Vol 61, No 3 (2019)

The main deuterium and tritium sources used for preparing hydrogen isotope labeled compounds are presented. The mechanisms of hydrogenation and isotope exchange in organic compounds in the presence of heterogeneous and homogeneous catalysts when using gaseous tritium (or deuterium) or tritium (or deuterium) water are considered. Examples of the participation of solvent protons in introduction of deuterium and tritium into organic compounds by dehalogenation are presented. The problem of selective hydrogenation and dehalogenation is briefly discussed. Particular attention is paid to isotope exchange with deuterium or tritium in the presence of homogeneous iridium catalysts.

The structures of three new Np(V) complexes [(NpO₂)₂(phen)₂(C₇H₅O₂)₂] (I), [(NpO₂)₂(phen)₂. (o-C₇H₄FO₂)₂] (II), and [(NpO₂)₂(phen)₂(p-C₇H₄FO₂)₂] (III), where phen = 1,10-phenanthroline, were studied. Two NpO₂⁺ cations in the complexes are bound to each other by cation-cation bonds in which both neptunyl(V) ions act with respect to each other as lignads and as coordination centers simultaneously, forming dimeric An₂O₄²⁺ cations. In complexes I–III, each Np atom has the coordination polyhedron (CP) in the form of a pentagonal bipyramid with the “yl” O atoms in the apical positions; the neptunyl(V) groups are appreciably nonlinear. The equatorial plane of the bipyramids is constituted by two N atoms of phenanthroline, O atom of the other NpO₂⁺ cation, and two O atoms of the C₆H₅COO^- (I), o-C₆H₄FCOO^- (II), and p-C₆H₄FCOO^- (III) anions. The Np⋅⋅⋅Np interatomic distances in the dimetic NpO₂⁺ cations (Å) are 3.40519(17) (I), 3.43891(17) (II), and 3.4271(3) (III). The main differences in the structures of I–III are manifested in the conformational characteristics and are caused by the effect of C-H⋅⋅⋅O and C-H⋅⋅⋅F hydrogen bonding.

Gas-phase conversion of UC in NO_x-air, NO_x-H₂0 (vapor)-air, and HN0₃ (vapor)-air atmospheres in the temperature interval from 298 to 673 K was studied. In the course of the gas-phase conversion in an NO_x-air atmosphere, UC transforms into uranium oxides and oxyhydroxides; uranyl nitrates and hydroxyni-trates are formed in smaller amounts. In NO_x-H₂0 (vapor)-air and HN0₃ (vapor)-air atmospheres, the major conversion products are uranyl nitrate hydrates, with the nitration occurring at a lower temperature than in an NO_x-air atmosphere.

Multiwalled carbon nanotubes were used for the synthesis of five different polyacrylamide/ MWCNT composites. Different polymerization techniques were applied, namely, copolymerization, template polymerization of monomers on polyacrylamide, or grafting method, all induced by γ-irradiation. Fourier transform IR spectra were used for characterization. These composites were used for studying the adsorption and separation behaviors of Co(II) and Eu(III) under various experimental conditions. Radioactive isotopes ⁶⁰Co and ^152+154Eu were used for tracing the corresponding elements. The adsorption on the related polymers was also studied for comparison. The K_d values for the adsorption on the nanocomposites were found to be much higher than those on the corresponding polymers. Complete adsorption was achieved on some of the synthesized nanocomposites under definite conditions, suggesting the possibility of complete isolation of Co(II) and/or Eu(III) from large volumes of aqueous solutions. Separation of Co(II) and Eu(III) from each other was also found to be possible under certain conditions.

The dynamics of the ²²³Ra distribution in the volume of spherical hydroxyapatite (HAP) granules in the course of the ²²³Ra sorption from aqueous solutions onto sorbent particles and desorption was studied by α-track radiography. The optimum time of contact of the sample with a detector (exposure) was found, and a procedure for preparing experimental samples was suggested. Taking into account the density of the porous sorbent, the ranges of the α-particles emitted by ²²³Ra and its daughter products and of the recoil nuclei were estimated. The averaged effective range of the α-particles in HAP is ∼35 μm. A mathematical model of the Ra diffusion into the depth of the porous sorbent, taking into account the sorption, was developed on the basis of the parameters obtained. The effective diffusion coefficient was estimated at ∼3 × 10^–5 cm² s^–1. Correlation be¬tween the sorbent particle size, radionuclide sorption time, and the absorbed dose produced by the particle in a biological tissue was demonstrated.

The specific emission rates of iodine isotopes into the atmosphere during normal operation of European and Russian NPPs with different types of reactor facilities were analyzed. The probability distributions for the specific parameters are asymmetric, and their median values tend to decrease. Three categories of NPPs were distinguished: those with the best, worst, and stable practice of the ¹³¹I emission. The current global atmospheric release of ¹²⁹I from all the NPPs in the world is estimated at 0.8 kBq year⁻¹. With an increase in the total installed NPP capacity to 632 GW, the global release of ¹²⁹I from the NPP emissions will increase to 1.4 kBq year⁻¹, which is two times lower than the rate of natural production of this nuclide from atmospheric Xe isotopes under the action of cosmic rays. Based on the measurements performed at separate Russian NPPs, the contribution of the aerosol and gaseous iodine forms to the total volume activity of the released iodine isotopes was determined. Under the conditions of normal NPP operation, gaseous iodine compounds make the prevalent contribution to the radioiodine emissions (65–85%).

Occupational exposures to radiation during chemical treatment of black sand minerals (ilmenite, zircon, monazite, rutile) were evaluated. Additive effective dose rate (AEDR) is a new measure introduced to control the occupational exposure to radiation. The value of AEDR from the external γ-rays was estimated at 1.06 × 10^–9 Sv h^–1 kBq^–1. Based on the dose conversion coefficients obtained by the previous epidemiological studies, AEDR from radon and thoron gases was found to be 2.7 × 10^–9 and 1.52 × 10^–9 Sv h^–1 kBq^–1, respectively. The batch effective dose (BED) was suggested as a real alternative to the average effective doses over different locations. It is concluded that 1 kBq of a natural radioactive mineral adds an occupational effective dose of 9.52 × 10^–5 Sv year^–1.