Volume 90, Issue 5 -

The partial alpha emitting lanthanide isotope 149 Tb seems to have a great potential in systemic radioimmuno therapy (RIT), especially when single cells in transit or circulation are targeted. The isotope 149 Tb has a half life of 4.118 h and decays by alpha emission (3.97 MeV, 17%) EC-process (76%) and β + -emission (7%). In this paper, we analyze the possible production routes: light- and heavy ion induced nuclear reactions and p-induced spallation. The excitation functions for light- and heavy ion induced reactions have been calculated using the ALICE91 code. The direct nuclear reaction 152 Gd ( p , 4 n ) 149 Tb was found to be the most promising production path. Alternatively, the indirect reaction 142 Nd ( 12 C, 5 n ) 149 Dy → 149 Tb seems to be much more suitable compared to the reaction on the mono-isotopic target element 141 Pr 12 C, 4 n ) 149 Tb. In this case, both, the production yield of 149 Tb and the radionuclidic purity are considerably lower, compared to the ( p , 4 n )-reaction. In preliminary experiments we produced 149 Tb via the indirect reaction Nd ( 12 C, 5 n ) 149 Dy → 149 Tb (108 MeV 12 C +6 ions and 1 particle-µA) at the U-200 heavy ion cyclotron at the FLNR of the JINR Dubna. From a 1.25 h irradiation of a 12 mg/cm 2 nat Nd 2 O 3 target, we obtained 2.7 MBq of 149 Tb (70 µCi) at 20 min EOB. This allows the conclusion, that a dedicated cyclotron equipped with a modern ECR-ion source, providing high ion currents would allow the continuous production of batches of the order of 10–20 GBq of 149 Tb for routine RI-therapy. The lower cross section of the spallation process can be compensated by using very thick targets. On-line mass separation technique provides high purity isotopically clean 149 Tb preparations, independently on the production route chosen. At the ISOLDE facility at CERN, we prepared batches of up to 500 MBq 149 Tb by combining on-line mass separation process followed by a cation exchange chromatography process using α-HIBA as eluent. The obtained 149 Tb preparations showed excellent behavior in labeling of chelated monoclonal antibodies.

Americium exhibits a soluble form in aqueous alkaline media in the presence of ferricyanide ions (Fe(CN) 6 3− ), which is not the case for the other transplutonium elements (TPE). This soluble Am compound can be obtained by addition of a concentrated basic solution of ferricyanide ions on a trivalent americium hydroxide precipitate. Thus, this technique enables a complete and rapid extraction of americium through its soluble form in alkaline solutions whereas under these conditions, other TPE and the lanthanides remain in the solid state as trivalent hydroxides. In the case of dissolution involving large amounts of americium, the formation of the soluble americium species is followed by the appearance of a reddish precipitate in the basic solution. Dissolution of the reddish solid in NaOH or NaOH/Fe(CN) 6 3− media demonstrated the existence of a media-dependent solubility of the precipitate, and therefore the existence of at least two forms of soluble Am. Spectroscopic (UV-visible, EXAFS-XANES, Raman) and electrochemical investigations were carried out on the different forms of americium to determine the nature of the compounds. This study points out that the reddish solid Am compound is probably a Am(V) hydroxide: Na 2 AmO 2 (OH) 3 ·3H 2 O while the other Am species is a mixed americyl–ferricyanide complex. This work demonstrates that this dissolution of Am(III) solid compound is much more complex than a simple oxidation by the ferricyanide ions. The existence of a molecular interaction between Am(V)O 2 + and ferricyanide ions is highly probable. This selective dissolution of americium by a basic ferricyanide solution can be used to define a separation process of Am from lanthanides and other transplutonium elements in the field of high level liquid waste treatment.

The rapid reduction of NpO 2 2+ ions to NpO 2 + by U(IV) ions in an aqueous nitric acid solution has been studied and, in many ways, is similar in character to the same reaction in HClO 4 . The major difference is that in HNO 3 the reaction proceeds via two parallel routes. The first is via the hydrolysed UOH 3+ ion, as in the reaction in HClO 4 and the second is via the non-hydrolysed U 4+ ion. These parallel routes lead to the observed order of reaction with respect to H + ions being reduced from −1 in HClO 4 to −0.7 in HNO 3 . After accounting for the reaction mechanism the rate equation is described by: where k 8 = 404 min −1 , k 19 = 275 M −1 min −1 and β = 0.009 M at 10 °C and μ = 2. The activation energy was 66.5 ± 4.9 kJ mol −1 . Nitrate ions had no effect on the reaction rate but sulphamic acid increased the observed rate, probably through catalysis by sulphate ions arising from sulphamic acid reaction with HNO 2 and hydrolysis.

237 Np is a long-lived actinide (2.14 × 10 6 y), an α emitter, which is present either in the fuel cycle or in the environment as a result of local fallout. Due to the low concentration level encountered in bioassays or environmental samples, a preconcentration is necessary and several analytical tools can be used, namely: α-spectrometry, PERALS (Photon Electron Rejecting Alpha Liquid Scintillation) or ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). In the case of actinide mixtures where interference can occur, a radiochemical separation is necessary prior to measurement in order to obtain a pure fraction of each actinide. In this paper different approaches, still in use for actinide mixtures and based on ion exchange, extraction chromatography and solvent extraction, are investigated and compared for 237 Np analysis on synthetic solutions. In addition, the suitability of the various procedures is discussed for Np regarding several criteria such as the constraints of the analytical tool, the concentration level, the time needed for the analysis and waste generation.

A simple method of preparing α-sources for alpha spectrometric analysis of uranium and thorium is investigated by combining solvent extraction and electrodeposition procedures. Extraction of these actinides is performed by diethyl ether from calcium nitrate solution with various nitric acid concentrations. Recoveries of 90–100% are obtained for uranium and 83.5% for thorium. Good resolutions are also achieved under optimum conditions. The dependence of the overall yield of U(VI) and Th(IV) is examined in relation to the aqueous phase acidity. A procedure combining solvent extraction and electrodeposition is proposed for a selective α-source preparation of U(VI) and Th(IV). Uranium is first extracted at pH range about 1 to 2. At this acidity, thorium remains in the aqueous phase and may be subsequently extracted from this after acidification with 2 M HNO 3 . A second decontamination of a specific nuclide is achieved by a selective electrodeposition using electrolyte consisting of about 70% ethanol, 0.45 M hydrochloric acid, 0.09 M acetic acid and 108 µg Fe 2 O 3 , with concentrations above 0.48 M in HCl for U(VI) or 0.06 to 0.09 M in HNO 3 for Th(IV).

We propose a new fully aqueous electrochemical method for the preparation of high resolution alpha sources. Thin films of polypyrrole (PPy) are prepared by anodic electropolymerization, starting from aqueous solutions of the pyrrole monomer and an anionic polyelectrolyte which is able to complex actinide and play the role of PPy doping agent: polyacrylamidoglycolic acid (PAGA). These thin films can be prepared on various electrodes: stainless steel, platinum, glassy carbon and polyethylene doped by carbon-black. Peeling tests revealed their strong adhesion on stainless steel electrode. Alpha sources were prepared by simple immersion in actinide containing solutions. This easy process results in alpha sources with outstanding energy resolution (FWHM: around 9 keV for various isotopes).

Ammonium molybdophosphate(AMP) was synthesized and characterized. The AMP was found to be insoluble in water or nitric acid solutions of different concentrations. The sorption of Th and U from nitric acid by AMP has been investigated. The effect of shaking time on the sorption of Th was studied. The effect of nitric acid, Th concentration and AMP on the sorption of Th were also studied. Studies on the retention capacity of AMP showed that its capacity decreased by increasing the nitric acid concentration of Th. The saturation capacity was found to be 120 mg Th/g AMP from 0.1 M HNO 3 , 80 mg Th/g AMP from 3 M HNO 3 . On the basis of these results a selective and new method for separating of Th from U was developed using a floating bed column.

The complexation behavior of europium(III) with polymaleic acid (PMA) was studied at pH 5 in 0.1 M NaClO 4 by anion exchange (AE). The concentration range investigated was from E-9 M to E-4 M for the europium ion and from 1 to 50 mg/l for the polymer. The quantitative description of experimental data showed the formation of a 1 : 1 Eu : PMA complex and the existence of at least two distinct interaction environments ("sites") of Eu with the polymer chain whose proportions varied with the ratio between total Eu and PMA concentrations. The existence of different sites was further demonstrated by Time Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) measuring the lifetimes and emission spectra of EuPMA complexes. By using empirical relationships, environments implying 1 : 2 and 1 : 1 Eu : COO − coordination could be deduced. The results show similarities with published data obtained for fulvic and Aldrich humic acids as far as complexation properties at pH = 5 are concerned.

A liquid-liquid extraction method has been investigated for quantitative extraction of hafnium from 8 M HNO 3 using 50% di- n -butyl sulfoxide (DBSO) dissolved in cyclohexane. The extraction parameters such as nitric acid, DBSO and metal ion concentrations, equilibration time and temperature were optimized. The extraction was found to be independent of metal ion concentration in the range 4.5 × 10 −4 −4.5 × 10 −2 M and inversely dependent upon the temperature. Phosphate, fluoride and oxalate interfere seriously and have almost masked the extraction of Hf(IV) whereas, thiocyanate and bromide have greatly decreased (25–34%) the extraction. The stoichiometric composition of the extracted species was found to be Hf(NO 3 ) 4 ·2DBSO. Hafnium can be stripped from the organic phase by using 1 M HClO 4 . The proposed method allows the mutual separation of Hf(IV) and Zr(IV) using H 2 O 2 as masking agent for zirconium. The method has also been applied on synthetic mixtures of Hf and Zr for their separation and, the recovery was found to be quantitative.

Irrespective of low bioavailability, some plant species accumulate Y and rare earth elements (REEs) to a great extent (accumulator species). The uptake mechanisms of Y and REEs were investigated for autumn fern, one of accumulator species. For comparison, plant species which accumulated poorly REEs (non-accumulator species) were also studied. In the present investigation, two noticeable phenomena were observed. (I) Autumn fern showed no ionic-radius dependence of Y-REE uptake by leaves, while non-accumulator species showed an extremely high uptake for Y compared with REEs. (II) Y-REE uptake by autumn fern was influenced by the addition of chelating reagents to the uptake solution, while no effect was observed for non-accumulator species.