Theoretical and Mathematical Physics ,
Dynamical Systems and Chaos ,
Material Sciences ,
Radiation Instruments and Radiography ,
Scintillators and Detectors
Publications (5)
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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.
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.
Multi-energy radiography is a new direction in non-destructive testing. Its specific feature is separate detection of penetrating radiation in several energy channels. Multi-energy radiography allows quantitative determination of the atomic composition of objects. This is its principal advantage over conventional radiography. In particular, dual-energy radiography allows determination of the effective atomic number of a material with an accuracy of up to 80-90%. Development of three-energy radiography and radiography of higher multiplicity makes it possible to further improve the reconstruction of an object's chemical composition. This presents the possibility, for example, of detection of explosives and other illegal objects in luggage with a reliability approaching 95-98%. These developments can find application not only in anti-terrorist activities, but also in industrial testing and nuclear medicine.
Intrinsic resolution of the scintillator is one of the most important constituents of the full energy resolution of a detector. Intrinsic resolution contains components preserved at any ionizing radiation energy. A major role is played by the resolution of light collection. This is a component determined by geometric-optical non-uniformities of scintillation energy propagation and collection. In this work, theoretical studies of general light collection features have been carried out. A universal law has been predicted for light collection dispersion in detectors of regular beam dynamics. Such systems include scintillation blocks with mirror reflecting surface and regular geometry in the shape of cylinder, parallelepiped or sphere. An important regular collection feature is weak dependence of its dispersion on the scintillator material or shape. This allows to relate spectrometric efficiency and detection efficiency for any detector of the said type. The theoretically obtained law is confirmed by the available experimental data. The developed theory allows finding new ways to eliminate internal noises affecting the radiation measurements data. Such optimization is a necessary condition for creation of new detectors with improved characteristics.
The development prospects of a scintillator-photodiode type detector with an improved energy resolution attaining few per cent, about 1.5 to 2.5%, are considered. The main resolution components have been analyzed theoretically, their theoretical and physical limits have been established. Empirical data on the properties of novel scintillators have been considered confirming the possibility of the energy resolution improvement. Ways have been proposed to optimize the detector statistical fluctuations and the scintillator intrinsic resolution. A specific importance of the intrinsic resolution is shown as a limiting threshold factor at the ionizing radiation energy values from 662 keV to 10 MeV and over.
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