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The interaction of oxygen with solid lead selenide samples prepared in the form of bulk single crystals, films, pressed pellets, and powders is investigated in the temperature range 298-823 K at exposure times of 5-240 min and an oxygen pressure of ~10 5 Pa. All samples are produced from a lead selenide batch heat treated under dynamic vacuum. It is revealed that, under the given thermodynamic conditions, the PbSeO 3 phase is formed on the surface of all the PbSe samples beginning with room temperature. No phase transformations are observed in the sample bulk. Lead selenite is synthesized using lead selenide precursor by the solidphase method in an oxygen atmosphere at temperatures considerably lower than the melting temperature. At the intermediate synthesis stage, it is possible to prepare lead selenide nanocrystalline structures embedded in a PbSeO 3 dielectric matrix.

Two kinds of LX-ray emission effects have been studied: the chemical shifts (Ch. S.) in compounds of Th, U, and Np and the isotope shifts (I. S.) between 235U and 238U. The effects are interpreted on the basis of the Atomic Structure Calculations in terms of the model of the "isolated atom-ion". It gives the partial effective charges (Q5fand Q6d ) which are applied for the search for relativistic effects in U5f § -electron states, to set a correlation with magnetic data. The values ofI. S. (235U -238U) were observed for the first time in 11 UL emission lines and shown distinctly to correlate with the theoretical Nvolume -size effectN throughout all U L-lines studied.

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