Petya Kovacheva

Distribution of platinum group elements and other traffic related elements among different plants along some highways in Germany

Using ICP-MS and ICP-AES platinum group elements (Pt, Pd, Rh, Ru and Ir) and Ce, La, Nd, Pb and Zr have been determined in street dust, Taraxacum officinale (dandelion), Plantago lanceolata (plantain), Lolium multiflorum (annual ryegrass), Rhytidiadelphus squarrosus (moss) and Vascellum pratense (mushrooms) collected along highways and streets in Germany during 1999. Among the plants Taraxacum officinale (dandelion) reflects most adequately the pollution with the investigated elements matching the results from street dust. A strong positive correlation between all elements determined in the plants is established. Transfer factor for Pt between soil and plants has been determined in an agricultural experiment ranging between 0.004 and 0.008 for two types of soils.

Influence of freezing on physicochemical forms of natural and technogenic radionuclides in Chernozem soil

Sharp variations of different climatic parameters influence the transport, transfer, and deposition of contaminants in nature. Investigations of the impact of environmental temperature on the fractionation of radionuclides in soil are necessary for adequate assessment of their distribution and bioavailability in case of a nuclear accident. The impact of a sharp decrease of environmental temperature shortly after radioactive contamination on the physicochemical fractionation of natural and technogenic radionuclides in Chernozem soil and its influence on their potential migration ability and bioavailability in case of subsequent warming were evaluated. The soil was contaminated in a laboratory with 241Am, 60Co, 137Cs, 228Ra, 234Th, and U and two temperature regimes were used for storage. Changes of the radionuclides association with various soil phases in the first weeks after contamination were studied. Physicochemical forms of 241Am, 60Co, 228Ra, 234Th, and U were determined using two sequential extraction procedures. The ion-exchangeable forms of 137Cs were evaluated by single extraction with 1 M NH4NO3. The data showed that the freezing, following the radioisotope contamination of the soil, causes an increase of the amount of potentially mobile forms of radiocobalt, radiocesium, radium, and thorium and has an insignificant impact on the fractionation of americium and uranium.

Physicochemical fractionation of americium, thorium, and uranium in Chernozem soil after sharp temperature change and soil drought

A sequential extraction procedure was used to study the changes in the physicochemical forms of americium (Am), thorium (Th), and uranium (U) in laboratory-contaminated Chernozem soil as a result of sharp variations of the environmental temperature and soil moisture. The influence of freezing and soil drought on the radio-ecological hazard was evaluated three months after radioactive contamination with aqueous solutions of 241Am, 234Th, and U. The subsequent changes in the physicochemical forms of the actinides, caused by sharp increases in the environmental temperature and soil moisture, were examined for one month. The data showed that continuous freezing increased the potentially mobile forms of Am and Th but had the opposite effect on U. Prolonged soil drought did not influence the fractionation of Am and Th but led to the redistribution of U between the carbonates and organic matter and caused its immobilisation. The sharp increase in the temperature of the frozen soil caused the immobilisation of Am and Th and increased the potential mobility of U. The warming and enhanced humidity of the dry soil led to the immobilisation of Am and redistribution of U between the soil phases.

Mechanochemistry of the 5f-element compounds

The effect of the mechanical treatment of UO2(NO3)2·6H2O in a planetary ball mill in air and as a suspension in toluene has been studied. The X-ray diffractometry results strongly suggest that part of the mechanoactivated material is transformed in nitrosyl uranyl nitrate.

Influence of ThO2 on the photocatalytic activity of TiO2

AbstractMicrocomposites consisting of TiO2 (or Ce-doped TiO2) and ThO2 (0.5–2% of the TiO2 mass) are produced by sol-gel synthesis of TiO2 in presence of ThO2. X-ray diffraction study reveals the effects of ThO2 (compared to the ThO2-free TiO2, obtained by the same method) on the anatase interplanar distances, crystallites size and phase composition. The photocatalytic tests in presence of the composites under UV irradiation reveal an increase of the Malachite Green degradation rate constant. The effect depends on the Th relative content, temperature of annealing of the catalyst and addition of other doping agent. The highest photocatalytic activity is observed for TiO2 obtained at 550°C and containing 1% ThO2. The composite exhibits activity in dark, also. The presence of Ce4+ ions is not an obligatory requirement for the realization of the ThO2 effect. The reported results suggest that the radioactivity of the Th and/or its decay products is one of the main factors responsible for the increased photocatalytic activity of TiO2.

Mechanochemistry of the 5f-element compounds Part 2. Mechanochemically induced change in coordination mode of UO2(CH3COO)2.2H2O

The effect of the mechanical treatment of UO2(CH3COO)2·2H2O in a planetary ball mill in air or as a suspension in toluene or benzene on its crystal structure and coordination mode has been studied. No significant changes in the crystal structure are observed. IR-spectroscopy results suggest that in the part of the mechanoactivated material the bidentate bonding of the CH3COO− is transformed in monodentate one. The newformed species is soluble in non-polar solvents.

Common organics as samples to measure radioxenon after nuclear emergency

Radioactive isotopes of xenon are key radionuclides to be monitored in case of nuclear emergency and for control of the Nuclear Non-Proliferation Treaty and the Comprehensive Nuclear Test-Ban Treaty. In case of nuclear emergency the concentrations of radioxenon in the close vicinity of the nuclear event are high and can exceed the dynamic range of radioxenon monitors, as it was observed after Fukushima Dai-ichi accident. Some organics have high absorption ability for noble gases. We explored the feasibility of such organics to serve as samples to measure radioxenon. Experiments were organized in which samples of salo (fatback), butter, cosmetic and medical greasy creams and pieces of DVDs were exposed to 131mXe concentration of 7.105 Bq m-3. Additional exposure to 222Rn at similar concentration was made to study whether 222Rn can be a proper surrogate for extensive laboratory studies needed to develop this method for practical application. The specimens were measured by liquid scintillation counting. The results showed that the signal from all specimens is well above the detection limits and remains quantitatively measurable even when the samples are taken for analysis with sufficient delay (up to 30 h) after the end of exposure. The other conclusion is that the desorption properties of samples exposed to 222Rn are similar to that exposed to 131mXe and therefore, 222Rn can be considered as proper radioxenon surrogate for laboratory studies on the method.

The radioactivity and the chemical nature of additives as factors determining the photocatalytic activity of TiO2

AbstractMicrocomposites consisting of TiO2 and ThF4 or UO3 (0.5–2% of the TiO2 mass) are produced by sol-gel synthesis of TiO2 in presence of the respective additives. X-ray diffraction study reveals small effect of the latter on TiO2 phase composition and cell parameters and significant influence on the crystallite size and UV/Vis reflectance spectra. The photocatalytic tests in presence of TiO2-ThF4 microcomposites under UV and solar irradiation show a non-monotonic increase of the Malachite Green degradation rate constant with the increase of ThF4-content. No changes in the photocatalytic activity are observed in the presence of UO3 but the latter composites exhibit activity in darkness. The results are compared with previously reported data on the performance of TiO2-ThO2 photocatalyst with the same radioactivity and suggest that both radioactivity and the chemical nature of the dopants are responsible for the photocatalytic performance of TiO2-based composites containing radioactive substances.