Determining the Instantaneous Effective Energy of x-Ray Tube Bremsstrahlung

A method is described for determining the instantaneous effective energy of x-ray tube brehmsstrahlung by means of two semiconductor detectors employing epitaxial GaAs structures and a measurement circuit, which together determine the effective energy with an error of 5% in the range 20–80 keV in the presence of nonlinearity in the detector response.     

1D GaAs Detector Arrays for Digital X-ray Imaging with a 108-μm Spatial Resolution

A 1D x-ray detector array of pitch 108 m is designed, fabricated, and tested. The array is based on the p⁺–n–n–n⁺ structure made in epitaxial GaAs technology. Guard rings are incorporated to reduce detector cross coupling. It is announced that the technology proposed will be used to make arrays with a pitch of 50 m and a spatial resolution of 10 line-pairs/mm, suitable for digital mammography.     

1D GaAs Detector Arrays for Digital X-ray Imaging

1D imaging arrays of GaAs x-ray detectors are designed, fabricated, and tested. Each array consists of 64 detectors arranged with a pitch of 0.4 mm. In x-ray testing, an almost linear relationship is found between the detector response and the tube current. Zero detector cross coupling is observed in scanning an x-ray beam along any array.     

Photovoltaic X-ray detectors based on epitaxial GaAs structures

A new type of the photovoltaic X-ray detector based on epitaxial p ⁺-n-n′-n ⁺ GaAs structures is proposed, which provides for a high efficiency of charge carrier collection in a nonbiased operation regime at room temperature. The GaAs structures were grown by vapor phase epitaxy on heavily doped n ⁺-GaAs substrates. The X-ray sensitivity range covers the effective energies from 8 to 120 keV. The maximum output signal in the short-circuit regime is 30 μA min/(Gy cm²). The detector response to γ-radiation from a ¹³⁷Cs[660 keV] radioactive isotope was measured.     

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.     

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.     

Deposition of CeO2 films including areas with the different orientation and sharp border between them

Epitaxial films from one material, with sharp borders between contacting regions having different film orientation are grown on one surface of the substrate for the first time. The main reason for the deposition of thin ceria layers with mixed (001) and (111) orientations on a (1 02) sapphire substrate is determined. We suggest that this is related to the availability of surface defects which, in thin near-surface layers, deviate from stoichiometric composition. This in turn is connected with the loss of oxygen.

A technique for influencing CeO₂ film orientation is demonstrated. This involves specific preliminary processing of the substrate, and the selection of oxygen partial pressure during the deposition process.

High quality thin (30–50 nm) “protective” (001) CeO₂ epitaxial layers are prepared on (1 02) Al₂O₃. Structures comprising two epitaxial protective CeO₂ layers, orientations (001) and (111), are made on the base of (0001) and (1 02) sapphire substrates. The interface between the epitaxial layers is <1 000 nm.

Preliminary results using this method are described, and the possibility of creating a “bi-epitaxial” transition in thin YBa₂Cu₃O_7−x layers is explored.