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Abstract  

Results of a self-observation of the working time distribution of an university teacher for a period of 28 years are reported. Averaged over the whole period, the teaching activities take 18%, scientific work −20%, and the various kinds of administrative, organizational and technical activities −51% of the working time. The changes of the working time distribution and of the working day duration during the years and the respective data related to the months in the year are presented. The working time data are compared with the growth of the scientific production of the observed person.

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Abstract  

The paper presents a comprehensive review of radioanalytical methods for chemical identification of radioactive sulfur atoms recoiling in neutron irradiated (or implanted) inorganic systems.

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Abstract  

A method is proposed for neutron activation determination of U via239Np. This is separated by coprecipitation of ZrO(H2PO4)2 and its 106 keV γ-peak measured. The sensitivity of the determination is 10−9 g. The method is based on the well-known ability of Np(IV) to coprecipitate with zirconium phosphate, while Np(VI) does not form insoluble phosphates or fluorides. This permits elimination of elements interfering, with the determination of239Np via the 106 keV γ-peak: Sm, Nd, Yb, Lu, Pa (from Th) and Ta. The rare earths are eliminated by coprecipitation on LaF3, and Pa and Ta as insoluble phosphates in an oxidizing medium. The method is suitable for phosphorus-containing samples: phosphorites, apatites and their industrial treatment products. The results obtained for the uranium content with the proposed method are in good agreement with the results of other methods and authors.

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Abstract  

The uranium contents in phosphorites from North Africa, products of their processing (H3PO4, superphosphates, phosphogypsum), lignites from South Bulgaria and products of their burning, copper ores and concentrates have been determined by instrumental and radiochemical NAA. An evaluation of the contribution of the phosphoric fertilizers to the uranium content of soil, plants, breeding stock and man has been done.

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Abstract  

The structure changes and the degree of reduction of U3O8 after mechanoactivation in agate and stainless steel vessels in different media are studied. Clearly expressed reduction of U(IV, VI) oxide, accompanied by oxygen release as a result of mechanochemical activation is observed. The highest degree of reduction is reached when mechanoactivation is performed in suspension with nonpolar organic solvents. The presence of acetaldehyde as a reducing agent did not cause valuable increase of the reduction process. Quantitative evaluation of the mechanochemically induced changes in the crystal structure of U3O8 is done. Decrease of the crystallite sizes of both the U3O8 and the reduced form, provoked by the mechanochemical treatment is observed for all the samples. No other uranium-contained compounds, formed during the mechanoactivation in the different media and mixtures were found.

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Abstract  

The distribution of35S is investigated by autoradiography in neutron irradiated sodium and potassium chloride crystals cleaved from Kyropoulos grown single crystals of high purity.

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Abstract  

A method for210Po determination in air is developed which includes sucking of known volume of air through aerosol filter typ AFA-XA, wet combustion of the filter by a mixture of conc. H2SO4 and conc. HNO3, deposition of210Po on nickel plate from hydrochloric acid solution at 90°C. The chemical yield is (90.7±5.4)% and radioisotope purity of the final sample (concerning α-emitters) fully satisfactory. If 3 m3 air is sucked the detection limit is 10−17 Cf210Po/1 air.

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Abstract  

Method for synthesis of UO2+x and uranium–thorium mixed oxides by using sol–gel method and mechanochemical activation is proposed. The synthesis of UO2+x and solid solutions with equal amount of metals or enriched to one of them is performed by external gelation process, thermal decomposition of the sol–gel products in air and subsequent mechanochemical activation in air in stainless steel vessels. The crystal structures of the obtained oxides before and after the mechanochemical treatment are analysed by the use of X-ray diffraction method. Quantitative phase analysis and calculations of the size of the crystallites, lattice parameters, and densities of the oxides are performed by BRASS program for Rietveld calculation. The proposed method leads to decrease of the lattice parameters and thus to higher density of the obtained oxides with crystallites size in the range of 12–16 nm.

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Mechanochemistry of the 5f-element compounds

Part 2. Mechanochemically induced change in coordination mode of UO2(CH3COO)2·2H2O

Journal of Radioanalytical and Nuclear Chemistry
Authors:
P. Kovacheva
,
N. Minkova
,
D. Todorovsky
, and
D. Radev

Abstract  

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.

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Mechanochemistry of the 5f-element compounds

Part 3. Mechanochemically stimulated formation of nitrosyl uranyl nitrate

Journal of Radioanalytical and Nuclear Chemistry
Authors:
P. Kovacheva
,
N. Minkova
,
D. Radev
, and
D. Todorovsky

Abstract  

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.

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