Vol 61, No 6 (2019)

Targeted radionuclide therapy (TRT) is today one of the most effective methods for tumor treatment. The use of the theranostic concept allows personalized approach to the choice of treatment tactics, based on diagnostic investigation using molecular imaging methods, among which PET is the most sensitive and informative. The main theranostic isotope pairs and the corresponding radiopharmaceuticals for TRT, based on β-emitters used in clinical practice, are briefly considered, and the possibilities and limitations of the well-known agents and prospects for using new radiopharmaceuticals in TRT are discussed.

A procedure was developed for preparing powders of solid solutions of uranium dioxide with 3 or 10 wt % Ce (as Am surrogate) from nitric acid solutions using microwave radiation. The powders obtained consist of particle aggregates of size no larger than 400 µm; the fraction of particles of size smaller than 25 µm does not exceed 1 wt %. The tap density of the powders is 2.3–2.5 g cm⁻³, and their specific surface area is 2.2–2.5 m² g⁻¹. The powder characteristics meet the requirements to powders of ceramic quality for nuclear fuel fabrication. The method developed can be used for producing mixed U-Am oxides on a unit for spent nuclear fuel reprocessing at the Pilot Demonstration Power Engineering Complex with the aim of Am transmutation in the BREST-OD-300 reactor.

Thermal stability of hydrazine nitrate (HN) in solutions in 4–12 M HNO₃ in the temperature interval 70–150°C was studied. Exothermic reactions accompanied by gas evolution arise in such systems under definite conditions. The intensity of such reactions depends on the component concentrations and temperature. The characteristics of the exothermic processes were determined to evaluate the explosion safety of process operations. Because of sharp pressure buildup in apparatuses, exothermic processes in the course of evaporation of HN-containing nitric acid solutions are hazardous from the viewpoint of radiation accidents.

A series of novel structurally related glutaramides (GAs) were synthesized and applied to the extraction and separation of selected actinides and lanthanides from nitric acid medium. The influence of the nature of the alkyl chain on the distribution ratio of U(VI) and Th(IV) was examined. N,N′-Dimethyl-N, N′-dioctylglutaramide (DMDOGA) and N, N′-dihexyl-N, N′-dioctylglutaramide (DHDOGA) were chosen and applied to the selective extraction and separation of U(VI), Th(IV), and selected lanthanides Ln(III) [Nd(III), Eu(III), Gd(III), Sm(III), and Dy(III)]. The distribution ratios of U(VI) and Th(IV) were determined in relation to the diluent type, shaking time, nitric acid concentration, salting-out agents, concentration of substituted glutaramide, and temperature. The extraction of lanthanides is negligible in the entire studied range of HNO₃ concentrations (0.1–7 M). With an increase in the HNO₃ concentration, the extraction of U(VI) increased up to 5 M HNO₃ and then decreased on further increase in the acidity, whereas the extraction of Th(IV) slowly increased with the HNO₃ concentration in the entire range studied. The stoichiometry of the U(VI) and Th(IV) extractable species was determined to be UO₂(NO₃)₂·2GA and Th(NO₃)₄·GA, respectively. The IR spectra of the extracted species were recorded. Both DMDOGA and DHDOGA are more selective to U(VI) compared to Th(IV) in HNO₃ solutions. Good separation of U(VI) from Th(IV) can be achieved at 0.1–0.5 M HNO₃. The back-extraction of U(VI) and Th(IV) from the organic phase was also studied.

The extraction of REE(III), U(VI), and Th(IV) from nitric acid solutions with solutions of diphenyl(dibutylcarbamoylmethyl)phosphine oxide considerably increases in the presence of ionic liquids with the bis[(trifluoromethyl)sulfonyl]imide anion and quaternary ammonium cations. The stoichiometry of the extractable complexes was determined. The influence of the HNO₃ concentration in the aqueous phase, of the cation in the ionic liquid, and of the organic diluent on the efficiency of the extraction of REE(III), U(VI), and Th(IV) ions was examined.

Sorbents based on manganese oxides were prepared by KMnO₄ reduction in aqueous-ethanol medium. The influence of the synthesis conditions (temperature and time of the sol-gel synthesis, type of structure-forming cations, calcination temperature) on the pore structure and on the performance and selectivity in ⁹⁰Sr sorption was studied. The sorbents have the mesoporous structure with the specific surface area of 180–220 m² g⁻¹ and mean pore size of 10–20 nm. Manganese oxide of channel structure in the Na⁺ form, prepared by the reaction at 25°C for 5 h and heat-treated at 350°C, exhibits the highest performance and selectivity in ⁹⁰Sr sorption (distribution coefficient K_d = 1.04 × 10⁴ cm³ g⁻¹, Sr-Ca separation factor D_Sr/Ca = 99). The sorbents synthesized exhibit the highest performance and selectivity in neutral and alkaline media.

The ability of cerium(IV) hydrogen phosphate Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5 to adsorb radionuclides was studied. The degree of sorption from aqueous solutions exceeds 95% at pH > 7 for Np(V), at pH > 9 for Sr(II), at pH > 5 for Am(III) and U(VI), and at pH > 2 for Th(IV). The radionuclides are rapidly and quantitatively leached from the sorbent surface in acid solutions; i.e., the sorption is reversible.

Crude uranium concentrate (30–35.8% U) from G. Gattar pilot plant, North Eastern Desert, Egypt, produced by acid heap percolation leaching, was upgraded by 1,5-diphenylthiocarbazone-modified Amberlite XAD-7 (H₂Dz-XAD-7). The modified resin was characterized by EDAX, SEM, CHNSO analysis, and FTIR. The purified cake was characterized by XRD, EDAX, and ICP-OES techniques.

A ¹³⁷Cs-loaded sealed source was prepared by contacting silicotitanate gel with a ¹³⁷Cs solution at pH 7 for 48 h at 25°C, drying at 100°C for 24 h, placing as a radioactive core inside a central cylindrical cavity in a base Perspex half-disc, and assembling a top Perspex half-disc with the base one using epoxy adhesive. The sealed source prepared was standardized using a γ-ray spectrometer and various calculation methods including DETEFF code and different ways of the efficiency transfer concept. For higher accuracy, the effect of the HPGe detector contamination background at different measurement distances was studied. The prepared sealed source was found to have a ¹³⁷Cs activity of 0.98 ± 0.06 kBq.

Ropinirole, a non-ergoline dopamine agonist, was labeled with ^99mTc tricarbonyl {[^99mTc(CO)₃·(H₂O)₃]⁺} with the aim of obtaining a new brain imaging agent. For in vivo use, the radiosynthesis of ^99mTc tricarbonyl ropinirole was performed by heating a solution containing ropinirole and the precursor, ^99mTc tricarbonyl, on a boiling water bath for 30 min. The influence of the substrate amount and pH on the reaction was studied to optimize the synthesis. The biodistribution and scintigraphic studies demonstrate the suitability of ^99mTc tricarbonyl ropinirole as a novel tracer for brain tumor imaging.

The extraction parameters and speciation of ¹³⁷Cs and ²⁴¹Am in bottom sediments of reservoir R-17 of the Mayak Production Assocation were studied. The extraction was performed with four solutions with different pH values (water simulating in its composition the groundwater from the investigated area, 0.1 M Na₂CO₃, acetate buffer solution, and 1 × 10⁻³ M HNO₃). With the first solution, the degree of extraction of ¹³⁷Cs and ⁹⁰Sr becomes constant in 24 h. The desorption percentage did not depend on pH. The ¹³⁷Cs distribution coefficients were calculated. The lowest values were observed in the buffer solution (27) and sodium carbonate solution (21), and the highest values, in water (9250). As shown by sequential extraction, the major fraction of cesium (90%) occurs in the insoluble form. Incorporation into the crystal lattice of clay minerals was found to be the main sorption mechanism. The ²⁴¹Am sorption mainly occurs by the mechanism of complexation with carbonates.