Possibility of generation of octavalent curium in the gas phase in the form of volatile tetraoxide CmO4

Experiments based on gas thermochromatography were performed with the aim to search for volatile tetraoxide CmO₄ in the products of thermal oxidation of microamounts of CmH_2–3. The carrier gas was He, and the reagent gas was O₂. At their equimolar ratio, the zone of deposition of volatile Cm species at negative temperatures, centered at ?80°C, was detected on the quartz column surface. The thermochromatographic peaks formed by plutonium tetraoxide and by the volatile Cm species are similar in shape. The enthalpy of adsorption of this species on the quartz surface was calculated to be ?47 ± 12 kJ mol^?1. The data obtained are compared to the results of previous experiments with PuH_2–3. The chemical behavior of the volatile Cm species at decreased O₂ concentration in the carrier gas (1 and 5%) was studied. It resembles the previously studied behavior of PuO₄ under similar conditions. It was concluded that the volatile Cm species has the formula CmO₄.     

The viscosity and self-diffusion of rarefied steam: Refinement of reference data

New experimental data on the viscosity of rarefied stem [1] confirm the prediction potentialities of the calculations of steam properties using the modified m-6-3 Stockmayer potential. Repeated processing is performed of experimental data on the viscosity and self-diffusion coefficient of steam in the temperature range from 280 to 1400 K, and refined tables of reference data for the properties under consideration are calculated.     

Effect of fuel/oxidizer ratio and the calcination temperature on the preparation of microporous-nanostructured tricobalt tetraoxide

Microporous tricobalt tetraoxide, Co₃O₄, nanoparticles (NPs) clusters have been successfully fabricated using a simple but efficient controlled solution combustion route. Such a synthesis involves combustion reaction of cobalt nitrate with cetyl trimethylammonium bromide (CTAB). The combustion process has been analyzed by simultaneous thermal analysis. The resultant powders were characterized by means of X-ray diffraction technique (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and nitrogen adsorption at −196 °C. The morphology and specific surface area of the obtained Co₃O₄ nanoparticles clusters have proved to be strongly dependent on the fuel (F)/oxidizer (O) molar ratio and the calcination temperature. It was found that both the crystallite size and the lattice parameter nanocrystalline Co₃O₄ increase with increasing the F/O molar ratio as well as the calcination temperature. X-ray diffraction confirmed the formation of CoO phase together with spinel Co₃O₄ using F/O ratio of 1. The concentration of such phase increases with increasing the F/O ratio. Moreover, when the calcination is applied at 900–1000 °C traces of CoO was obtained together with Co₃O₄ as a major phase.     

Radiation-Chemical Behavior of Plutonium in the Heterogeneous System PuO2-Ground Water

Radiation-chemical behavior of plutonium in the heterogeneous system PuO₂-ground water from the Red forest in the vicinity of Chernobyl NPP was studied. It was found that, in nonirradiated and irradiated ground water, Pu(IV) passes into the aqueous phase with subsequent transformation into Pu(V) and Pu(III). The degree of plutonium leaching is governed by the amount of organic substances, particularly fulvic and mellitic acids, in the ground water, and the degree of conversion of Pu(IV) to Pu(III) and Pu(V), by the ionizing radiation dose. The physicochemical and radiation-chemical behavior of plutonium in the systems was judged from the spectral characteristics of the irradiated and nonirradiated solutions.     

A Mathematical Model of Radiolysis of Water Sorbed on PuO2

A mathematical model of radiolysis of water sorbed on PuO₂ was developed. The model is basedon the postulate that the kinetic characteristics of formation of the initial products in -radiolysis of sorbedwater (H₂, O₂, H₂O, e^- _{e q}, OH) depend on its content. To explain experimental data showing that the steady-state amounts of H₂ are practically equal to the initial amount of sorbed water, the reaction betweenPuO₂ and H₂O₂ yielding H₂O and superstoichiometric plutonium dioxide was postulated. The minimum value of the rate constant of this reaction was found (2 ×10^{- 3} mol^{- 1} s^{- 1}). The proposed mathematical model adequately describes the experimental data on formation of hydrogen and oxygen released from water in contact with PuO₂ at its prolonged storage.     

Use of air monitoring and experimental aerosol data for intake assessment for Mayak plutonium workers

One of the major uncertainties in reconstructing doses to Mayak Plutonium (Pu) workers is the unknown exposure patterns experienced by individuals. These uncertainties include the amounts of Pu inhaled, the temporal exposure pattern of Pu air concentration, the particle-size distribution and solubility of the inhaled aerosols. To date, little individual and workplace-specific information has been used to assess these parameters for the Mayak workforce. However, extensive workplace-specific alpha activity air monitoring data set has been collated, which, if coupled with individual occupational histories, can potentially provide customised intake scenarios for individual Mayak workers. The most available Pu air concentration data are annual averages, which exist for over 100 defined work stations at radiochemical and chemical-metallurgical manufacturing facilities and basically for the whole period of Mayak production operations. Much sparser but more accurate data on Pu concentrations in workers' breathing zone are available for some major workplaces and occupations. The latter demonstrate that within a working shift, Pu concentrations varied over a range of several orders of magnitude depending on the nature of the operations performed. An approach to use the collated data set for individual intake reconstruction is formulated and its practical application is demonstrated. Initial results of ongoing experimental study on historic particle size at Mayak PA and their implications for intake estimation are presented.     

Physicochemical characteristics and radiation-chemical processes in the system PuO2-sorbed water

The experimental data on formation of H₂ and O₂ during storage of PuO₂ samples containing sorbed water were analyzed. It was shown that the rates of formation of these gases, all other factors being the same, are governed by the procedure of water sorption: in sorption from the liquid phase these rates are significantly higher than those in sorption from the gas phase. To elucidate the conditions of safe storage of PuO₂, it is necessary to obtain systematic quantitative data on the kinetics of H₂ and O₂ formation in the system consisting of PuO₂ and water sorbed from moist air. The optimized mathematical model of sorbed water radiolysis adequately describing the experimental data on the formation of H₂ and O₂ at room temperature in the system consisting of PuO₂ and water sorbed from the liquid phase is presented. The rate constant of H₂ and O₂ recombination in the presence of PuO₂ containing 2–3% water was found to be ≤ 1 × 10^?5 mol^?1 s^?1. With the knowledge of the reaction rate constants, the model allows calculation of the amounts of H₂ and O₂ and the pressure in the storage vessel depending on the amount of sorbed water, radiation dose rate, and storage duration.     

Refinement on the theoretical analysis of multifiber ceramic capacitor

In a previous paper, a new type of ceramic capacitor, multifiber ceramic capacitor (MFC), was designed and analyzed to compare the properties with multilayer ceramic capacitors (MLC). Refinement on the theoretical analysis of the MFC is presented in this paper for the capacitors made from dielectric film less than 2 m thick. A critical _c exists above which the specific capacitance of an MFC is higher than an MLC, where is the ratio of the dielectric thickness of the MLC and the MFC. Such a _c value is readily attainable because a high-quality dielectric coating on fiber substrates can be easily produced by modern thin-film technology. In other words, MFC has the potential to surpass MLC in term of the specific capacitance. Core fibers (inner electrodes) with a small diameter should be selected, whenever possible, for improved specific capacitance. The choice of possible materials for the MFC is also discussed.     

Refinement of the 225Ac half-life

Precision measurements were made to determine the ²²⁵Ac half-life. The ²²⁵Ac loss in the samples was monitored using β- and γ-ray spectrometry by the activity of daughter decay products occurring in radioactive equilibrium with the parent radionuclide. The ²²⁵Ac half-life is 9.912 ± 0.003 days. The result obtained was compared with the published data.     

Thermal conductivity of nitrogen at high pressures and atmospheric pressure: Refinement of generalized data

The paper analyzes possible causes of discrepancies in the generalized literature data on thermal conductivity of nitrogen for P=0.1 MPa and T ≥300 K. The data are refined with the aid of a temperature power dependence in the region of 300 – 2500 K.     

Formation of H2 and O2 in Radiolysis of Water Sorbed on PuO2

Samples of PuO₂ containing sorbed water, when stored at room temperature, release hydrogen and oxygen into the gas phase. At a given content of water, the rates of formation of H₂ and O₂ are in direct proportion to the dose rate of plutonium radiation. With increasing concentration of water from 0.3 to 3% the rates of formation of H₂ and O₂ increase by a factor of 60-100, which is caused by increase in both the energy of -radiation absorbed by water and radiation-chemical yields of formation of H₂ and O₂. The radiation-chemical yields of formation of oxygen and hydrogen at the 0.3% content of sorbed water are lower, and at the water content exceeding 1%, higher than the yields of these products in radiolysis of free water. On storage of powder-like and pelletized samples of PuO₂ of power reactor origin with a 3% water content for 150-200 days, the stationary concentration of hydrogen approximately corresponding to the initial concentration of sorbed water is established.     

The form of the stress tensor for superfluid4He

From an approach based on reduced density matrices it follows that the stress tensor for a superfluid contains a quite new off-diagonal term occurring also in the entropy equation. Examination of this problem on the basis of the theory proposed by Bogoliubov suggests that the new term should be added to the static pressure to give the total pressure. In addition, it is demonstrated that the second derivative of free energy with respect to volume and the square of the superfluid velocity do not commute.     

Distribution of plutonium particles in the lungs of Mayak workers

Lung tissues from workers at the Mayak Production Association were examined to determine the distribution of plutonium (Pu) activity in various lung compartments. Stereological sampling methods and autoradiography were used. Pu particles were identified by microscopic examination of autoradiographs and localised in one of six normal anatomic sites and two sites of fibrosis (parenchymal, non-parenchymal). Particle activity was determined by counting the number of tracks emanating from the particles. Over 50% of the Pu activity was localised in sites of fibrosis, which had significantly higher than average activity for the lung. Over 40% of the activity was in lung parenchyma. Activity in the bronchovascular interstitium was significantly lower than average. These results support the hypothesis that Pu activity is not uniformly distributed in the lung, with long-term retained particles concentrated in scars of the lung. The results may significantly affect estimates of dose from inhaled Pu.     

Certification of the reference sample of plutonium dioxide

An algorithm of certification of plutonium dioxide by the coulometric method is described. The results of measuring the mass fraction of Pu in PuO₂, obtained in certifying and confirming measurements in the course of the development of the state standard sample, are given. The mean mass fraction of Pu in the standard sample material and the uncertainty of the certified value are determined. Based on the results obtained and metrological expertise of the documentation in accordance with GOST (State Standard) 8.315–97, the type of plutonium dioxide composition, SS Pl-tot, is approved, included into the state register, and accepted for use in the Russian Federation.     

Sensitivity analysis of the urinary excretion of plutonium

The transfer parameters of a new age-related model for plutonium metabolism, which have the largest influence on urinary excretion, are determined by applying a sensitivity analysis and assuming a direct uptake into blood. Realistic cases of contamination via ingestion and inhalation were considered as well and sensitivity coefficients for non-systemic parameters were calculated. The most important parameters in relation to the path of intake are identified and the effects of the modifying factors proposed by the ICRP in the case of alteration of respiratory tract physiology are briefly examined.