Volume 91, Issue 10 -

A summary of methods for cyclotron production of 235 Np (396.1d), 236 Pu (2.858y) and 237 Pu (45.2d) via nuclear reactions with protons and 3 He-ions on 235,236,238 U and 237 Np targets in wide energy ranges is given. Methods for the chemical separation and purification of these nuclides from the irradiated uranium and neptunium targets are described. Cross sections, yields and radionuclidic purities of 235 Np, 236 Pu and 237 Pu are presented and compared with literature data on the nuclear reactions leading to these radionuclides. The nuclear reactions with the so far highest known yields of 235 Np, 236 Pu and 237 Pu are determined: 236 U( p ,2 n ) 235 Np, 237 Np( p ,2 n + pnβ - ) 236 Pu and 237 Np( p , n ) 237 Pu, respectively. The highest radionuclidic purity of 235 Np, 236 Pu and 237 Pu tracers can be reached with the 236 U( p ,2 n ) 235 Np, 236 U( p , nβ - ) 236 Pu and 237 Np( 3 He, t ) 237 Pu reactions, respectively. In addition new cross sections and yield data of the 236 U( 3 He, p 3 n ) 235 Np reaction in the energy range 42.4–60 MeV are given.

Humic acid metal ion interaction shows a complex kinetic behavior. Dissociation kinetics reported in the literature reach from hours to basically irreversibility. Different suggestions for the responsible mechanisms have been made. One possibility is variations in the metal ion humate complex environment, subject to this study. The dissociation kinetics of Eu(III)/Tb(III)/Cm(III) humate complexes is investigated with purified humic acid solution (Gohy-573(HA), pH=6.0, I =0.1M (NaClO 4 )) and a humic rich groundwater (Gohy-532, pH=7.5). The different kinetic modes are verified by both scavenging of dissociated metal ions by an cation exchanger added after different metal ion humic acid contact times, and isotope exchange under stationary conditions, i.e. without change in metal ion humic acid ratio. The metal ion humate complex environment is studied by time resolved laser-induced laser fluorescence spectroscopy (TRLFS) and EXAFS. TRLFS shows that slower dissociating Cm(III) humate has a peak maximum at 600.5nm contrary to the fast dissociating ones with a peak maximum around 602.8nm. EXAFS also shows differences between slow and fast dissociating complexes (Tb(III), with an average Tb(III) oxygen distance of 2.37Å for an equilibrium mixture, and 2.33Å for only the slow dissociating complex. TRLFS shows that complexes with fast and slow dissociation kinetics have returned to the original distribution three days after removal of the fast dissociating metal ions and thus the different kinetic modes are in exchange equilibrium with each other. Furthermore, the isotope exchange investigations verify that humic acid europium flocculate basically behaves like dissolved/dispersed humate complexes.

The sorption and desorption isotherms and the corresponding distribution coefficients ( K d , mL/g) of Np(V) for untreated loess and three kinds of treated loesses were determined by using the batch technique at moderate concentrations (∼10 -5 mol/L) under ambient aerobic conditions in the presence of 0.01mol/L CaCl 2 . For the treated loesses, selective extraction methods were used to remove CaCO 3 and organic matter (OM) from the loess. The isotherms were analyzed with the Freundlich equation. The relative contributions of OM and CaCO 3 to the Np(V) sorption on the loess were investigated from the parameters of the Freundlich equation. The effects of adding fulvic acid (FA) from the loess and the carbonate in solution on the sorption of neptunium(V) on the loess were studied. The breakthrough curves (BTCs) and displacement curves (DPCs) of Np(V) on the untreated loess column and on the treated loess columns were determined under ambient aerobic conditions at moderate concentration (1.1×10 -4 mol/L) in the presence of 0.01mol/L CaCl 2 . The results of column experiments are in accord with the results of batch experiments. It was found that (1) Np(V) in the loess under the present experimental conditions was relatively mobile and the distribution coefficients were relatively low at moderate concentrations, (2) the sorption/desorption hysteresis of Np(V) on the loess occurs, (3) the sorption of Np(V) on the loess was mainly determined by the clay minerals, (4) the addition of FA or carbonate in the aqueous solutions had an obvious positive effect on the Np(V) sorption on the loess, (5) the retardation of Np(V) migration in the loess at moderate concentrations was inconsiderable.

We used a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray (EDX) analysis to conduct molecular scale studies on U(VI) interaction with three recently described eco-types of Acidithiobacillus ferrooxidans . On the basis of the information obtained by using these methods, we concluded that uranyl phosphate complexes were formed by the cells of the three eco-types studied. The uranium accumulated by A. ferrooxidans cells was located mainly within the extracellular polysaccharides, and on the cell wall. Smaller amounts were also observed in the cytoplasm.

The extraction behaviour of U (VI) from an aqueous nitric acid medium employing a 2-hydroxy-1-naphthaldehyde thiosemicarbazone in ethyl acetate has been studied in presence of different neutral donors like trioctyl phosphine oxide (TOPO), dimethyl sulphoxide (DMSO) and trioctyl amine (TOA). The extraction constant (log k ex ) for the binary organic phases UO 2 ·A·X (where A=ligand, X=NO 3 -1 ) was found to be 1.976 which is by far the largest value amongst known values for the thiosemicarbazone. The overall equilibrium constant (log K ) for the ternary complexes UO 2 A(NO 3 )·TOPO, UO 2 A(NO 3 )·TOA and UO 2 A(NO 3 )·DMSO were estimated to be 6.06, 6.77 and 4.95, respectively. The effect of different diluents on the extraction behaviour has also been studied.

An electromigration technique was used for measurements of metal-ligand formation constants of non-carrier-free 160 Tb 3+ with glycolate, D -gluconate and α -isosaccharinate ligands. The overall ion mobilities of Tb at different concentrations of the ligands were measured in chemically inert perchlorate solutions (pH 7 and T = 298.1K) with an overall ionic strength μ = 0.1. The stepwise stoichiometric stability constants are: Tb 3+ /glycolate: log K 1 =2.72(18), log K 2 =1.73(19), log K 3 = 1.12(17), Tb 3+ / D -gluconate: log K 1 =2.96(11), log K 2 =2.60(11), log K 3 =1.13(9), Tb 3+ / α -ISA: log K 1 =3.07(8), log K 2 = 2.69(11), log K 3 = 1.80(12).

Two types of hydrous titanium dioxide possessing different surface properties were prepared and characterized to study the sorption kinetics of cesium. The effect of pH on the adsorption capacity were determined in both type sorbents and the maximum adsorption percentage of cesium were observed at pH 12. To elucidate the kinetics of ion-exchange reaction on hydrous titanium dioxide, the isotopic exchange rates of cesium ions between hydrous titanium dioxides and aqueous solutions were measured radiochemically and compared with each other. The diffusion coefficients of Cs + ion for Type1 and Type2 titanium dioxides at pH 12 were calculated as 2.79×10 -11 m 2 s -1 and 1.52×10 -11 m 2 s -1 , respectively, under particle diffusion controlled conditions.

MDP (methylenediphosphonate) and HEDP (hydroxyethylidene diphosphonate), both diphosphonates, and EDTMP (ethylenediamine tetramethylene phosphonic acid), a tetraphosphonate ligand, have been previously labeled with 188 Re for use in metastatic bone-pain palliation. The aim of this study was a comparison between the three complexes 188 Re-MDP, 188 Re-HEDP and 188 Re-EDTMP concerning the complexation conditions, in order to achieve maximum yield, stability and bone uptake. Methods: MDP was dissolved in water and HEDP and EDTMP were dissolved in NaOH 1N followed by reduction of pH with HCl 1N. To all mixtures stannous chloride and 188 Re 4 - were added in a nitrogen atmosphere. The preparations were heated in boiling water bath for 15min. Yield as well as radiochemical stability was estimated by ITLC. Different concentrations of phosphonates and stannous chloride were evaluated. Biodistribution studies in Swiss mice were done for the three 188 Re-phosphonates that presented the best radiochemical yield. The optimal ligand concentration for maximum complexation was 85.2mM for MDP, 72.8mM for HEDP and 45.8mM for EDTMP. The best amount of SnCl 2 ·2H 2 O} was 1.5mg/mL for 188 Re-HEDP and 1mg/mL for both 188 Re-MDP and 188 Re-EDTMP. In these conditons the three complexes showed a complexation rate above 95. Reasonable radiochemical stability for 24 hours was achieved by 188 Re-EDTMP when employing ascorbic acid. All products showed a great uptake by the kidneys. 188 Re-EDTMP had the greatest uptake by femur (3.1±0.2 ID/g) followed by 188 Re-MDP (1.2±0.1 ID/g) and 188 Re-HEDP (1.0±0.1 ID/g), 4 hours post injection. 188 Re-EDTMP displayed a femur bone/muscle ratio of 28.5, 188 Re-MDP 4.9 and 188 Re-HEDP 4.9. In conclusion 188 Re-EDTMP demonstrated the best potential as a radiopharmaceutical for bone cancer pain relief, encouraging further dosimetric studies and clinical trials.

The radionuclide Tc-94m with its positron branching ratio of 72, positron end-point energy of 2.47MeV, and relatively short half-life of 52 minutes is suitable for quantitative measurements using PET. Tc-94m can be produced by proton bombardment of isotopically enriched [Mo-94]MoO 3 . We prepare Tc-94m as pertechnetate in saline solution using a wet-chemical separation procedure employing a semi-automated apparatus. Tc-94m sestamibi and other radiopharmaceuticals are routinely produced from this reagent.