Band 94, Heft 12

Excitation functions of proton induced reactions on nat Ti, leading to the formation of 43,44m,44g,47 Sc and 48 V, were measured using the stacked-foil technique over the proton energies starting from the respective reaction threshold up to 27.5 MeV. The new experimental values were compared with earlier reported data. In general good agreement was found. Also in the case of 48 V the results were compared with the cross-section values recommended by the International Atomic Energy Agency. A good agreement was observed.

Accelerator mass spectrometry (AMS) was applied to the analysis of 36 Cl induced in concrete samples obtained from accelerator facilities. In order to use a small amount of concrete sample and to separate chlorine as pure as possible, an improvement of separation process was developped. Chlorine was extracted from 1–5 g of concrete into 0.01 M nitric acid in a pressurized decomposition vessel. After determining chlorine using ion chromatography, a certain amount of NaCl solution was added to obtain sufficient amounts of AgCl precipitate and to dilute to a suitable isotope ratio of 36 Cl to 35 Cl ( 36 Cl/ 35 Cl) for the AMS (10 -12 –10 -10 ). A careful purification procedure was applied to reduce 36 S interference in AMS. Good reproducibility and small error throughout the chemical process for sample preparation was attained. Depth profiles of 36 Cl/ 35 Cl in concrete of a medium-energy cyclotron were measured by the developed method and compared with the results of γ-emitters induced by thermal neutrons. Since it was confirmed that 36 Cl was produced by thermal neutron capture of 35 Cl, the thermal neutron fluence irradiated during accelerator operation could be obtained using 36 Cl/ 35 Cl. In order to estimate the neutron fluences, the 36 Cl/ 35 Cl measurement by AMS is more useful than radioactivity measurements of other isotopes such as γ-emitters because AMS directly provides the isotope ratio and the half-life of 36 Cl is very long.

Removal of radioactive nuclides from effluents is important for the safe disposal of the radioactive waste. In the present work ion exchange studies were carried out using simulated alpha active organic liquid scintillator and ethyl alcohol waste solutions containing Pu and Am using different resins. The time of equilibration and batch data were obtained under different conditions for individual resins as well as their mixtures. The indigenously developed Macroporous bifunctional phosphinic acid (MPBPA) resin was found to be suitable for the removal of alpha activity mainly due to Pu and Amberlite IR-120 and Biorad 50W × 8 for removal of Am. The results indicated that the presence of alcohol in the scintillator solution helps in increasing the distribution ratio. Experiments were carried out with column containing either MPBPA resin alone or with additional resin bed of Amberlite IR-120 using active organic liquid scintillator waste (with and without dilution with alcohol). Studies were also carried out on alcoholic waste generated in the laboratory during the washing of the used liquid scintillator vials. The alcohol after removal of activity either could be reused or could be disposed off directly as a ‘potentially’ active waste.

Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. This investigation describes the interaction of plutonium in mixed oxidation states (Pu(VI) and Pu(IV)-polymers) with cells of the sulfate-reducing bacterial (SRB) strain Desulfovibrio äspöensis DSM 10631 T , which frequently occurs in the deep granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden. In this study, accumulation experiments were performed in order to obtain information about the amount of Pu bound by the bacteria in dependence on the contact time and the initial plutonium concentration. We used solvent extractions, UV-Vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy to determine the speciation of Pu oxidation states. Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to study the coordination of the Pu bound by the bacteria. In the first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. Solvent extractions showed that 97% of the initially present Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves from the cell envelope back to the aqueous solution due to the weak complexing properties of this plutonium oxidation state. Indications were found for a penetration of Pu species inside the bacterial cells.

We studied the U(VI) sorption onto kaolinite in batch experiments in the absence and presence of humic acid (HA) under different experimental conditions: [U] 0 = 1 × 10 -6 M or 1 × 10 -5 M, [HA] 0 =10 or 50 mg/L, I =0.1 M or 0.01 M NaClO 4 , pH=3–10, CO 2 or N 2 atmosphere. The study showed that the U(VI) sorption onto kaolinite is influenced by pH, CO 2 and HA presence. In the absence of CO 2 , the U(VI) uptake increases with increasing pH value up to pH 6. Above pH 6 it remains unchanged. Because of the formation of negatively charged uranyl carbonate complexes, the decrease in the U(VI) sorption onto the negative surface of kaolinite was observed above pH 8 in the presence of CO 2 . In presence of HA, the adsorption of U(VI) closely follows the adsorption of HA. In the acidic pH range the U(VI) uptake is enhanced compared to the system without HA due to the formation of additional binding sites for U(VI) coming from HA adsorbed onto kaolinite. The formation of aqueous uranyl-humate complexes reduces the U(VI) sorption in the near neutral pH range. The enhancement of the U(VI) concentration from 1 × 10 -6 M to 1 × 10 -5 M results in the shift of the sorption pH edge by one pH unit to higher pH values. The ionic strength has only a slight influence on the U(VI) sorption onto kaolinite, whereas the HA sorption shows a dependence on the ionic strength.

The aim of this study is to explain how the kaolinite-based clay minerals adsorb hexavalent uranium (uranyl ion), and to model uranyl adsorption based on inner-sphere surface complexation with the kaolinite edge hydroxyl sites and outer-sphere complexation with the permanent charge sites. The adsorption of UO 2 2+ on kaolinite-based clay was modeled with the aid of FITEQL 3.2 code using the single-site binding model of the Langmuir approach. Potentiometric titrations and adsorption capacity experiments were carried out in solutions containing different concentrations of the inert electrolyte NaClO 4 , however adsorption modeling was deliberately done at low ionic strength (0.01 M electrolyte) for enabling adsorption onto the permanent negatively charged sites of kaolinite. When a ‘two-site’ binding model was adopted, i.e. , ≡S 1 OH sites representing silanol and ≡S 2 OH sites aluminol, a good fit was not obtained, and therefore the involvement of merely aluminol sites in surface complexation was assumed along with the ion exchange-held X 2 2- –UO 2 2+ species by the NaX permanent charge sites. The uranyl cation was assumed to bind to the clay surface as the sole (unhydrolyzed) UO 2 2+ ion and form monodentate surface complexes. The modeling system comprised of surface complexation and ion exchange was resolved with respect to species distributions and relevant stability constants. Electrostatic effects were accounted for using a diffuse layer model (DLM) requiring the minimum number of adjustable parameters. Metal adsorption onto clay showed a steady increase with increasing pH up to pH 5.5, i.e. , the edge pH for bulk precipitation at the studied concentration range.

The complex formation of uranium(VI) with L -threonine and O-phospho- L -threonine was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). An increase in fluorescence emission intensity and a corresponding red shift of the bands in the spectra compared to the free uranyl cation indicate a complex formation between UO 2 2+ and the non- and phosphorylated amino acid L -threonine. The complex formation constants for a 1:1 and 1:2 complex in the case of L -threonine were determined to be log β 111 =10.33 ± 0.26 at ionic strength I =0.1 M, log β 111 =10.25 ± 0.25 and log β 122 =19.94 ± 0.24 at ionic strength I =0.5 M. The calculated constants of the different 1:1 uranyl complexes with O-phospho- L -threonine are log β 131 =0.28 ± 0.11, log β 121 =18.94 ± 0.29 and log β 111 =15.02 ± 0.23 at I =0.1 M.

Differential thermal and thermogravimetric analyses of actinide metal o -hydroxy N,N ′ -dimethylbenzylamine complexes of the formulae, [LMO 2 X 2 ], [LMO 2 SO 4 ] and [LTh(NO 3 ) 4 ], where M = U, L = o -C 6 H 4 OHCH 2 N(CH 3 ) 2 and X = Cl 2 , NO 3 - have been carried out to explore their degradation patterns. The evolved products were identified on the basis of loss in weight on TG coupled with DTA curves. The thermal decomposition of these complexes occurred with the loss of inorganic and organic fragments and exhibited almost similar mode of degradation with minor differences. The composition of the intermediates formed during degradation was confirmed by microanalysis and IR spectroscopy. The residues, after heating above 545°C, corresponded to metal oxides. Degradation mechanisms of these complexes have also been proposed.

Complexing behaviour of three dihydroxybenzenes (DHB) namely, hydroquinone, resorcinol and catechol with Th(IV) along with their protonation constants were studied in 1 M NaClO 4 medium at 23 ± 0.5 °C, using pH titration technique. Both protonation and metal-ligand equilibrium constants of dihydroxybenzenes were computed using advance software suite of program HYPERQUAD. Logarithmic values of overall protonation constants (log β 1H and log β 2H ) were found to be 11.47 ± 0.05 and 21.45 ± 0.06, for hydroquinone, 11.76 ± 0.04 and 20.98 ± 0.04 for resorcinol and 12.58 ± 0.03 and 21.87 ± 0.08 for catechol respectively. Complex formation has been investigated in the pH range 2 to 4. The logarithmic values of metal-ligand equilibrium constants obtained in the present work were β 13-1 =48.51 ± 0.67 and β 14-1 =64.86 ± 1.25 for hydroquinone, β 110 =16.98 ± 0.16, β 13-1 =46.46 ± 0.18 and β 14-2 =59.65 ± 0.20 for resorcinol and β 11-1 =14.06 ± 0.10 for catechol. The literature values were reviewed.

Due to interesting tumor seeking properties of bis -thiosemicarbazones, two radio palladium- bis -thiosemicarbazone complexes, i.e. , [ 103 Pd]-pyruvaldehyde- bis ( N 4 -methylthiosemicarbazone) ([ 103 Pd] PTSM) and [ 103 Pd]- di -acetyl- bis ( N 4 -methylthiosemicarbazone) ([ 103 Pd]ATSM) were prepared according to the analogy of radio copper homologs. Palladium-103 ( t 1/2 =16.96 d) was produced via the 103 Rh( p , n ) 103 Pd nuclear reaction with proton energy 18 MeV. The final activity was eluted in form of Pd(NH 3 ) 2 Cl 2 in order to react with bis -thiosemicarbazones to yield [ 103 Pd]-labeled compounds. Chemical purity of the product was confirmed to be below the accepted limits by polarography. [ 103 Pd]-labeled bis -thiosemicarbazones were prepared with a radiochemical yield of more than 80% at room temperature after 60–90 min by vortexing a mixture of thiosemicarbazones and Pd activity in ethanol. The purification of the labeled compounds performed by reverse phase column chromatography using C 18 plus Sep-Pak. Radiochemical purity of more than 99% specific activity of about 12500–13000 Ci/mol was obtained. The stability of the complexes was checked in final product and presence of human serum at 37 °C up to 48 h. The partition co-efficients of the final complexes were determined. The initial physico-chemical properties of the labeled compounds were compared to those of their copper homologues.

This study deals with the assessment of potential of Broussonetia papyrifera leaves as biomonitors of air pollution. The leaves samples were collected from urban areas, i.e. , road sides with variable traffic load, industrial areas, as well as from a rural area as a reference site. Leaves samples have been analyzed for 34 elements using instrumental neutron activation analysis (INAA) in combination with atomic absorption spectrophotometry (AAS). The reliability of the methods used was established by analyzing reference materials (RMs) under identical experimental conditions and comparing the results obtained with the certified values, which are in quite good agreement with each other. The results obtained from different sites showed promising potential of this species as multi-elements environmental biomonitor due to their ability to reflect the levels of air pollution in the vicinity in which they grow.