Band 98, Heft 7 -

186 Re is an important radionuclide having a half-life of 3.72 d that is suitable for radioimmunotherapy. Its production in no-carrier-added form is done via charged particle induced reactions and the data are available in EXFOR library. We evaluated two charged particle induced reactions, namely 186 W( p , n ) 186 Re and 186 W( d ,2 n ) 186 Re. In the first case, analysis was done up to about 70 MeV but in the latter only up to about 50 MeV. A statistical procedure supported by nuclear model calculations using the codes STAPRE, EMPIRE and TALYS was used to validate and fit the data. The recommended sets of data derived together with 95% confidence limits are reported. The application of those data, particularly in the calculation of integral yields is discussed. The 186 W( p , n ) 186 Re reaction on highly enriched 186 W is presently the method of choice for production of no-carrier-added 186 Re and, taking into account the radionuclidic purity, the maximum recommended proton energy is 18 MeV. The formation of the very long-lived isomer, 186m Re, is briefly discussed. The 186 W( d ,2 n ) 186 Re reaction could also be interesting if a high-intensity accelerator would be available.

Using cyclic voltammetry, we investigated the redox behavior of Ce(IV)/Ce(III), which is a surrogate for An(IV)/An(III) (An=actinides), in a solution of nitrilotriacetic acid (NTA) at 25 °C. The cyclic voltammogram of Ce in a 0.1 M NTA solution at pH 6 showed a reversible one-electron redox reaction for Ce(IV)/Ce(III) at 0.51 V vs. Ag/AgCl. This redox potential was much lower than that obtained in 1 M nitric acid, indicating that Ce(IV) was preferentially stabilized by complexation with NTA. The redox potential in the NTA solution was independent of the Ce concentration from 2 to 20 mM, NTA concentration from 5 to 200 mM and pH between 3 and 7. These results indicated that no polymerization and no additional coordination of NTA and OH − to the Ce(III)-NTA complex took place during the redox reaction. As the speciation calculation of Ce(III) in the NTA solution showed that the predominant species was Ce III (nta) 2 3− (H 3 nta=NTA), the redox reaction of the Ce-NTA complex was expressed by the following: Ce IV (nta) 2 2− +e − ⇋Ce III (nta) 2 3− . The logarithm of the stability constant of Ce IV (nta) 2 2− was calculated to be 38.6±0.8 for I =0 from the redox potential shift of Ce(IV)/Ce(III) in the NTA solution. The value was in good accordance with the stability constant of the Np IV (nta) 2 2− complex, demonstrating that the aqueous coordination chemistry of Ce(IV) with NTA is quite similar to that of An(IV). These results strongly suggest that a negative shift of the Pu(IV)/Pu(III) redox potential in the NTA solution should make Pu(IV) more stable than Pu(III) even in a reducing environment.

Supercritical carbon dioxide (SC CO 2 ) extraction of uranium from nitric acid medium employing various crown ethers was studied. CO 2 -phillic C–F bonds in pentadecafluoro- n -octanic acid (HPFOA) counter ion enhanced the extraction efficiency. Pressure (100−300 atm) and temperature (323−353 K) were found to influence extraction efficiency by affecting SC CO 2 density as well as due to large size cluster formation of supercritical fluid near critical point thereby resulting in reduced interaction with solute. Pressure of 200 atm and temperature of 323 K were found to be optimum. The trend in efficiency for benzo substituted crown ethers was due to the combined effect of cavity size and number of ether oxygen atoms. The extraction efficiency among 18-crown-6 series is influenced by the extent of basicity of ether oxygen, which in turn is dictated by the substituent group. Efficiency also decreased beyond 2 M nitric acid due to co-extraction of crown-nitric acid complex. Uranium: crown: HPFOA mole ratio influenced extraction efficiency, having optimum value at 1:10:100. Under optimized conditions with ditertiarybutyldicyclohexano-18-crown-6 the efficiency was found to be (86±5) %.

The purpose of the work was to improve the process for treatment of liquid radioactive waste containing complexing agents, which are generated during the decontamination operations. We performed some experiments using simulated waste solutions like secondary waste from the modified CANDEREM process (Canadian Decontamination and Remediation Process) and secondary waste from the modified CANDECON process (Canadian Decontamination Process). To improve efficiency and economics of the process it was proposed to treat the waste by combining the sorption of radionuclides on natural inorganic sorbents (zeolites) with membrane filtration. Standard procedures are applied to compare the sorption of radionuclides on different sorbent forms-determination of the ion exchange capacity, construction of sorption isotherms, determination of the distribution coefficients, and kinetics experiments. To check the influence of converting the sorbents to various cationic forms on their sorption properties, distribution coefficients of 137 Cs and 57 Co on natural zeolites from local deposits converted to NH 4 + , Na + or H + forms were determined. The results obtained show that the distribution coefficients of 137 Cs on the materials converted to Na + form are higher than for the remaining forms studied [1]. The parameters of Langmuir, Freundlich and Dubinin–Radushkevich adsorption isotherms have been determined using sorption data. The Dubinin–Radushkevich model shows better correlation between the theoretical and experimental data for 137 Cs sorption on natural zeolites from local deposits converted to NH 4 + and H + forms than Langmuir and Freundlich equations. Kinetic studies were carried out with various zeolite forms. The sorbents studied are natural zeolites from local deposits (Marsid-Romania). The batch sorption kinetics has been tested for pseudo-second order reaction. The pseudo-second order model fits the experimental data well for all of the systems studied.

The surface charge characteristics of Na-rectorite (NaAl 4 [Si,Al] 8 O 20 (OH) 4 · n H 2 O) were studied by potentiometric acid-base titrations. Sr(II) and Eu(III) adsorptions on Na-rectorite as a function of pH, ionic strength, and Sr(II)/Eu(III) concentrations were carried out to investigate the surface interactions between Sr(II)/Eu(III) with Na-rectorite. The results indicated that the adsorptions of Sr(II) and Eu(III) on Na-rectorite increased with increasing pH and decreased with increasing ionic strength and initial Sr(II)/Eu(III) concentrations, and that the affinity of Na-rectorite for Eu(III) was much higher than for Sr(II). The experimental data of Sr(II)/Eu(III) adsorption were simulated by the diffuse-layer model (DLM) well with the aid of FITEQL 3.2. Simultaneous adsorptions of Sr(II) and Eu(III) on Na-rectorite were also modeled using the DLM. The adsorption mechanisms of Sr(II) and Eu(III) on Na-rectorite may be dominated by ion exchange interaction at low pH or moderate pH, and by surface complexation interaction at high pH.

The ion adsorption properties of muscovite mica were exploited to prepare higher resolution alpha-spectroscopy samples of 242 Pu. The samples prepared by our method are compared to those prepared using electrodeposition methods in terms of their energy resolution. The mica adsorption method results in significant increases in energy resolution vs. that of electrodeposition. Muscovite surface adsorption properties of the mica allow for monolayer adsorption of plutonium thus minimizing energy attenuation and maximizing energy resolution of the resulting spectra. The mica adsorption method allows for simplified preparation of higher-resolution alpha-spectroscopy samples useful for the isotopic analysis of alpha-emitting radionuclides.

A method is described for separating radioyttrium from strontium within 30−40 min. The yield of radioyttrium amounts to 97% and the strontium impurity occurs at 8.2 ppm level. Radioyttrium (containing 86 Y, 87 Y and 88 Y) was produced by proton-induced nuclear reactions on nat SrCO 3 deposited on Cu backing. Irradiated target material was removed with acetone and 8 M HCl solution from copper substrate, followed by ethyl cellulose (EC) filter removal. Optimal radioyttrium separations from Cu and 65 Zn activities were obtained by loading the mixture on Dowex-1×8 anion exchange resin and eluting with 8 M HCl, followed by precipitation of nat Sr as SrSO 4 while radioyttrium passed through the filter paper.

Selected trace and minor elements analyzed by XRF in sandstone samples were Rb-Sr-Zr-Nb-Ba-La-Ce-Nd as well as Ti-Mn-Fe with which they are often correlated. Refractory elements like REE are considered useful indicators of geochemical processes and, in this case, of provenance . Usually they maintain their original relationships and are transferred almost directly into sediments. The values here found, absolute and normalized, show correlations among the samples, allowing the establishment of their origin. Most of them in the spidergram patterns display positive spikes of Zr, and negative anomalies at Nb, Sr, Ti: differences in their height/depth could be in relation with the different Series or Formations. Strikingly, spidergrams of samples collected from the Patiño Formation show marked negative anomalies interalia of Ba, as well as positive spikes of Nb and Zr, very similar to those found in magmatic specimens from Misiones, Carapeguá-Acahay and Alto Paraguay Province and quite different from the other analyzed samples. In addition a remarkable presence of Precambrian signatures were found in the analyzed sandstones from the Paleozoic.