Vol 58, No 5 (2016)

The compounds [Th(NpO₂)₆(H₂O)₈(OH)Cl₉]·H₂O (I) and [Th(NpO₂)₆(H₂O)₉Cl₉]Cl (II), in which mixed-element Th(IV)/Np(V) cation–cation interaction is observed, were isolated in the form of single crystals and studied by X-ray diffraction. The NpO₂⁺···NpO₂⁺ cation–cation bonds link the dioxocations into six-unit rings, and the NpO₂⁺···Th⁴⁺ bonds link these rings into a three-dimensional network. The compounds also contain a hydroxide ion incorporated in the Th⁴⁺ coordination surrounding or a chloride ion located in the interlayer space, depending on the synthesis conditions. The Np(V) pentagonal bipyramids in I and II are characterized by equal, within the uncertainty, bond lengths. The equatorial planes of the bipyramids are formed by three Cl^– anions, oxygen atom of the adjacent NpO₂⁺ cation, and oxygen atom of the water molecule. The Th⁴⁺ cations in I and II have the coordination surrounding in the form of tricapped trigonal prisms (CN 9) whose quadrangular lateral faces are formed by the oxygen atoms of the NpO₂⁺ cations and are capped by three water molecules. The Th⁴⁺ cations in I and II are arranged in the interlayer space, binding three cyclic moieties from each of the two adjacent layers.

A series of isostructural compounds of the composition Na₇H[EMo₁₂O₄₂]·12H₂O, where E(IV) = Ce, Th, U, Np, or Pu, were synthesized and structurally characterized. In the [EMo₁₂O₄₂]^8– heteropolyanion (HPA), the central E(IV) atom is surrounded by six Mo₂O₉ groups, each constituted by two octahedra sharing a common face. The coordination polyhedron (CP) of the central atom is a weakly distorted icosahedron with the mean E(IV)–О bond lengths of 2.498, 2.529, 2.500, 2.490, and 2.488 Å for Ce, Th, U, Np, and Pu, respectively. In the structure of the compounds Na₇H[EMo₁₂O₄₂]·12H₂O, there are two crystallographically independent sodium atoms: Na(1) and Na(2). The oxygen surrounding of the Na(1) atom is formed by the terminal oxygen atoms of two heteropolyanions adjacent along [001], and its coordination polyhedron is an octahedron. The surrounding of the Na(2) atom (a six-vertex polyhedron) is formed by three terminal oxygen atoms of three Mo₂O₉ groups belonging to the same HPA and by three water molecules. The coordination polyhedra of the Na(2) atoms are linked with each other via common oxygen atoms of O_w(2) water molecules to form a chain “winding” around the 3₁ screw axis. The heteropolyanions and Na⁺ cations in the crystal form a framework constructed in a fashion characteristic of Dexter–Silverton type anions, with the coordination via three terminal oxygen atoms of three Mo₂O₉ groups. Excess negative charge of HPA is compensated by the proton localized on one of the six bridging O atoms. In the Mo₂O₉ doubled octahedra, the Mo–O bonds with the О atoms bonded to E(IV) and forming the edge of the common face are sensitive to the kind of the central atom.

A mathematical model describing the solubility of barium, strontium, and lead nitrates in nitric acid solutions containing 0 to 14 M HNO₃ in the temperature range from 0 to 90°С with the error no larger than 7% was developed. The model is based on the reactions of metal precipitation in the form of Me(NO₃)₂ at HNO₃ concentrations of up to 7–8 M and Ме(NO₃)₂·2HNO₃ at higher nitric acid concentrations, and also on the assumed formation of soluble metal nitrate complexes MeNO₃⁺. A sharp increase in the barium solubility at HNO₃ concentrations lower than 0.5 M and temperatures of 50 and 90°С was interpreted assuming the possible formation of dimeric oxocations Ba₂O₂⁺ or associates Ba₂(OH)₂²⁺. A model describing the solubility of barium nitrate in the presence of strontium nitrate in HNO₃ solutions at HNO₃ concentrations in the range from 0 to 5 M was also suggested.

The effect of HNO₃ on the thermal stability and radiation resistance of trifluoromethyl phenyl sulfone (FS-13) used as extractant diluent in high-level waste partitioning was studied. Heating of FS-13 in the presence of 14 M HNO₃ is not accompanied by exothermic effects up to 160°С. The amount of gaseous products released in the course of heating the system consisting of FS-13 and HNO₃ and the composition of the major radiolysis products of the system components at irradiation doses of up to 0.5 MGy were determined.

A cell for isolating ¹⁷⁷Lu from a neutron-irradiated ¹⁷⁶Yb target was developed. The procedure involves a combination of two processes: contact reduction of Yb from acetate–chloride solution on sodium amalgam, followed by electrolysis of the solution on a mercury cathode. The process conditions were chosen so that the adjustment of the working solution characteristics (composition, pH, etc.) in going from contact reduction to electrolysis was not required. Both processes are performed in one cell, which reduces the ¹⁷⁷Lu loss. On an installation consisting of two cells, the decontamination factor of the ¹⁷⁷Lu solution from Yb of up to 10⁶ was reached, which is necessary for obtaining a ¹⁷⁷Lu preparation of high specific activity.

The results of the development of a medical-purpose extraction ¹⁸⁸Re generator and of ¹⁸⁸Re radiopharmaceuticals are presented. The main advantage of this generator is the possibility of using as starting material tungsten oxide of natural isotope composition, irradiated in a reactor with medium neutron flux [(1.0–1.4) × 10¹⁴n cm^–2 s^–1]. Separation of the parent ¹⁸⁸W and daughter ¹⁸⁸Re was performed in a centrifugal semicounter-current contactor developed at the Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. The ¹⁸⁸Re yield is about 90%, and the radiochemical purity (Na¹⁸⁸ReO₄ content) is ≥95%. The content of the ¹⁸⁸W impurity is less than 1 × 10^–3% relative to the ¹⁸⁸Re activity, and the content of other radionuclides is less than 1 × 10^–4%. The resulting Na¹⁸⁸ReO₄ solution was registered as “Active pharmaceutical substance” and was used in the development and subsequent preclinical trials of several radiopharmaceuticals for radionuclide therapy of pain syndrome accompanying the development of cancer metastases into the skeleton, and also for radiosynovectomy.

2-[2-(4-(Dibenzo[b, f][1,4]thiazepin-11-yl)piperazin-1-yl)ethoxy]ethanol (Quetiapine) labeled with ¹⁴C in 11-position was synthesized in five steps from [carboxy-¹⁴C]anthranilic acid. The key precursor of the target product is [11-¹⁴C]dibenzothiazepin-11(10H)-one. The reaction is performed as one-pot process.

An ultradisperse technology is suggested for consolidation of partitioned product concentrates in an iron–lanthanum silicophosphate ceramic host material. The technology is economically advantageous because of the use of readily available reagents and raw materials and takes a short time owing to the composite structure of the host material. The latter factor also ensures high corrosion resistance of the host material. The process allows the development of a robotic system for nuclear waste packing directly in the container crucible. It is appropriate to isolate the ready nuclear containers in a superdeep borehole repository.

The distribution of ²¹⁰Pb in the sediment samples of major rivers of coastal Kerala, namely, Bharathapuzha, Periyar, and Kallada, was studied systematically. The activity of ²¹⁰Pb was estimated through ²¹⁰Po by radiochemical separation and subsequent deposition on a silver disc. The α-activity was then counted using a ZnS(Ag) counter of 30% efficiency, and the activity was calculated. The mean activities of ²¹⁰Pb in the sediment samples of Bharathapuzha, Periyar, and Kallada rivers were found to be 13.5 ± 1.2, 89 ± 3, and 61 ± 2 Bq kg^–1, respectively. Good correlation was found between the ²¹⁰Pb activity and organic matter percentage and clay content for Periyar and Kallada rivers.