Radiohimiâ

The review is devoted to a comparison of new experimental data on the sublimation of uranium-zirconium carbonitrides with di erent contents of carbon, nitrogen, and oxygen impurities at high temperatures (1700- 2300 K), obtained by us in the past 2 years, with data of previous works presented in the literature on the sublimation of uranium carbonitrides, obtained by us and by other authors using mass spectrometry and some other methods of thermodynamic analysis. The main attention is paid to the consideration of the composition of the gas phase and the analytical dependences of the partial pressures of its components on temperature, as well as the chemical mechanism and heats of sublimation. The main feature of the sublimation process of all materials based on uranium carbonitride (both pure and doped with zirconium) is its incongruent nature, due to the loss of nitrogen, which leads to a shift in their compositions towards the phase with higher carbon content. The chemical mechanisms of sublimation of carbonitrides of both types are considered, according to which oxygen impurities in these materials lead to the appearance of oxide components UO, UO₂ and CO in the gas phase and additional release of nitrogen. The introduction of zirconium into uranium carbonitride and an increase in the carbon content in it lead to a decrease in the partial pressures of uranium monoxide and nitrogen, which increases the thermal stability of this innovative fuel material.

Samples of ceramics based on Sr_0.5Zr₂(PO₄)₃ phosphate with the structure of the kosnarite mineral (NaZr₂(PO₄)₃, NZP) were obtained by electric pulse plasma sintering. Submicron phosphate powders with particle sizes less than 1 μm were obtained by the sol-gel method. Powders and ceramics have a single-phase NZP structure. The relative density of the ceramics was 97.6%. The chemical stability of the obtained ceramics was studied in static mode at 90°C in distilled and mineral water and in acidic and alkaline environments. The minimum achieved leaching rates were ~10^-4-10^-6 g/(cm² day). The in uence of the contact environment on the rate and mechanism of Sr leaching from Sr_0.5Zr₂(PO₄)₃ ceramic samples within 42 days was studied. It has been shown that Sr leaching occurs due to the dissolution of the surface layer of ceramics when tested in distilled water and in mineral water (up to 7 days) and due to Sr leaching from the open ceramic surface after 7 days of testing in mineral water.

The extraction of U(VI), Th(IV), Am(III), and lanthanides(III) from nitric acid solutions with solutions of phosphorylated pyrazines in organic solvents has been studied. The stoichiometry of the extracted complexes was determined, and the in uence of the structure of the extractant and the concentration of HNO₃ in the aqueous phase on the e ciency of the extraction of metal ions into the organic phase was considered. It has been established thatm among the studied compounds, bis(diphenylphosphine)quinoxaline dioxide has the highest extraction ability with respect to actinides and lanthanides in nitric acid media.

The sorption behavior of traces Sr(II) toward β-Ca₃(PO₄)₂ (TCP) depending on the concentration of the cation, pH, and concentrations of humic acids (HA) in the solution was udied. Thermodynamic analysis of the solubility of TCP (1) was performed taking into account the formation of Ca(OH)₂ (CH, 2), Ca(H₂PO₄)₂ (MCPA, 3), CaHPO₄·2H₂O (DCPD, 4), Ca₅(PO₄)₃OH (hydroxyapatite, OHAp, 5), and Ca₂P₂O₇ (DCPP, 6). It is shown that, depending on the pH of the solution, the main equilibrium phases with the solution are phases (4) and (5). X-ray di raction analysis, Raman spectroscopy, and ³¹P NMR data of the phase (1) samples after contact with a solution of 0.01 mol/L NaNO₃ for about 10 days showed the presence of only the phase (1). The solubility of (1) regarding the concentration of Ca²⁺, PO₄^3- ions and the stoichiometric ratio (Ca/P) in solutions, depending on pH, corresponds to the presence of surface phases (4) or (5). The model of surface complexation in the Henry region adequately describes the mechanism of sorption of Sr(II) by the surface phase (5) on TCP particles in the form of the SrHPO₄⁰ complex. The formation of the HA complex Sr(II) in solution does not a ect distribution coe cient K _d(Sr) in the range of HA concentrations of 0-150 mg/L due to the competitive e ect of hydrogen phosphate ions on strontium complexes.

An automated module for the synthesis of L-[¹¹C-methyl]methionine, a well-known PET radiotracer for brain tumor imaging, has been designed. The module meets modern requirements for the production of radiopharmaceuticals and radiation safety; thanks to the original program created in the Delphi programming environment, module is convenient for the synthesis control (user-friendly) and operation; the service can be maintained on its own with minimal time and nancial costs. The module ensures the production of L-[¹¹C-methyl]methionine with high chemical, radiochemical and enantiomeric purity and a radiochemical yield of 30% (based on [¹¹C]CO₂ activity, not decay corrected).

The results of study of gas formation at the radiation-thermal transformation of bituminous rocks of Kirmaku elds of Azerbaijan are adduced. The studies were carried out under the in uence of γ-radiation and accelerated electrons in a wide range of temperatures (20-500°C), absorbed dose (0-260 kGy), and dose rate (1 and 470 Gy/s).The in uence of temperature and adsorbed dose on the gas formation rate and content of products has been established. Estimates of technical and economic indicators of the process are given The results of these studies allow us to estimate the potential of the radiation-thermal method for producing oil products for various purposes.