Band 89, Heft 2 -

With the aim of preparing carrier-free 28 Mg and 47 Ca simultaneously, Ti, V and Fe targets were examined by irradiating with high-energy ions of 12 C, 14 N and 16 O accelerated by the RIKEN Ring Cyclotron. Among the targets, V gave the highest cross section for the formation of both 28 Mg and 47 Ca irrespective of the kind of beams. The cross section for the formation of 28 Mg by the reactions of Ti, V and Fe targets with ion beams increased in the order of 12 C < 16 O< 14 N. On the other hand, the three beams exhibited almost the same cross sections for the formation of 47 Ca by the reaction of a given target. Titanium and V were selected as prospective targets and 14 N as a suitable beam for the production of 28 Mg and 47 Ca. Chemical separation procedures of the radiotracers in carrier- and salt-free states have been established by using cation exchange resins. The recovery yields of 28 Mg and 47 Ca from Ti target were 70 and 90%, respectively, and the decontamination factor was less than 10 -5 . The recovery yields of 28 Mg and 47 Ca from V target were 80% and the decontamination factor was less than 10 -7 .

The solubility of PuO 2 (am) was determined in the aqueous Na + H + -OH - -Cl - -H 2 O-ethylenediaminetetraacetate (EDTA) system as a function of pH (1 to 13.5) and EDTA concentrations (0.00001 to 0.093 M) to determine PuEDTA complexes important in a wide range of pH values and EDTA concentrations. The solubility studies were carried out as a function of time and show, as expected, that steady-state/equilibrium in this system is reached rapidly (<7 days). The aqueous Pu oxidation states were determined by X-ray absorption near edge spectroscopy and solvent extraction. The aqueous Pu(IV) concentrations in equilibrium with PuO 2 (am) at fixed concentrations of EDTA (0.0001 or 0.001;M) as a function of pH, and at fixed pH (∼9), and as a function of EDTA were interpreted using the Pitzer ion-interaction model. The model was developed based on a subset of the experimental data and was validated against the remaining, more extensive data not used in model development. The log K 0 values for the formation of Pu(OH) x EDTA x- according to the generalized reaction (Pu 4+ + xOH +EDTA 4- ↔ Pu(OH) x EDTA -x ) were determined to be 36.44±0.35, 44.78±0.35, and 49.80±0.35 for x=1, 2, and 3, respectively, when log;K 0 of -56.85 for (PuO 2 (am)+2H 2 O harr; Pu 4+ +4OH - ) is used.

The oxidation of U(IV) to U(VI) with molecular oxygen in acidic aqueous NaClO 4 (I=0.5 M) solutions at different temperatures was studied. It was found that the reaction kinetics is a combination of a first-order reaction and an autocatalytic reaction. The speciation of tetravalent uranium is important since it was found that the two first hydrolysed uranium(IV) species are the reactive species under the conditions studied. One problem in interpreting the results comes from the lack of thermodynamic data. However, oxidation kinetic experiments may be a method for determining stability constants for redox sensitive tetravalent actinides. The stability constants for the formation of the first two hydrolysed complexes of U(IV) are reported in this work, e.g. log * β 1 (I = 0.5;M, T = 303.15;K)= 1.39±0.42, as compared to the literature value of -1.39±0.20.

Time-Resolved Laser-induced Fluorescence spectroscopy (TRLFS) is used to study the properties of excited UO 2 2+ ions (fluorescence lifetimes and emission spectra) in the presence of perchlorate ions (up to 5.5 M concentration). The experiments are performed at three perchloric acid concentrations (0.2, 1 and 2 M). Although ClO 4 - is known not to complex with UO 2 2+ , increasing amounts of ClO 4 - lead to a decrease of the lifetime for each [H + ] series. The emission spectra do not show any spectral shift and the fluorescence intensity is well correlated with the lifetime variation. Three different models are discussed to interpret the data: (a) A model based on the assumption of a chemical equilibrium between UO 2 2+ and ClO 4 - , both in their ground states. (b) A model which additionally takes into account excited state reactions of UO 2 2+ . (c) A third model which is solely based on photochemical, excited state reactions of UO 2 2+ . It is the only one consistent with the present data and results of other studies of the uranium(VI)/perchlorate system. Hence, photochemical reactions, even in the presence of weakly or non-complexing ligands like perchlorate ions, need to be taken into account in TRLFS experiments.

Liquid-liquid extraction studies of plutonium and americium from aqueous carbonate medium using a high molecular weight carboxylic acid namely cekanoic acid in different diluents has been carried out. The distribution ratio (D) values for Pu(IV) and Am(III) under various parameters such as concentration of extractant, Na 2 CO 3 and initial pH were obtained. Results indicated that Pu(IV) and Am(III) could be satisfactorily extracted together or individually from aqueous carbonate medium using cekanoic acid in different diluents like carbon tetrachloride, cyclohexane, toluene, n-dodecane or solvesso-100. The D values for Pu(IV) and Am(III) also indicated the possibility of their mutual separation. The back extraction of Pu and Am with different reagents was also studied.

A Mössbauer effect method was used to study the formation of mixed hydroxides in the alkaline coprecipitation of Pu(IV) or Np(IV) with Fe(III). The Mössbauer spectra of mixed 239 Pu(IV)-Fe(III) and 237 Np(IV)-Fe(III) hydroxide samples differ from that of pure α-FeO(OH) formed in aqueous basic solutions. Alkaline coprecipitation of Np(V) or Np(VI) with Fe(III) hydroxides does not produce the mixed hydroxides shown by Pu(IV) or Np(IV) with Fe(III). The general Mössbauer spectral parameters of the Np(V),(VI)-Fe(III) hydroxides are similar to those of pure α-FeO(OH).

Using a multitracer technique, the effects of acid rain pH on the adsorption of 15 trace elements on soil were studied. Kaolin, forest soil (original and with partially removed oxides), black soil (original and without organic matter)and Kureha soil (original, with partially removed oxides, and without organic matter) were employed as the adsorbents. Instead of H 2 SO 4 solution, HCl solution was selected as the model acid rain based on the results of adsorption experiments on kaolin. In general, the percentage adsorption of cationic elements on three original soils and kaolin increased with increasing pH. The adsorption of oxyanionic elements, As and Se, on three soils was high over the entire pH range studied, while that on kaolin was low and decreased with an increase in pH. The differences in the physical and chemical properties of soils were reflected on the adsorption. The organicmatter in soil had positive effects on the extent of adsorption of most elements studied, while the oxides apparently showed positive effects only for Fe and Se adsorption. The results indicate that acid rain decreases the retention of cations in soil and that it increases or does not change the adsorption of anions.

Iodide ions I - , molecular iodine I 2 and iodate ions IO 3 - absorption has been studied on the three alloys which are present, in majority, in french nuclear reactors: Inconel 600, Zircaloy and 304L stainless steel. Iodide and iodate anions are not absorbed on the three considered alloys and contribute only for a negligible quantity to iodine retention on the nuclear reactors materials. Molecular iodine is absorbed according to: 304 stainless steel < Zircaloy < Inconel 600. Influence of pH has been studied: absorption increases in acidic medium and decreases in basic medium. Molecular iodine absorption increases with temperature.Phenomenons which occur with iodine during the cold shutdown of a nuclear reactor and during its restart are discussed from the point of vue of iodine volatilization risk.

Pentavalent rhenium-188 dimercaptosuccinic acid [ 188 Re(V)DMSA] is a β-emitting radiopharmaceutical that has been proposed for the treatment of painful bone metastases, medullary thyroid carcinoma and other soft tissue tumours. In this study the development of a kit formulation for convenient, routine preparation of 188 Re(V)DMSA is presented. The kit contains all the ingredients in a single vial and its reconstitution with 188 Re perrhenate, up to 4;mL, produces 188 Re(V)DMSA in high radiochemical purity, suitable for clinical application. 188 Re(V)DMSA prepared by this kit method was evaluated in mice and resulted in a biodistribution pattern similar to that of 99m Tc(V)DMSA.

Positron annihilation lifetime (PAL) spectroscopy has been applied to polyvinyl alcohol (PVA) films prepared with commercially available PVA or from polyvinyl acetate (PVAc). The variation of lifetimes of ortho-positronium (o-Ps) formed in the films was investigated as a function of the degrees of polymerization, saponification, or crystallinity. For the fully saponificated samples, no dependence was found to exist on the degrees of polymerization or of crystallinity. For the partially saponificated samples, however, the dependence of the o-Ps lifetime on the degree of saponification was clearly observed, and this is explained by both the formation of hydrogen bonds among the polymer chains and the existence of acetyl group strongly inhibiting the hydrogen-bond formation due to steric hindrance.