Volume 95, Issue 1

The extraction behavior of rutherfordium (Rf) into tributylphosphate (TBP) from hydrochloric acid (HCl) has been studied together with those of the lighter group-4 elements Zr and Hf. The extractability of 261 Rf, 169 Hf, and 85 Zr into TBP was investigated under identical conditions in 7.2–8.0 M HCl by on-line reversed-phase extraction chromatography. The percent extractions of Rf, Hf, and Zr into the TBP resin increase steeply with increasing HCl concentration, and the order of extraction is Zr > Hf ≈ Rf. By considering the order of chloride complexation among these elements, it is suggested that the stability of the TBP complex of Rf tetrachloride is lower than those of Zr and Hf.

Tetravalent plutonium readily undergoes hydrolysis even in highly acidic aqueous solutions. In the past, many attempts were made to quantify hydrolysis species by means of optical absorption spectroscopy. In the present work solutions ranging from 10 −5 M to 10 -2 M (total Pu) concentration in 0.5 M HCl/NaCl (0.3 < pH c < 2.1) are carefully investigated by combining absorption-spectroscopy (UV-Vis, liquid core waveguide capillary) and laser-induced breakdown detection, with special emphasis on the limited solubility of Pu(IV). The results clearly indicate that all changes in the absorption spectra originate from the formation of Pu-polyspecies and colloids. The molar absorptivity of mononuclear Pu(IV) hydroxide complexes does not vary with increasing pH c and ongoing hydrolysis. The normalized absorption spectra of at least the first and the second hydroxide complex (Pu(OH) n 4- n n = 1, 2) do not differ from those of the hydrated Pu 4+ ion.

The adsorption of U(VI) onto peat moss has been studied as a function of uranium concentration, pH, shaking time and ionic strength. The pH and ionic strength of the solution markedly affect the extent of removal. The attainment of equilibrium is fast and the equilibrium data fit well the Freundlich, Langmuir and Dubinin-Radushkevich equations. A probable mechanism of uptake is discussed. Further studies demonstrate that under optimum conditions peat moss can be used for the treatment of waste solutions containing low concentrations of uranium.

The oxidative alteration of uraninite and the fate of trace elements (Y, LREE, Zr, and Th) in a granite-hosted uranium ore deposit in north Guangdong province, China, were investigated to understand the geochemical behavior of spent UO 2 fuel and associated fission products and transuranium elements under oxidizing conditions. In light of the paragenetic relationship of the alteration products, two alteration series of uraninite were identified: one is the silicate series with a mineral paragenesis of uraninite → uranyl oxide hydrates → Si-rich uranyl phase → uranophane (Ca[(UO 2 )(SiO 3 OH)] 2 (H 2 O) 5 ), and the other is the phosphate series with a mineral paragenesis of uraninite → uranyl oxide hydrates → autunite (Ca[(UO 2 )(PO 4 )] 2 (H 2 O) 6 ) → yingjiangite ((K 2 ,Ca)(UO 2 ) 7 (PO 4 ) 4 (OH) 6 (H 2 O) 6 ). In contrast to the wide distribution and abundance of uranophane and the uranyl phosphate minerals, uranyl oxides were only occasionally found in the ore samples, suggesting that the uranyl silicates and phosphates should be the predominant alteration products of UO 2 under oxidizing conditions, although uranyl oxide hydrates would be the solubility-limiting phase of uranium in the very early stage of alteration. Furthermore, the interlayer cation of the uranyl phases in the Xiazhuang uranium ore field is dominated by Ca 2+ , indicating that the release of uranium and other radionuclides will be limited mainly by uranophane and autunite during the oxidative alteration of spent UO 2 fuel in underground repositories where enhanced calcium concentration is expected due to cement/water reactions. Compositionally, the cation atomic ratios in uranyl phases often deviate considerably from their respective stoichiometric values as indicated by the nominal formulae, but the compositional variation does not result in significant structural change as indicated by X-ray diffraction patterns. This observation indicates that the structure of U 6+ minerals may easily be adjusted to accommodate impurity elements including crystallographically compatible radionuclides. Compared with the primary uraninites, the secondary minerals are slightly enriched in light REE, but significantly depleted in Y 3+ probably due to its cation-radius mismatch with interlayer Ca 2+ . The apparent enrichment of Zr 4+ in uranophane and uranyl phosphates relative to uraninite may result from the coupled substitutions: Zr 4+ ↔ U 6+ and REE 3+ ↔ Ca 2+ (K + ). Because an adequate charge-balance mechanism and significant distortion of the coordination polyhedra are required for the substitution An 4+ ↔ U 6+ , this type of substitution may not be common.

PET imaging of the μ -opioid receptor (OR) is still restricted to [ 11 C]carfentanil ([ 11 C]CFN) but its use is limited due to its short half-life and high agonistic potency. Recently, the radiosynthesis of [ 18 F]fluoroalkyl esters of CFN was proposed, unfortunately yielding products not suitable for human PET due to their low specific activities. Therefore, our rationale was to develop a reliable radiosynthesis of a [ 18 F]fluoroethylated CFN derivative overcoming these drawbacks. The [ 18 F]fluoroethyl ester of carfentanil, [ 18 F]FE@CFN (2-[ 18 F]fluoroethyl 4-[ N -(1-oxopropyl)- N -phenylamino]-1-(2-phenylethyl)-4-piperidinecarboxylate), and its corresponding inactive standard compound were prepared. Purification of [ 18 F]FE@CFN was achieved via a simple solid phase extraction method. [ 18 F]FE@CFN was prepared with excellent purity (> 98%) and sufficient yields. Specific activity surpassed the level required for safe administration. We therefore conclude that our simplified synthesis of [ 18 F]FE@CFN, for the first time, overcomes the shortcomings of [ 11 C]CFN and the previously suggested alternatives, namely, (1) longer half-life; (2) easy production and (3) adequate specific activity, should make a wider application possible. Hence, [ 18 F]FE@CFN may become a valuable PET tracer for the imaging of the μ -OR in human brain and heart.

The most commonly used radiometal for dosimetry in radioimmunotherapy is 111 In. This radionuclide has suitable physical properties and its chelation chemistry is similar to that of 90 Y, which is frequently used in radiotherapy. Since imaging with a γ -ray emitting radionuclide is less accurate than PET-imaging, we evaluated the labelling of a monoclonal antibody with the β + -emitter 68 Ga and the in vitro stability of the labelled antibody in human serum. We focused our studies on the bifunctional chelators Bn-DTPA, CHX-A ′′ -DTPA, and mx-DTPA conjugated to the anti-CD45 monoclonal antibody YAML568. The incorporation of 68 Ga into the antibody is rapid for all three ligands. After 5 minutes the radiochemical yield is > 95%. The serum stability differs strongly depending on the chelator. The least stable chelate is [ 68 Ga]Bn-DTPA. After 3 h at 37°C in human serum 66% of 68 Ga is transchelated from the antibody to transferrin. The [ 68 Ga]CHX-A ′′ -DTPA chelate is kinetically more stable. 83% of 68 Ga were still chelated to the antibody after 4h in human serum. The best results were obtained using mx -DTPA. Only 5% were transchelated from the labelled antibody to transferrin after 4h in human serum. The high in vitro stability and the low transchelation tendency of the [ 68 Ga] mx -DTPA-conjugate enable the accurate determination of antibody biodistribution for dosimetry using PET in combination with conventional [ 111 In]anti-CD45 scintigraphy.

The need exists for preconcentration of trace and ultratrace amounts of uranium from environmental, geological and biological samples. The adsorption of uranium on various solids is important from the purification, environmental, and radioactivity waste disposal points of view. A method is described for the determination of traces of uranium using first-derivative spectrophotometry after adsorptive preconcentration of uranium on activated carbon. Various parameters that influence the adsorptive preconcentration of uranium on activated carbon, viz. , pH, amounts of activated carbon and time of stirring and interference of metals have been studied. First-derivative spectrophotometry in conjunction with adsorptive preconcentration of uranium on activated carbon is used for determining uranium at concentration levels down to 20 ppb (w/v).

Sorption of europium, Eu(III) with polymeric silicic acid has been studied under varying experimental conditions such as pH, ionic strength ( I ), concentration of silicic acid and of Eu(III), the presence of carbonate ions, and aging time. Sorption studies of Eu(III) at pH 7.50 ± 0.50) and I = 0.20 M NaClO 4 indicate 1.32 ± 0.06 × 10 -5 M Eu as the Critical Coagulation Concentration, CCC. Sorption of Eu(III) on colloidal silica increases with increased ionic strength from 80% (0.20 M NaClO 4 ) to 93% (0.89 M NaClO 4 ). The coagulation process is favored by an increase in silica concentration. The influence of CO 3 2- (1.00 × 10 -3 M) on the reaction of Eu(III) with polysilicic acid was negligible in the pH range 7.0 to 9.0. Dissolved Eu 3+ binds more strongly to the silicate polymers than do Cs + and Cu 2+ .

As part of the site characterisation program for the near surface radioactive waste treatment and disposal facility (RWTDF) at Püspökszilágy, Hungary, water quality and environmental isotope investigations have been carried out. Water samples for major ion chemistry, tritium, 14 C and stable isotope ratio measurements (δ 18 O, δ D , δ 34 S, δ 13 C) were taken quarterly from the observation wells, the streams and the precipitation during the period 1999–2001. The chemical composition of groundwaters presented a continuous transition from waters situated on one side to waters on the top and on the other slope of the disposal suggesting the mixing of the three hydrochemical “endmembers”. Most of δ D and δ 18 O data were situated between GMWL and LMWL (δ D = 7.2 × δ 18 O − 1‰) with Oligocene aquifer presenting recharge of Pleistocene origin and water on the top and the gentle slope of the hill presenting recharge of Holocene origin. δ 34 S values of dissolved sulphates varied in a wide range (-14.2‰ to + 5.4‰). The tritium in precipitation varied between 4.4 and 18.1 TU with an annual weighted average of 10 ± 0.3 TU. The streams showed larger fluctuations than the wells, but the changes of δ 18 O, δ D and T were small compared to those in precipitation (showing seasonal variation). Stable isotope, tritium and radiocarbon data proved that the replenishment of groundwater is slow on the steeper side and the direction of water movement is toward the gentle slope of the hill. It was judged that this path is the one that is most likely to give rise to high doses and, therefore, was used in the hydrological modelling of the safety assessment that followed the present work. The possibility that there may also be transport through the unsaturated zone and systems of perched water tables in layers 1 and 2 to both the Szilágyi and Némedi streams cannot be excluded; the transport along these pathways is likely to be intermittent.