Radiochemistry最新文献

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 spark plasma sintering. Submicron phosphate powders with particle sizes less than 1 μm were produced 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 influence of the contact environment on the rate and mechanism of Sr leaching from Sr_0.5Zr₂(PO₄)₃ ceramic samples within 42 days was investigated. It was shown that over testing in distilled water and in mineral water (up to 7 days) Sr leaching occurs due to the dissolution of the surface layer of ceramics and after 7 days of testing in mineral water, due to washing out of Sr from the open ceramic surface.

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 financial 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 fields of Azerbaijan are adduced. The studies were carried out under the influence 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 influence 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 the estimation of the potential of the radiation-thermal method for producing oil products for various purposes.

The extraction of U(VI), Th(IV), Am(III), and Eu(III) with solutions of phosphorylated pyridines from nitric acid solutions has been studied. The stoichiometry of the extractable complexes was established. In terms of their extraction ability, these compounds are inferior to bis(diphenylphosphinyl)methane, but they are significantly superior to carbamoylmethylphosphine oxides. An increase in the number of phosphine oxide groups in the molecules of phosphorylated pyridines leads to a significant decrease in their extraction ability and selectivity in the extraction of Am(III) and Eu(III) from nitric acid solutions.

The review is devoted to a comparison of new experimental data on the sublimation of uranium–zirconium carbonitrides with different contents of carbon, nitrogen, and oxygen impurities at high temperatures (1700–2300 K), we obtained in the past 2 years, with data of previous reported works on the sublimation of uranium carbonitrides, we and other authors prepared 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 essential 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 bring about 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.

Analysis of available monitoring data sets on concentrations of accidentally derived dissolved radiocesium in water bodies is indicative of two major physicochemical mechanisms responsible for their seasonal variations in water bodies in the course of the year: temperature dependence of radiocesium desorption from suspended material and ion-exchange remobilization of radiocesium by ammonium cations formed during decomposition of organic matter in anoxic conditions. An equation describing seasonal variations in concentration of dissolved radiocesium in water bodies has been derived accounting for two factors: water temperature, and combined concentration of key competing cations.

Oxidation of UO₂ and UN by atmospheric oxygen and nitrogen hemioxide, which is a hard-to-localize greenhouse gas, was investigated by thermal analysis. For oxidation, mixtures of N₂O–N₂ and O₂–N₂ were used with a 20% volume fraction of the oxidizing agent. For UO₂ and UN, the phase composition of the final oxidation product in air and in N₂O is the same―U₃O₈. In both cases, N₂O behaves as a milder oxidizing agent compared to atmospheric oxygen. Oxidation of UO₂ and UN in an N₂O flow starts at a temperature 180 and 70°C higher than in air, respectively. The oxidation of UN in an N₂O flow proceeds in three stages. At the first stage, the reaction products are UO₂ and U₂N₃; UO₂ is the product of the second stage; and at the third stage U₃O₈ is produced. No pronounced staging is observed in the UO₂ oxidation process. The possibility of utilizing nitrogen hemioxide when it is used in the course of voloxidation (oxidation) of spent nuclear fuel is shown.

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 studied. 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 was shown that, depending on the pH of the solution, the main equilibrium phases with the solution are phases 4 and 5. X-ray diffraction analysis, Raman spectroscopy, and ³¹P NMR data of the phase (1) samples after contact with a solution of 0.01 M 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, correspond to the presence of surface phases 4 or 5. The model of surface complexation in the Henry region adequately describes the mechanism of Sr(II) sorption by the surface phase 5 on TCP particles in the form of the SrHPO₄⁰ complex. The formation of the HA complex of Sr(II) in solution does not affect distribution coefficient K_d(Sr) in the range of HA concentrations of 0–150 mg/L due to the competitive effect of hydrogen phosphate ions on strontium complexes.

The radiation thermal stability of extraction mixtures based on methyltrioctylammonium (MTOA) carbonate was studied. The volumes and maximum rate of release of gaseous products at atmospheric and elevated pressures were determined. No exothermic processes were shown to occur in the studied mixtures under experimental conditions. Irradiation up to a dose of 1 MGy has little effect on the density, viscosity, and surface tension of mixtures, but significantly reduces the phase separation rate. The distribution coefficients of Am(III) in the system of 50% MTOA carbonate in toluene are practically independent of the absorbed dose; however, irradiation can significantly affect the composition of the extractable americium complexes. The results of the study of extraction systems showed their high radiation thermal stability.