Oleksandr D. Opolonin

The neutron detectors based on oxide scintillators for control of fissionable radioactive substances

A large-area X-ray CMOS image sensor (LXCIS) is widely used in mammography, non-destructive inspection, and animal CT. For LXCIS, in spite of weakness such as low spatial and energy resolution, a Indirect method using scintillator like CsI(Tl) or Gd2O2S is still well-used because of low cost and easy manufacture. A photo-diode for X-ray imaging has large area about 50 ~ 200 um as compared with vision image sensors. That is because X-ray has feature of straight and very small light emission of a scintillator. Moreover, notwithstanding several structure like columnar, the scintillator still emit a diffusible light. This diffusible light from scintillator can make spatial crosstalk in X-ray photodiode array because of a large incidence angle. Moreover, comparing with vision image sensors, X-ray sensor doesn’t have micro lens for gathering the photons to photo-diode. In this study, we simulated the affection of spatial crosstalk in X-ray sensor by comparing optical sensor. Additionally, the chip, which was fabricated in 0.18 um 1P5M process by Hynix in Korea, was tested to know the effect of spatial crosstalk by changing design parameters. From these works, we found out that spatial crosstalk is affected by pixel pitch, incident angle of photons, and micro lens on each pixels.

Capabilities of dual-energy x-ray imaging in medicine and security

The dual-energy computer tomography compared with its traditional single-energy variant ensures substantially higher contrast sensitivity. The evaluation of the signal ratio from high-energy and low-energy detectors has been carried out using a simplified model of the dual-energy detector array and accounting for the X-ray tube spectrum. We proposed to use of a dual-energy receiving–detecting circuit with a detector pair ZnSe/CsI or ZnSe/CdWO that allows efficient distinction between muscular and bone tissues, which supports our earlier theoretical assumptions that this method could be successfully used for separate detection of materials differing in their effective atomic number Zeff and local density (e.g., calcium contents in bone densitometry), so as can be turn to account for new generation instruments. A possibility of dual energy tomography use for osteoporosis diagnostics was considered. Direct image reconstruction of biological objects has been carried out, demonstrating details of bones with different density. The density of the bone depends on the calcium content, which is not more than 20 % for the narrow part and about 18,5 % in the broad part. This results obtained were in good agreement with the results of the independent chemical analysis.

Professional and household dosimeters for UV biologically active ranges of solar radiation on the basis of ZnSe semiconductor-metal nanostructures

Development is reported of a small-sized ultraviolet (UV) radiometer designed for measurements of energy characteristics of UV radiation - energy illuminance and energy exposure. Main characteristics are considered of nZnSe(O, Te)/Ni Schottky structures created for the developed UV radiometer and used as UV sensors. Characteristics are presented of optical glass filters and interference light filters designed for separation of different biologically relevant UV spectral regions.

Development of receiving-detecting circuit for digital radiographic systems with improved spatial resolution

Detection of X-ray radiation by digital radiographic systems (DRS) is realized using multi-element detector arrays of scintillator-photodiode (S-PD) type. Accounting for our experience in development of X-ray introscopy systems, possibilities can be found for improvement of DRS detection efficiency. Namely, a more efficient use of the dynamic range of the analog-to-digit converter by means of instrumental compensation of scatter of detector characteristics and smaller apertures of individual detection channels. However, smaller apertures lead to lower levels of useful signals, and a problem emerges of signal interference over neighboring channels, which is related to optical separation of the scintillation elements. Also, more compact arrangement of electronic components of preamplifiers is achieved. The latter problem is solved by using multi-channel (from 32 to 1024 channels) photoreceiving devices (PRD). PRD has a set of photosensitive elements formed on one crystal, as well as shift registers ensuring preliminary amplification of signals and series connection to one outlet. The work envisages creation of receiving-detecting circuit (RDC) with improved spatial resolution (ISR) with the aim of producing advanced DRS with improved characteristics: density resolution better than 0.9%, and detecting ability allowing detection of θ 0.5 mm steel wire behind 6 mm steel. The work will result in the development of RDC with ISR (800-200 microns). In combination with various ionizing radiation sources and scanning mechanisms this will allow creation of DRS for many tasks of non-destructive testing (NDT) and technical diagnostics (TD), in particular, for check-up of pipelines, objects of oil and gas industries, etc. This work was supported by the Ministry of Education and Science of Ukraine, the U.S. Civilian Research and Development Foundation (CRDF), and by the NATO Science for Peace and Security Program (Project SfP-982823).

Multi-energy method of digital radiography for imaging of biological objects

This work has been dedicated to the search for a new possibility to use multi-energy digital radiography (MER) for medical applications. Our work has included both theoretical and experimental investigations of 2-energy (2E) and 3- energy (3Е) radiography for imaging the structure of biological objects. Using special simulation methods and digital analysis based on the X-ray interaction energy dependence for each element of importance to medical applications in the X-ray range of energy up to 150 keV, we have implemented a quasi-linear approximation for the energy dependence of the X-ray linear mass absorption coefficient μm (E) that permits us to determine the intrinsic structure of the biological objects. Our measurements utilize multiple X-ray tube voltages (50, 100, and 150 kV) with Al and Cu filters of different thicknesses to achieve 3-energy X-ray examination of objects. By doing so, we are able to achieve significantly improved imaging quality of the structure of the subject biological objects. To reconstruct and visualize the final images, we use both two-dimensional (2D) and three-dimensional (3D) palettes of identification. The result is a 2E and/or 3E representation of the object with color coding of each pixel according to the data outputs. Following the experimental measurements and post-processing, we produce a 3Е image of the biological object – in the case of our trials, fragments or parts of chicken and turkey.

A dual-energy medical instrument for measurement of x-ray source voltage and dose rate

An original dual-energy detector and medical instrument have been developed to measure the output voltages and dose rates of X-ray sources. Theoretical and experimental studies were carried out to characterize the parameters of a new scintillator-photodiode sandwich-detector based on specially-prepared zinc selenide crystals in which the low-energy detector (LED) works both as the detector of the low-energy radiation and as an absorption filter allowing the highenergy fraction of the radiation to pass through to the high-energy detector (HED). The use of the LED as a low-energy filter in combination with a separate HED opens broad possibilities for such sandwich structures. In particular, it becomes possible to analyze and process the sum, difference and ratio of signals coming from these detectors, ensuring a broad (up to 106) measurement range of X-ray intensity from the source and a leveling of the energy dependence. We have chosen an optimum design of the detector and the geometry of the component LED and HED parts that allow energy-dependence leveling to within specified limits. The deviation in energy dependence of the detector does not exceed about 5% in the energy range from 30 to 120 keV. The developed detector and instrument allow contactless measurement of the anode voltage of an X-ray emitter from 40 to 140 kV with an error no greater than 3%. The dose rate measurement range is from 1 to 200 R/min. An original medical instrument has passed clinical testing and was recommended for use in medical institutions for X-ray diagnostics.

Three-energy radiography method for uniformity control of composite materials including components with different effective atomic numbers

Presently, most X-ray security systems for luggage inspection use dual-energy detector. A drawback of this approach is that overlap in energy sensitivity of the low- and high-energy detectors creates the potential for ambiguity and inaccuracy. We have made an attempt to improve the identification quality of organic materials using a three-energy receiving–detecting circuit. New model calculations and several new algorithms for the detection of organic and nonorganic materials under multi-energy radiography were proposed, developed and experimentally verified. The purpose of the present work is study of the possibility of separation between substances with small effective atomic numbers for increasing the detection probability of explosives. Using a spectrum of the X-ray tube with a tungsten anode, evaluation has been carried out of the signal ratio from high-energy detector, medium-energy detector and low-energy detectors. Using differential energy sensitivity of detectors of different thickness, varying X-ray source anode voltages and filter for each array, special software it is possible to reconstruct images of the inspected object at the different energy scales. It was shown that using standard X-ray beams and specially-chosen scintillator types with different thicknesses, we can achieve accuracy in determination of Zeff up to 95%, that significantly better as compared with systems based on conventional X-ray inspection. Using two-coordinate identification palette, one can discern between imitators of explosives even when the difference in their Zeff values is small (from 7.08 to 8.07).

X-ray radiation detectors of “scintillator-photodiode” type for security and nondestructive testing

The dual-energy computer tomography compared with its traditional single-energy variant ensures substantially higher contrast sensitivity. The evaluation of the signal ratio from low-energy and high-energy detectors has been carried out using a simplified model of the dual-energy detector array and accounting for the X-ray tube spectrum. We proposed to use of a dual-energy receiving-detecting circuit with a detector pair ZnSe/CsI or ZnSe/CdWO that allows efficient distinction between muscular and bone tissues, which supports our earlier theoretical assumptions that this method could be successfully used for separate detection of materials differing in their effective atomic number Zeff and local density (e.g., calcium contents in bone densitometry), so as can be turn to account for new generation instruments. A possibility of dual energy tomography use for osteoporosis diagnostics was considered. Direct image reconstruction of biological objects has been carried out, demonstrating details of bones with different density. The density of the bone depends on the calcium content, which is not more than 20 % for the narrow part and about 18,5 % in the broad part. This results obtained were in good agreement with the results of the independent chemical analysis.