the GaAs p+-n-n′-n+ epitaxial structure grown using gas-phase epitaxy are studied. Typical current-voltage and capacitance-voltage characteristics of the epitaxial structures are analyzed together with the built-in electric field profile in the n-GaAs depleted region. The efficiency of charge accumulation in the photovoltaic detector is measured for zero bias and for a bias voltage of 17 V. It is shown that the GaAs-based photovoltaic X-ray detector can operate with zero bias voltage at room temperature. The sensitivity of the detector is measured as a function of the effective energy of X-rays and the angle of incidence of X-ray photons.

Reduction of the Output Ripple in X-Ray Detectors

In a multichannel X-ray detector based on epitaxial GaAs structures, a low-pass filter was used to reduce the ripple at the amplifier output. From the transient processes observed during the X-ray scanning, the optimum filter passband was determined. An X-ray source with a medium-frequency power-supply generator was used to estimate the image quality.

Multiple-pixel X-ray linear detector based on single CdZnTe crystals

The design of an X-ray linear detector based on single crystals Cd0.9Zn0.1Te has been described. The results of usage have been given.

X-ray detectors based on CdZnTe crystals grown from the vapor phase

X-ray detectors on the basis of vapor-phase-grown Cd0.92Zn0.08Te crystals are fabricated. The main characteristics of the detectors are investigated. It is shown that vapor-phase-grown CdZnTe crystals can be successfully used for making X-ray detectors.

Photovoltaic X-ray detectors made of CdTe crystals with a p-n junction

X-ray detectors made of CdTe crystals with a p-n junction obtained by diffusion of In into p-CdTe are investigated. The basic characteristics of such a detector are studied for the first time. It is found that the device is highly sensitive to X rays at a low bias voltage (to −50 V) and the X-ray effective energy in the range 28–72 keV. It is shown that photovoltaic detectors based on CdTe with p-n junctions are superior to Cd0.9Zn0.1Te ones.