Volume 97, Issue 6

Interaction of trivalent lanthanides and Cm(III) with humic acid (HA) (10 mg/L) is studied as a function of metal ion concentration (1×10 -8 to 5×10 -5  mol/L) and pH (2.5 to 7.0) in 0.01 mol/L NaClO 4 . Time resolved laser fluorescence spectroscopy (TRLFS) reveals a slight blue-shift/broadening of the fluorescence peak position for the Cm(III)-HA complex combined with an enhanced contribution of a short-lived fluorescence component with increasing metal ion loading and decreasing pH. Fluorescence decay for Cm(III)-HA is non-monoexponential under all investigated conditions and lifetimes can be described by assuming a short lived (τ=61 μs) and a longer lived contribution (τ=142 μs). These findings are explained by the existence of a certain heterogeneity in binding sites inducing slightly variable ligand-field splitting in the Cm(III)-HA complex. Batch experiments with a Eu(III)-HA solution contacted with a chelating resin reveal a decrease of the solid/liquid distribution coefficient by decreasing the occupancy of HA ligand sites from 4% to 0.2%. This observation indicates that complexation constants for the Eu(III)-HA complex vary with metal loading. Differences in related constants are, however, smaller than one order of magnitude. Variations in fluorescence lifetimes are interpreted as a consequence of increasing HA agglomeration at increasing metal loading and decreasing pH, thus leading to an enhanced local density of chromophoric groups close to the Cm(III) ion favouring non-radiative energy transition. HA agglomeration at low pH and increasing metal ion loading is well known from previous studies using flow-field flow fractionation (FFF) coupled to ICP-mass spectrometry and UV-Vis spectrophotometry. Our experimental results demonstrate the dynamic properties of metal-HA complexes depending on chemical conditions.

Free-liquid electrophoresis was used for the study of thorium complexation with Aldrich humic acid (HA) in aqueous solutions of 0.01 M (NaClO 4 +HClO 4 or NaOH) with dependence on pH and concentration of thorium (≤10 -9 −10 -5  M, labelled with 234 Th) and HA (0.1−10 mg/L). The abundances and the mean electrophoretic mobilities of thorium humate complexes were calculated from the electrophoretic mobilities of thorium measured. It has been found that negatively charged humate complexes dominate in the solutions of pH 2–11 containing 1−10 mg/L HA and up to 0.001 M HCO 3 - . Experimental evidence was given of the formation of Th(OH) 4 HA y - complex at pH 8–11 and its stability constant was determined. New conclusions about spontaneous association of HA molecules at pH 2–6 and about binding of thorium by non-dissociated carboxyl groups of HA were drawn.

Eu(III) sorption on TiO 2 (anatase) was investigated as functions of pH, ionic strength and Eu(III) concentration by using a batch experimental method. It was found that Eu(III) sorption on anatase is strongly pH-dependent, but insensitive to ionic strength. A constant capacitance model with three inner-sphere surface complexes, ≡SOEu 2+ , ≡SOEuOH + and ≡SOEu(OH) 3 - , was used to interpret Eu(III) sorption on anatase in the absence and presence of carbonate ( p CO 2 =10 -3.58  atm).

Three structural isomers of diamides of dipicolinic acid ( N , N ′-diethyl- N , N ′-ditolyl-dipicolinamide, EtTDPA) with varying position of the methyl group on the tolyl ring have been synthesized and investigated on extractability toward U(VI). The polar diluent FS-13 was used, and distribution ratios of U(VI) were studied as a function of nitric acid, ligand, and lithium nitrate concentrations. Extractability of uranium was shown to increase with increased concentration of nitrate and ligands. Infrared spectra of organic extraction phases indicate that nitric acid is coextracted as part of the neutral metal-ligand complex with U(VI) and EtTDPA through hydrogen bonding with the carbonyl group in the amide moiety.

The liquid-liquid extraction behavior of short-lived molybdenum and tungsten isotopes from HCl and HNO 3 as well as HF/HNO 3 acid media was studied using the α-benzoinoxime/chloroform system. The goal of the present experiments was to find an extraction system with a high selectivity for the group 6 elements in the periodic table which is suitable for the study the solution chemistry of seaborgium ( Z =106). It was found that Mo and W are both effectively extracted using α-benzoinoxime as an extractant and the maximum extraction yield is 100% and 94% for Mo and W, respectively. Ions of MO 2 2+ (M=Mo, W) exist in HCl between the concentration range of 0.1−3 M and can be extracted quantitatively into the organic phase. The decrease of extraction yields at lower or higher acid concentration is due to the formation of anionic species MO 4 2- or MO 2 Cl 3 - . The extraction behavior of Mo and W in HNO 3 solution is similar to that in HCl solution. In HNO 3 /HF mixed acid solutions, due to the formation of MO 2 F 3 - a decrease of extraction yield at higher HF concentration, similar to the case of HCl is observed. The extraction equilibrium is reached within 10−30 s, which means the extraction kinetics of α-benzoinoxime/chloroform extraction system is fast enough for the study of the isotope 265 Sg. The extraction behavior of molybdenum and tungsten shows a distinct difference in the range of 0.05 to 0.2 M HF with 1 M HNO 3 . This shows that differences in the complexation with fluoride ion exist in Mo and W. This study focuses on the investigation of the tendency of group 6 element for complexation with fluoride ion.

A method is proposed to produce the short-lived radionuclide 95g Tc via formation of the parent 95 Ru. To produce 95 Ru, the bombardment of molybdenum target of natural isotopic composition with α-particles and the irradiation of ruthenium of natural isotopic composition with bremsstrahlung photons were used. It is shown that the isotopic purity of 95g Tc produced by suggested methodology is significantly higher compared with other techniques. Attention was also paid to the production of side products such as 95m Tc, 96 Tc, and 97,103 Ru, in order to utilize optimally the energy of the alpha particle beam.

Rhenium-188 is a well recognized therapeutic radionuclide and its use in a variety of applications has been reported. The current methods of obtaining “no-carrier added” 188 Re from conventional alumina based generators require 188 W of very high specific activity for obtaining reasonable quantities of 188 Re in an adequately concentrated form. We have developed a simple electrochemical separation technique adaptable for using low specific activity 188 W, for the separation of 188 Re from 188 W, and obtain 188 Re amenable for radiolabeling biomolecules. The overall decay corrected yield of 188 Re was >70%. The recovered 188 Re had high radiochemical (>97%) and radionuclidic purity (>99.99%). The suitability of the 188 Re for radiolabeling was demonstrated by its use for the complexation of DMSA and HEDP with labeling yields >98%. Repeated separation of 188 Re from a stock solution of 188 W could be demonstrated for a period of 70 d. The preliminary results suggest that the process can be scaled up to higher activity levels and suggest that this strategy can be further explored for the development of electrolytic type 188 W/ 188 Re generator suitable for clinical applications.

The recently developed ligand MF2-BTBP dissolved in cyclohexanone is a promising solvent for the group separation of trivalent actinides(III) from the lanthanides(III). Its high stability against nitric acid has been demonstrated recently. Since the solvent is also exposed to a continuously high radiation level in the counter current process, the radiolytic stability of the solvent was examined in this study. Irradiation experiments were carried out up to an absorbed dose of 100 kGy and the effect of the dose rate was investigated. The extraction behaviour for An(III)/Ln(III) separation was studied after radiolysis for evaluation. It was found that during high dose rate irradiation the extraction efficiency for both Am(III) and Eu(III) decreased significantly with increasing absorbed dose, whereas during the low dose rate irradiation the extraction efficiencies remained more or less at the same level.

Elemental analysis of some medicinal plants used in the Indian Ayurvedic system was performed by employing instrumental neutron activation analysis (INAA) and atomic absorption spectroscopy (AAS) techniques. The samples were irradiated with thermal neutrons in a nuclear reactor and the induced activity was counted by gamma ray spectrometry using an efficiency calibrated high resolution high purity germanium (HPGe) detector. Most of the medicinal plants were found to be rich in one or more of the elements under study. The variation in elemental concentration in same medicinal plants samples collected in summer, winter and rainy seasons was studied and the biological effects of these elements on human beings are discussed.

Three highly sensitive analytical methods: epithermal neutron activation analysis (ENAA), radiometric assay and UV/Vis spectroscopy were used to investigate the elemental composition of both halite and mineral fractions (sediments) of salt collected from the Slanic-Prahova salt mine, near the location of Low Background Radiation Laboratory. For halite with all three methods and within experimental uncertainties, it was not possible to observe the presence of any natural radioactive elements. For the mineral fraction both radiometric and ENAA showed the presence of 40 K, 232 Th and 238 U in concentrations comparable to the upper continental core (UCC). The same was true for the distribution in the mineral fraction of 7 other major (Na, Al, Cl, K, Ca, Ti and Fe) and 29 trace elements (Sc, Cr, V, Mn, Ni, Co, Zn, Cu, As, Br, Rb, Sr, Zr, Mo, Sn, Sb, Cs, Ba, La, Ce, Ne, Eu, Sm, Tb, Hf, Ta, W, Th, U) as determined by epithermal neutron activation analysis (ENAA), which demonstrates a continental origin of the sediments in the existing salt deposit.