Volume 95, Issue 7

In the framework of the French Environmental Nuclear Toxicology program, additional experiments related to the decorporation of actinides are planned. Decorporation is the removal or release from target organs (bones, liver, kidney …), tissues or cells of radioactive material previously incorporated in them, using chelating agents or other administrated pharmaceutical agents. The contradictory data on the neptunium complexation behaviour within blood and its transfer to target organs, as well as the inefficiency of therapeutic treatments, led us to study the complexation of this element with biological constituents. Within this purpose, the in vitro behaviour of Np(IV) and Np(V) in simple media simulating biological fluids was studied. This study was more specifically focused on the behaviour of neptunium with citrate ion, which is an essential component in a number of metalloenzyme active sites. In order to determine the speciation of this system, spectrophotometry was more particularly used. Concerning the complexation phenomenon, the existence of several complexes of Np(V) with various acido-basic forms of the citrate anion was observed; regarding Np(IV), complexes with Cit 3- have been observed. From the quantitative study of these equilibria, the values of the absolute constants for the complexation of Np(IV) and Np(V) with citrate were determined. Concerning the stability of neptunium towards oxydo-reduction, it was confirmed that Np(VI) was very quickly reduced to Np(V) by the citrate anions, whereas Np(IV) was stable. In the case of Np(V), it was observed that, depending on the pH and the citrate concentration, Np(V) was unstable and was reduced to Np(IV). The E –pH diagrams, constructed using the stability constants determined in this study, showed that this instability was due to the Np(V) disproportionation.

The solubility behaviour of a synthetic uranium(VI) oxide was studied under inert conditions in aqueous NaClO 4 solution at 25 ± 2 °C. The dissolution kinetics were investigated in respect of pH in solution and O 2 partial pressure in the atmosphere. The actual uranium concentration was determined by ICP-MS measurements. Under acidic conditions we observed a moderate solubility which increases by lowering of the pH of solution yielding to a solubility constant of log 10 K sp = −24.38 ± 0.07. The influence of the ionic strength, I , on the dissolution kinetics could be observed which was evaluated using a theoretical model considering the electrical double layer at the surface of the oxide as well as all possible reaction pathways. As a result we could determine the acid-base equilibrium constants of the surface groups and the overall reaction rate, k + , of dissolution process as a function of pH and I . On this basis we are able to determine the pzc of the uranium oxide, to be 7.28. It is in good accordance with a minimum in the tendency of the solid to dissolve which was observed in the pH range 6 to 8.

A 30% (w/w) N , N , N ′, N ′-tetraoctyldiglycol amide (TODGA) and 10% (w/w) tributyl-phosphate (TBP)-containing resin was prepared and the batch uptake of several actinides [U(VI), Th(IV), Am(III), Cm(III), Cf(III)] and selected fission products from nitric acid solutions was investigated. Two chromatographic column tests were carried out with a synthetic PUREX raffinate containing nominal amounts of fission products and trace amounts of Am(III), Cm(III) and Cf(III). The results of the separation experiments revealed that actinides and lanthanides could be separated from the bulk of other fission products by extraction chromatography using TODGA and TBP as the stationary phases.

The dissolution and electrochemical properties of molybdenum carbide were investigated using a number of electrochemical techniques, including general corrosion tests (GCT), linear voltammetry (LV), potential controlled electrolysis (PCE) and Scanning Electrochemical Microscopy (SECM), in basic media (0.5−4 M NaOH and 1 M NaHCO 3 /Na 2 CO 3 , pH 9.1–11.3). It was shown that the Mo 2 C corrosion potential ( E corr ) shifted towards negative values from -0.39 to -0.96 V/SCE with an increase of the OH - concentration and did not depend on the CO 3 2- concentration in the electrolyte. LV measurements in carbonate buffer (pH 9.2), evidenced three potential regions: passivation from E corr to -0.2 V/SCE, pseudopassivation from -0.25 to 0 V/SCE and anodic dissolution (transpassivation) at E > 0.1 V/SCE. The potentials delimiting the mentioned regions decreased with the increase of the OH - concentration, becoming undistinguished in 2 M NaOH. The Mo 2 C dissolution rate ( k diss ) in the transpassive state was estimated using LV data. In 4 M NaOH at -0.1 V/SCE, k diss reached 430 mg cm -2 h -1 and decreased with the decrease of the OH - concentration and the electrolysis potential. The Mo 2 C dissolution current efficiency varied between 12 and 13 F mol -1 Mo 2 C, proving the formation of the intermediate products of a carbon oxidative degradation during PCE. The presence of C 2 O 4 2- and non-identified aromatic compounds in the electrolytes after Mo 2 C dissolution was ascertained, using capillary zone electrophoresis. Scanning electrochemical microscopy (SECM) confirmed the formation of a pseudopassive film and demonstrated the increase of its thickness with the increase of the applied potential. The effect of the presence of Mo 2 C on the irradiated UC fuel dissolution rate and the mechanisms involved are discussed.

Hydrous titanium oxide was chemically synthesized and tested as adsorbent material for the removal of cesium, cobalt and strontium ions from chloride waste solutions using batch technique. The influences of pH, contact time, and temperature have been reported. The uptake of both strontium and cobalt ions was found to be greater than that of cesium and the apparent sorption capacity of each ion increases with increase in temperature. Thermodynamic parameters such as changes in Gibbs free energy (Δ G 0 ), enthalpy (Δ H 0 ), and entropy (Δ S 0 ) were calculated. The numerical value of Δ G 0 decreases with an increase in temperature, indicating that the sorption reaction of each ion was more favorable at higher temperature. The positive values of Δ H 0 correspond to the endothermic nature of sorption processes and suggested that chemisorption was the predominant mechanism. Analysis of the respective rate data in accordance with three kinetic models revealed that the homogeneous particle diffusion kinetic model was found to best correlate the experimental rate data. The numerical values of the rate constants and particle diffusion coefficients were determined from the graphical representation of the proposed models. The results indicated that prepared hydrous titanium oxide can be used as an efficient adsorbent material for the removal of strontium and cobalt ions from radioactive aqueous wastes.

So far, [carbonyl- 11 C]WAY-100635 is the PET-tracer of choice for 5HT 1A -receptor-imaging. Since the preparation is still a challenge, we aimed at (1) the evaluation of various essential parameters for the successful preparation, (2) the simplification of the radiosynthesis and (3) the establishment of a safe and fully automated system. The preparation is based on a commercial synthesizer and all chemicals are used without further processing. We found a low failure rate (7.7%), high average yield (4.0 ± 1.0 GBq) and a specific radioactivity of 292 ± 168 GBq/μmol (both at the end of synthesis, EOS).

The potential of Asclepias procera plant leaves as biomonitor for air pollution monitoring has been explored by analyzing 36 elements in the leaf samples employing Instrumental Neutron Activation Analysis (INAA) and Atomic Absorption Spectrometric (AAS) techniques. The leaf samples were collected in summer and winter seasons from urban areas of Islamabad with different anthropogenic activities as well as from a rural area as a reference site. The soil samples of the respective sites were also analyzed. The reliability of the methods used was established by analyzing the certified reference materials under identical experimental conditions and comparing the results obtained with the certified values, which are in quite good agreement with each other. Pollution Load Index (PLI) of the determined elements was computed and is discussed accordingly. The uptake of metals from soil to roots, stem and leaves has also been investigated by analyzing these parts of the same plant. The results suggest that the leaves of Asclepias procera plant have a good potential to indicate the air pollution levels both in the vicinity of industrial as well as near roadside areas.