Instrumental activation analysis (IAA) in a sequential analytical procedure has been developed and applied to the determination of 14 common bulk major and minor elements in a wide variety of rock types, ranging from dunites to granites, and in a variety of stone meteorite specimens. This sequential nondestructive technique consists of 14 MeV neutron (~ 1010 nvt) activation for Si(28A1) and O (16N); thermal-neutron (~ 2 × 109) nvt) for Al (28A1); thermal-neutron (~ 1013 nvt) for Na (24Na) and Mn (56Mn); thermal-neutron (~ 1014 nvt) for K (42K); 23 MeV bremsstrahlung (~ 2 × 106 roentgens) for Mg (24Na); 28 MeV bremsstrahlung (~ 8 × 107 roentgens) for Ca (47Ca), Ti (47Sc) and Ni (57Ni); thermal-neutron (~ 2 × 1015 nvt) for Cr (51Cr), Fe (59Fe), Co (60Co) and Ba (181Ba); all radionuclides were counted by either NaI(Tl) or Ge(Li) detectors. Sc (46Sc) and Cu (64Cu) abundances are obtained in the thermal-neutron activations for the element groups of Cr and K. Elemental abundances agreed within + 1-5% of literature values; in some cases, IAA values were considered superior to classical analyses. After IAA for the 14 bulk elements, the rock specimens may be subjected to further chemical and physical measurements.
To study the complex formation of group 5 elements (Nb, Ta, Ha, and pseudoanalog Pa) in aqueous HCI solutions of medium and high concentrations the electronic structures of anionic complexes of these elements [MCl_6]^-, [MOCl_4]^-, [M(OH)-2 Cl_4]^-, and [MOCl_5]^2- have been calculated using the relativistic Dirac-Slater Discrete-Variational Method. The charge density distribution analysis has shown that tantalum occupies a specific position in the group and has the highest tendency to form the pure halide complex, [TaCl_6-. This fact along with a high covalency of this complex explains its good extractability into aliphatic amines. Niobium has equal trends to form pure halide [NbCl_6]^- and oxyhalide [NbOCl_5]^2- species at medium and high acid concentrations. Protactinium has a slight preference for the [PaOCl_5]^2- form or for the pure halide complexes with coordination number higher than 6 under these conditions. Element 105 at high HCl concentrations will have a preference to form oxyhalide anionic complex [HaOCl_5]^2- rather than [HaCl_6]^-. For the same sort of anionic oxychloride complexes an estimate has been done of their partition between the organic and aqueous phases in the extraction by aliphatic amines, which shows the following succession of the partition coefficients: P_Nb < P_Ha < P_Pa.
Multiconfiguration relativistic Dirac-Fock (MCDF) values were calculated for the first five ionization potentials of element 105 (unnilpentium) and of the other group 5b elements (V, Nb, and Ta). Some of these ionization potentials in electron volts (eV) with uncertainties are: 105(0), 7.4±0.4; 105(1 +), 16.3 ±0.2; 105(2 +), 24.3 ± 0.2; 105(3 + ), 34.9 ± 0.5; and 105(4 + ), 44.9 ± 0.1. Ionization potentials for Ta(1+), Ta(2 +), and Ta(3 + ) were also calculated. Accurate experimental values for these ionization potentials are not available. Ionic radii are presented for the 2+, 3+, 4 +, and 5+ ions of element 105 and for the + 2 ions of vanadium and niobium. These radii for vanadium and niobium are not available elsewhere. The ionization potentials and ionic radii obtained are used to determine some standard electrode potentials for element 105. Born-Haber cycles and a form of the Born equation for the Gibbs free energy of hydration of ions were used to calculate the standard electrode potentials.
Element 106, isotope mass number presumably 263, detected by its spontaneous fission, has been isolated from the products of the bombardment of 249Cf with 18O by the thermochromatography of oxochlorides. Specifically, it was separated from elements 105, 104 and heavy actinoids. Dioxodichloride seems to be responsible for the observed behaviour of element 106. Some 40 atoms of the element have been registered.
Chemical separations of element 106 (seaborgium, Sg) were performed in aqueous solutions. The isotopes 265Sg and 266Sg, produced in the 248Cm+22Ne reaction, were continuously transported to the automated liquid chromatography system ARCA. In 0.1 M HNO3/5×10−4 M HF, Sg was found to be eluted from cation-exchange columns together with the hexavalent Mo- and W-ions, while hexavalent U-ions were strongly retained on the column. Seaborgium was detected by measuring correlated α-decays of the daughter isotopes. For the isotope 266Sg, we have evidence for a spontaneous fission branch. The chemical results show that the most stable oxidation state of Sg in aqueous solution is +6, and that like its homologs Mo and W, Sg forms neutral or anionic oxo- or oxohalide-compounds. Sg exhibits properties very characteristic of group 6 elements, and does not show U-like properties. A second, very recent experiment, performed with pure 0.1 M HNO3, gave evidence that the F−-anions contributed significantly to the complex formation in the first experiment.
The beta(+)/EC ratio in the decay of I-120g (T-1/2 = 1.35 h), i.e. the beta(+) emission intensity, was measured for the first time using a high purity I-120g source, which was produced by irradiation of 99.0% enriched Te-120 with 15 MeV protons, followed by a chemical separation of radioiodine. Both gamma-ray and X-ray spectroscopy were applied. In the former case a comparison of the intensity of the annihilation radiation with that of the 1523 keV gamma-ray of I-120g was done and in the latter case with that of the K-alpha or K-beta X-ray of the daughter tellurium. Corrections for very small contributions of I-121 and I-120m impurities were evaluated. The literature values for the Ibeta+ of I-120g range between 39 and 81%. Our measurements lead to a value of 56 +/- 3 %.
For the assessment of the long-term safety of a geological disposal of high- and intermediate level radioactive waste and/or spent fuel in the Boom Clay, a better understanding of the migration behaviour of Natural Organic Matter (NOM) is needed because it can act as a carriermolecule for radionuclides. Therefore, a large-scale in-situ migration experiment with 14C-labelled NOM was performed to study the NOM migration behaviour on a large scale (m), on the long-term (> 10 years) and in directions parallel and perpendicular to the bedding plane (transport anisotropy). The numerical modelling tool HYDRUS2D/3D was used to interpret the results. The model was built stepwise, testing the influence of advection, colloid attachment/detachment and anisotropy. The upscaling of previously determined parameters from small scale lab tests was also tested. A classic diffusion-advection description, using parameter values in the range of those obtained in the lab tests, provided already reasonable results. Inclusion of a colloid filtration term in the model significantly improved the simulation. Finally, the model was succesfully tested against a second dataset and the anisotropy of the Boom clay was brought into account.
The available experimental data on the most common route for the production of F-18, viz. O-18(P, n)F-18 reaction, obtained both via neutron spectral studies and activation measurements, were critically reviewed. In some energy regions the cross section database was found to be rather weak or discrepant. In order to fill the gaps and to clear some of the discrepancies, the excitation function was remeasured from threshold up to 30 MeV using different solid and gas targets containing highly enriched O-18. For this purpose a van de Graaff machine (E-p < 4 MeV) and several cyclotrons (E-p = 4-30 MeV) were utilized. The new experimental data help to prepare a recommended data set. At E-p = 14 MeV the integral yield of 18F calculated from the new excitation curve is slightly higher than that from the hitherto accepted data set; at E-p > 14 MeV the yields reported here are new.
The production cross sections of tritium from oxygen have been measured in p-Be and p-Li neutron fields installed at the sectorfocusing (SF) cyclotron of the Institute for Nuclear Study (INS), University of Tokyo. Irradiations were performed with the semi-monoenergetic neutrons produced from the 9Be(P,P)9B reaction at proton energies from 20 up to 40 MeV in 2.5-MeV steps, and those from 7Li(p,n)7Be in 5-MeV steps with proton intensities of 2-5 μA, which yields neutron flux densities from 107 to 108 n/cm2/sec at the position of sample irradiation. The neutron energy spectra were determined by an NE-213 scintillation counter. The tritium produced in the water used as the oxygen target was extracted by a distillation method, and measured by a liquid scintillation counter. The excitation functions for the 16O(n,t)14N reaction, measured by the p-Be and p-Li neutrons, agreed well with each other within the experimental uncertainties. The obtained results have been compared with the general trend in the (n,t) cross sections as a function of the atomic number of the target appearing in the literature.
In connection with the production of 46.2min
51Mn via the 50Cr(d, n)-process, several separation techniques
such as ion exchange chromatography, solid phase extraction,
liquid–liquid extraction and co-precipitation have been
investigated; the aim was to separate no-carrier-added radiomanganese
from the bulk target chromium. Among the
separation systems ∗MnII/CrIII , ∗MnII/CrVI and ∗MnIV/CrVI ,
the latter applying the co-precipitation of ∗MnIV with FeIII
hydroxide was found to be the optimum; the removal of
chromium was rapid and quantitative (remaining content
< 0.05%) and the separation efficiency was high (99.3%
radiochemical yield of ∗Mn). For production purposes, a sandwiched
pellet of the chemical composition Al4 ·50CrCl3 was
developed as a new target. This allowed a quick dissolution
after irradiation, thus enabling a fast separation of 51Mn
and its production on a MBq scale. A 1 h irradiation at
3 μA (wobbled beam) over an effective deuteron energy range
of Ed = 12.8→7.9MeV yielded 107 MBq 51Mn. Simultaneously
formed nuclides of other elements, such as 38Cl, 24Na,
48V and 51Cr were quantitatively separated using the proposed
procedure. Only the shorter-lived radioisotope 52mMn,
formed via the 52Cr(d, 2n)52mMn reaction, was present at
a low level of 2%, if the enrichment of 50Cr was 95%
(with ∼ 5% 52Cr).
The excitation function of the Zn-68(p, 2 p)Cu-67 reaction was measured radiochemically up to a proton energy of 71MeV to obtain accurate data for production of the therapy related beta(-)-emitting radioisotope Cu-67 (T-1/2 = 61.9 h). Investigations were also made on the (p, 2n) and (p, 3n) reactions on Zn-68. The experimental cross sections of the Zn-68(p, 2 p)Cu-67, Zn-68(p, 2n)Ga-67 and Zn-68(p, 3n)Ga-66 reactions were compared with published data and with theoretical predictions based on the hybrid-precompound model ALICE-IPPE. Thick target yields Of Cu-67, Ga-67 (T-1/2 = 78.3 h) and Ga-66 (T-1/2 = 9.4 h) were calculated. Production Of Cu-67 is feasible only at proton energies above 50 MeV. For the target thickness E-P = 70 --> 50 MeV, the yield of Cu-67 amounts to 16.9 MBq/muA(.)h.
The present work describes two radiosynthetic pathways to prepare homocysteine[ ⁷⁵ Se]selenolactone 1 starting from n.c.a. [ ⁷⁵ Se]selenite 2 . It was achieved either by alkylation reaction of n.c.a. methyl[ ⁷⁵ Se]selenide 4 or by hydrolysis of alkylated 1,3-dicyclohexyl[ ⁷⁵ Se]selenourea 11 .
N.c.a. methyl[ ⁷⁵ Se]selenide 4 is available using sulfur as non-isotopic carrier. However, the radiochemical yield of the substitution of 2-tert.-butoxycarbonylamino-4-bromobutyric acid ethylester 5 with n.c.a. methyl-[ ⁷⁵ Se]selenide is only in the range of 15-20%. Birch reduction of protected n.c.a. [ ⁷⁵ Se]selenomethionine 6 formed leads to a RCY of 5-10% homocysteine[ ⁷⁵ Se]selenolactone 1 .
Alternatively, the synthesis of homocysteine[ ⁷⁵ Se]selenolactone 1 is possible by hydrolysis of the corresponding [ ⁷⁵ Se]selenouronium salt 11 available by addition of 2-tert.-butoxycarbonylamino-4-bromobutyric acid ethylester 5 to 1,3-dicyclohexyl[ ⁷⁵ Se]selenourea 10 . A method was developed for the synthesis of 1,3-dicyclohexyl[ ⁷⁵ Se]selenourea 10 by addition of c.a. [ ⁷⁵ Se]SeH 2 to 1,3-dicyclohexylcarbodiimide, which leads to 20-30% RCY of c.a. homocysteine[ ⁷⁵ Se]selenolactone 1 .
The radioisotope Nb-90 decays with a positron branching of 53% and a relatively low beta(+)-energy of E-mean = 0.66 MeV and E-max = 1.5 MeV. Its half-life of 14.6 h makes it especially promising for quantitative investigation of biological processes with slow distribution kinetics using positron emission tomography. To optimise its production, the excitation functions of Zr-90(p, xn)-processes were studied over the proton energy range of 7.5 to 19 MeV via the stacked-foil technique using both Zr-nat and 99.22% enriched (ZrO2)-Zr-90 as targets. Thick target yields of Nb-90 were calculated from the measured excitation functions and were verified experimentally. The optimum energy range for the production of Nb-90 via the Zr-90(p, n)-process was found to be E-p = 17 --> 7 MeV, with a yield of 600 MBq Nb-90/muA h. The yield and radionuclidic purity of Nb-90 over the energy range of E-p = 17.6 --> 8.1 MeV were determined experimentally using Zr-nat. At 4 h after EOB the yield of Nb-90 was found to be 290 MBq/muA h and its radionuclidic purity greater than or equal to 95%.
Accurate partial gamma-ray production cross sections were determined for the prompt and radioactive product decay gamma rays following cold neutron capture in 99 Tc. They can be used for non-destructive assay of tech- netium by prompt gamma activation analysis (PGAA) and neutron activation analysis (NAA), offering orders of mag- nitude higher analytical sensitivities than passive gamma-ray counting. A lower limit of 21.21 ± 0.17 b was also deduced for the thermal-neutron-capture cross section.
Long-lived radionuclides produced by cosmic rays in extraterrestrial matter not only preserve information about the irradiated objects themselves, e.g. meteorites, Moon or Mars, but they also give hints about the spectral distribution and constancy of the cosmic ray flux. Due to the scarcity of the investigated material and the low concentrations of those so-called cosmogenic nuclides, a highly sensitive analytical technique is needed. Accelerator mass spectrometry (AMS) meets this requirement, but radiochemical separation of samples prior to the AMS measurement is necessary. For that purpose we improved separation procedures with respect to the special demands on measurements of heavier nuclides like 53Mn, 59Ni, and 60Fe via AMS, especially focussing on high decontamination of interfering isobars. ̈ by Oldenbourg Wissenschaftsverlag, München.
The complex formation constants of tetravalent plutonium ion with malonic and succinic acids in aqueous solution were determined by the solvent-extraction method. Also, by taking the known values of the solubility products, the hydrolysis constants and the formation constants, the experimental solubility data of plutonium in the presence of carboxylates were analyzed.
Systematic trends of mononuclear hydrolysis constants of actinide ions were studied with the use of a simple hard sphere model. In the analysis of the literature data of hydrolysis constants, not the formal but the effective charges of actinide ions were considered since some additional interactions were expected for actinide ions as well as ordinary electrostatic ones. Systematic trends in the hydrolysis constants were well explained by the present model. The evaluated effective charges were found to be correlated-with the radial distribution of 5f orbitals, and an empirical equation was given for the correlation between the effective charges and radial expectation values. A useful method was given in the present analysis to check the experimental data and to predict the unknown data from a systematic point of view.
The complexation of redox sensitive elements by humic acid (HA), described through the charge neutralisation model (CNM), has been reviewed in order to have a comprehensive scope. The data acquired in HUMICS program on thorium(IV), and data available in the literature, were reinterpreted according to the CNM, and adapted to uranium(IV), neptunium(IV) and plutonium(IV) through analogy in order to draw a boundary prediction. Otherwise, available data obtained in the framework of the CNM were used, or adapted if necessary, for other redox states when the analogy is justified,
The obtained speciation diagrams indicate that, when (HA)=100 mg/L, redox sensitive actinides should be reduced to their +IV state when
The distribution coefficients of Am. Ce, and Eu between the salt and metal phases were measured at 1073 K in a reductive extraction system of equimolar NaCl-KCl melt and liquid Ga. By changing the solute concentrations, it was observed that the distribution coefficients were dependent on the oxide ion concentration in the system, possibly due to the formation of such compounds as AmO(+). In addition, the mass balance of Am was possibly affected by the formation and precipitation of its oxychlorides and/or oxides in some runs. Taking these observations into consideration, the separation factor between Am and Cc was found to be around 30 in the present system.
The direct electrophilic no-carrier-added (n.c.a.) aromatic radioiodination was examined using various metal salts in trifluoroacetic acid (TFA) as in situ oxidation agents. Two different types of metal salts were used comprising TFA-soluble (Pb(CH3CO2)(4), Mn(CH3CO2)(3), KMnO4, Tl(CF3CO2)(3), AgCF3SO3) and TFA-insoluble (Ce(CF3SO3)(4), RuCl3, FeBr3, K2Cr2O7) salts. Optimization of both labelling systems has been performed using Pb(CH3CO2)(4), Ce(CF3SO3)(4) and benzene as a model substrate. At room temperature, the one-pot synthesis was completed within 15 min, resulting in a radiochemical yield of 82% and 64% using Pb(CH3CO2)(4) and Ce(CF3SO3)(4), respectively. Radioiodination of weakly activated monosubstituted benzene derivatives led to high radiochemical yields of about 80% and 60% of the corresponding ortho- and para-radioiodo-isomers using both salts. Weakly deactivated chlorobenzene could only be radioiodinated with Ce(CF3SO3)(4) as oxidant, forming exclusively the para-product with a radiochemical yield of about 35 %. Using the optimized reaction parameters for the other TFA-soluble and -insoluble metal salts with benzene and toluene good radiochemical yields were obtained in all cases except for the manganese and silver salts. Apparently their oxidation power was not strong enough for the radioiodination of the non-activated benzenes. In situ formed trifluoroacetyl [I-131]hypoiodite is discussed with regard to the reaction mechanism.
Majolica pottery was the most characteristic tableware produced in Spain during the Medieval and Renaissance periods. A study of the three main production centers in the historical region of Aragon during Middle Ages and Renaissance was conducted on a set of 71 samples. The samples were analyzed by instrumental neutron activation analysis (INAA), and the resulting data were interpreted using an array of multivariate statistical procedures. Our results show a clear discrimination among different production centers allowing a reliable provenance attribution of ceramic sherds from the Aragonese workshops.
The solid–liquid distribution of europium (Eu) between an adsorptive surface and a solution phase containing a competitive colloid is the result of a delicate balance between several individual chemical reactions. In this study, adsorption isotherms of Eu in presence of dissolved Boom Clay natural organic matter were experimentally determined under conditions relevant for a geological repository (trace Eu concentrations, anoxic conditions, ∼0.014 mol l ⁻¹ NaHCO 3 background electrolyte). It was found that both the concentration and size distribution (or operational cut-off used to discriminate between “mobile” and “immobile” colloids) of natural organic matter has a strong influence on the observed solid–liquid distribution.
The experimental data were subsequently modelled using a component additive approach with two well-established sorption/interaction models: the 2 SPNE SC/CE model for describing Eu adsorption on illite, and Humic Ion-Binding Model VI for describing Eu complexation to natural organic matter. Model parameters were gathered from dedicated measurements in batch systems containing only Eu and the interacting phase under study, under similar conditions as in the ternary isotherm experiments. Mutual interactions between illite and natural organic matter were studied and quantified. Under the experimental conditions of this study, it was found that these interactions were only of minor importance.
The two models were subsequently combined to blind predict the Eu solid–liquid distribution in the ternary batch experiments. Within an error margin of 0.5logߙ K d units, the additivity approach succeeded well in predicting Eu uptake in all experimental systems studied. A sensitivity analysis was performed to select the most important model parameters influencing the Eu uptake, and the robustness of the model. This study has shown that the component additivity approach for describing and predicting uptake of trivalent lanthanides/actinides under Boom Clay conditions, is promising, and may help in unraveling the complex behaviour of these radionuclides witnessed in migration experiments.
The chemistry of the actinides has long been an area of great interest to many researchers, due to the unusual nature of the f-orbital electrons. Electron spectroscopies provide a useful means to study the electronic structure of the 5 f states, and how they affect the interactions of the actinide elements with various molecules. In this Study the interaction of ammonia with a polycrystalline thorium surface at two different temperatures has been investigated using X-ray and ultraviolet photoelectron spectroscopic techniques. Exposure to ammonia at ambient temperature results in the formation of both nitride (Th-N) and NH(x) species, characterised by N is photoemission peaks at 396.5 and 398.8 eV binding energy respectively, on the thorium surface. Exposure to ammonia at 100 K gives rise to an additional signal at 401.2 eV corresponding to physisorbed ammonia. Additional UPS results provided corroborating evidence for the effect of the surface temperature on the reaction with ammonia.
An electrorefining process in molten chloride salts using solid aluminium cathodes is being developed at ITU to recover actinides (An) from the spent nuclear fuel. The maximum possible loading of aluminium electrodes with actinides was investigated during the electrorefining of UPuZr alloy in a LiCl-KCl eutectic at 450°C. Two different electrolytic techniques were applied during the experiment and almost 6000 C has been passed, corresponding to 3.7 g of deposited actinides. A very high capacity of aluminium to retain actinides has been proven as the average Al:An mass ratio was 1:1.58 for galvanostatic and 1:2.25 for potentiostatic mode. The obtained deposits were characterized by XRD and SEM-EDX analysis and alloys composed of (U,Pu)Al3 were detected. The influence of zirconium co-oxidation during the process was also investigated and the presence of dissolved Zr ions in the melt yielded a significant deterioration of the quality of the deposit.
The solubility of ThO 2 · x H 2 O(am) is studied at I =0.1−4.0 M (NaHCO 3 -Na 2 CO 3 -NaCl) and 22 °C. Several sets of closed system experiments are performed at total carbonate concentrations of C tot =[HCO 3 ⁻ ]+[CO 3 ²⁻ ]=0.02 and 0.1 M in the range pH c = 8−11. In our recent study at I =0.5 M, the simultaneous evaluation of solubility data at widely varied pH c and carbonate concentrations has shown that Th(OH)(CO 3 ) 4 ⁵⁻ , Th(OH) 2 (CO 3 ) 2 ²⁻ and Th(OH) 4 (CO 3 ) ²⁻ are the most important ternary complexes. The present results at I =0.1−4.0 M are used to describe the ionic strength dependence of the equilibrium constants log K s, 1 yz (for the reactions Th(OH) 4 (am)+ z CO 3 ²⁻ ↔Th(OH) y (CO 3 ) z 4- y -2 z +(4- y )OH ⁻ ) with the SIT. EXAFS measurements in 0.1 and 1.0 M carbonate solutions support the calculated speciation. They show clearly different spectra for the predominant species Th(OH)(CO 3 ) 4 ⁵⁻ and Th(CO 3 ) 5 ⁶⁻ , respectively.
The standard of a primary specialized journal depends to a large extent on the quality of the peer-review process. During the last four years the following persons reviewed one or more manuscripts submitted to Radiochimica Acta, and gave advice to improve the presentations.
The solubility-limiting solid phases in the ternary aqueous systems of Zr(IV)/OH/oxalate, Zr(IV)/OH/malonate, Th(IV)/OH/oxalate and Th(W)/OH/malonate were characterized by elemental analysis, X-ray diffraction, thermogravimetric analysis and differential thermal analysis. The ternary solid phase of M(IV)/OH/carboxylate was observed to form, even under acidic conditions, depending on the pH and the concentration of carboxylate ligand. In the presence of a large excess of carboxylic acid, however; the binary M(IV)-carboxylate solid phase formed.
The pion capture process in gas mixtures containing hydrogen was studied by measuring pionic X rays and π° decays. A little difference in pion transfer process was found between the H2 + D2 and H2O + D2O systems. Pressure-dependence of the transfer rates was also revealed in the CH4 + Ar system by the measurements at several gas pressures. The mechanism of the pion transfer process was discussed based on a comparison between transfer parameters in the gas and liquid phases.
The electronic K X-ray energies of pionic atoms were precisely measured on elements ranging from zinc to lead with a low-energy photon detection system. Some differences between pionic and muonic atoms were found in the atomic-number (Z) dependence of the energy shift. In the pionic atoms, the energy shift gradually decreases with an increase in atomic number, which is opposite to the trend for muonic atoms. In the low-Z region investigated elements, the energy shifts of K-beta X-rays were obviously larger than those of K-alpha X-rays.
In model experiments with W, Hf, Th, and U radionuclides, a chemical system was developed for the separation of seaborgium from element 104 and heavy actinides, i.e., cation exchange on Dowex 50X8 from solutions containing 0.1-1.0 M HCl and 0.5-2.0 vol% H2O2. The system should be suitable for fast online experiments if seaborgium exhibits a non-uranium-like behaviour. Adding hydrogen peroxide to mixed HCl/HF solutions suppresses the partial sorption of W and, presumably seaborgium, on the cation exchanger. This way, the elution volume can be minimized. Prospects for anion exchange separations of group 6 from group 4 elements are also briefly discussed.
An analytical method is described for the estimation of uranium concentrations, of 235U/ 238U and 236U/ 238U isotope ratios and burn-up of irradiated reactor uranium in contaminated soil samples by inductively coupled plasma mass spectrometry. Experimental results obtained at 12 sampling sites situated on northern and western radioactive fallout tails 4 to 53 km distant from Chernobyl nuclear power plant (NPP) are presented. Concentrations of irradiated uranium in the upper 0-10 cm soil layers at the investigated sampling sites varied from 2.1 × 10 -9 g/g to 2.0 × 10 -6 g/g depending mainly on the distance from Chernobyl NPP. A slight variation of the degree of burn-up of spent reactor uranium was revealed by analyzing 235U/ 238U and 236U/ 238U isotope ratios and the average value amounted to 9.4 ± 0.3 MWd/(kg U).
The evaporation behaviour of polonium and its lighter homologues selenium and tellurium dissolved in liquid Pb-Bi-eutecticum (LBE) has been studied at various temperatures in the range from 482 K up to 1330 K under Ar/H2 and Ar/H2O-atmospheres using γ-ray spectroscopy. Polonium release in the temperature range of interest for technical applications is slow. Within short term (1h) experiments measurable amounts of polonium are evaporated only at temperatures above 973 K. Long term experiments reveal that a slow evaporation of polonium occurs at temperatures around 873 K resulting in a fractional polonium loss of the melt around 1% per day. Evaporation rates of selenium and tellurium are smaller than those of polonium. The presence of H2O does not enhance the evaporation within the error limits of our experiments. The thermodynamics and possible reaction pathways involved in polonium release from LBE are discussed.
The influence of natural organic matter (NOM) on the speciation and solubility of europium (Eu) was studied under geochemical conditions representative for the Boom Clay. Different organic matter types were used, and analysis was performed both after 0.45 μm microfiltration and after 30000 MWCO ultrafiltration to distinguish between larger colloids (assumed to be immobile under in situ conditions) and small dissolved species.
Equilibrium was approached from undersaturation starting from synthesised Eu(OH) 3 (s), which, during the experiment, transformed into EuOHCO 3 (s), in agreement with thermodynamic considerations. In the absence of NOM, the Eu solution concentrations after 0.45 μm filtration exceeded the thermodynamic solubility of EuOHCO 3 (s) by several orders of magnitude, indicating the presence of inorganic Eu colloids. In the presence of NOM, the Eu solubility increased with increasing NOM concentration as was expected, but, surprisingly, was dependent on the operational size cut-off: at an identical NOM concentration in the filtrate, the Eu solution concentration after 0.45 μm filtration was consistently higher compared to the Eu concentration after 30000 MWCO filtration. This latter observation necessitates detailed knowledge concerning the pore size cut-off of Boom Clay under in situ conditions in order to use the correct Eu-NOM complexation constant and/or maximum solubility in transport calculations. At higher NOM concentrations (TOC>30 mg/L) the Eu solubility after 0.45 μm filtration was seemingly independent of the NOM concentration.
In contrast, after 30000 MWCO ultrafiltration, the Eu solution increased linearly with increasing DOC, from the expected thermodynamic solubility (∼5×10 ⁻⁷ mol L ⁻¹ ) at 0 mg L ⁻¹ DOC to ∼3×10 ⁻⁵ mol L ⁻¹ at 80 mg L ⁻¹ DOC. All of the data sets were modelled using the Nagra/PSI database  for solubility, hydrolysis and inorganic aqueous complexation reactions, and fitted organic complexation reactions between Eu ³⁺ and NOM functional groups. Both a free ligand approach (with electrostatic correction) and the humic ion-binding model VI , which was for the first time successfully introduced into Phreeqc geochemical code, were tested and provided equally good fits to the data.
The oxidation of Br- by Cl2- is investigated by gamma pulse radiolysis in aqueous solutions of NACl and NaBr. Depending on the ratio of the concentration of Br- to Cl-, the main product being observed is either Cl2-, ClBr- or Br2-. The mixed radical anion ClBr- exhibits a broad absorption band at 350 nm with ε350 = 9300 dm3 mol-1 cm-1. The rate constants of the equilibrium Cl2- + Br- Br- ClBr- + Cl- are determined to be kf = 4 × 109 dm3 mol-1 s-1 and kb = 1.1 × 102 dm3 mol-1 s-1. The formation of the Cl3- (λmax = 220 nm), Cl2Br- (λmax = 230 nm) and ClBr2- (λmax = 245 nm) ions in the radiation-chemical oxidation of Cl- and Br- ions in an aqueous solution was observed by pulse radiolysis, and its mechanisms of appearance and the equilibrium constants were determined.
Extraction equilibrium of lanthanides between tri-butyl phosphate solution and molten calcium nitrate hydrate, which is generally called a hydrate melt, was studied radiochemically, The dependence of the extractions on the water content of the melt was studied at 70 degreesC in the range of R from 3 to 12.6 for Ca(NO3)(2) . RH2O. From the observed distribution ratios, variation of the activity coefficients of lanthanide nitrates in hydrate melts was analyzed as a function of water content. It was found that, in a concentration region of R greater than about 5.7, the increase of the activity coefficients with decreasing R shows a different tendency compared with the more water-abundant region, This is discussed in conjunction with the characteristics of the hydrate melt, as well as with the difference of the ionic size of lanthanide cations.
The U(VI) uptake in degraded cement pastes was undertaken in the laboratories of CEA/L3MR and SUBATECH in order to check the reproducibility of the study. Two well hydrated cement pastes, CEM I (Ordinary Portland Cement, OPC) and CEM V (blast furnace slag (BFS) and fly ash added to OPC) were degraded using similar protocols. Equilibrium solutions and solid materials were characterised for three degradation states for each paste. All samples are free of portlandite and the pH of the equilibrated cement solutions vary in the range 9.8–12.2. Three calcium silicate hydrate phases (C-S-H) were synthesised in order to compare the sorption properties of degraded cement pastes and of hydrate phases in similar pH conditions. In order to avoid precipitation processes, the operational solubility limit was evaluated before batch experiments. These solubility values vary significantly in the pH range [9–13] with a 2.4×10−7 mol/L minimum at pH close to 10.5. In batch sorption experiments, the distribution ratio Rd values are high: 30000–150000 mL/g. The uptake of U(VI) increases when comparing the least and the most degraded cement pastes whereas the initial composition of cement has relatively insensitive effect. Sorption isotherms, expressed as a log [U(VI)solid]/ log [U(VI)solution] plots are linear. A slope of 1 is calculated indicating the predominance of sorption processes. As sorption and desorption values are close, the uptake mechanism seems reversible. The Rd values measured in C-S-H suspensions are in good agreement with Rd values of degraded cement pastes, and C-S-H materials could be one of the cementitious phases which control U(VI) uptake in cement pastes.
The hydrolysis constants of Th(IV) were determined using the solvent extraction method in a NaClO(4) Solution at I = 0.1 and 25 degrees C. A trace amount of thorium below the solubility limit was used in order to avoid the formation of polynuclear species and colloids in the experiment. The values were compared with the literature data. Considering the effect of competitive hydrolysis reactions under weak acid conditions, the complexation constants of Th(IV) with a series of dicarboxylic acids containing different alkyl chain lengths were determined.
The influence of reaction channel on the isomeric cross-section ratio was investigated by analysing the experimental data on the reactions Cr-52(p, n)Mn-52m,Mn-g, Cr-52(He-3, t)Mn-52m.g, Fe-54(d, alpha)Mn-52m.g, Fe-54(n, t)Mn-52m.g and Fe-54(He-3, alpha p)Mn-52m.g over the incident particle energy range extending up to 35MeV. The influence is most pronounced when the channels differ widely, for example (p,n) and (He-3, t) processes, i.e. when the reaction mechanisms are different. The nuclear model calculational code EMPIRE-II described the isomeric cross-section ratio rather well in the case of a simple nucleon emission reaction, but not when complex reaction channels were involved.
Citric acid, a naturally occurring hydroxycarboxylic acid, forms bidentate, tridentate, dinuclear, or polymeric species, depending on the metal. In the presence of iron and uranium a ternary Fe: U: citric acid complex is formed. We determined the molecular structure of the ternary complex in both the aqueous and solid phase. Fourier transform infrared spectroscopy (FTIR) showed the presence of uni- and bi-dentate bonding of the citric acid to the metals, and the involvement of the α -hydroxyl group. Analysis of molecular fragments generated from time-of-flight secondary ion mass spectroscopy (TOF-SIMS) confirmed the bonding of terminal carboxylate groups of citric acid to uranium and iron. Extended X-ray absorption fine structure (EXAFS) analysis revealed the dinuclear nature of the Fe bonding to citrate and mononuclear uranium species with citrate. Coordination of a sodium atom to the iron was also noted. The proposed empirical formula for the complex is [NaFe 2 (μ-O)(μ-citrato)(OH) 2 (H 2 O)(C 6 H 4 O 7 )bis(UO 2 )(C 6 H 5 O 7 )] ⁷⁻ . The structure consists of a dinuclear ferric ion core coordinated through an oxy (μ-O) and a carboxylate (μ-citrato) group of citric acid. The mononuclear uranyl ions are coordinated in bidentate fashion to the central carboxylate groups of citric acid and tridentate coordinated to citric acid.
For the production of radioactive ion beams by means of the ISOL (isotope separation on-line) method in which the nuclei of interest are stopped in a thick target, chemistry plays a crucial role. It serves to separate the nuclear reaction products in atomic or molecular form from the bulk target and to transfer them efficiently to an ion source. This article gives an overview of ISOLDE radiochemical methods where targets (liquid metals, solid metals, carbides and oxides) and ion sources are optimized with respect to efficiency, speed and chemical selectivity. Rather pure beams of non-metals and volatile metals can be obtained with a temperature-controlled transfer line acting as thermo-chromatograph. For less volatile metals the temperature of the target and ion source units needs to be kept as high as possible, but a selective ion source can be used: positive surface ionization for metals with ionization potentials below about 6 eV and the RILIS (resonance ionization laser ion source) technique for most other metals.
The hydrolysis constants and the solubility products of the oxide/hydroxides of Pa(IV) and Pa(V) have been first reviewed and re-evaluated through the application of three comparative methods: the simple Hard Sphere Electrostatic model (HSE), the Brown and Wanner Theory (BWT) and the Correlation between Solubility and Complex stability constants of a metal ion (CSC). The latter method is the most empirical one, but it gives coherent results, in agreement with the few published experimental values, for all the possible aqua species of protactinium (Pa4+, Pa5+, PaO2+ and PaO3+). The selected thermodynamic data have then been used to predict the protactinium solubility in non complexing media of various pH and redox potential.
The influence of humic acids (HA) on the retention of thorium (IV) onto the surface of silica colloids is investigated. Thorium is considered as an analogue of tetravalent actinides (U, Np, Pu), except for the fact that it has no f electrons. Silica (SiO2) is chosen as a model surface because it is a component of many minerals and because of its weak HA sorption properties. Retention experiments are performed by batch procedure at constant ionic strength (I = 0.1M NaClO4), at various pH (2 to 9) and HA concentrations (1–100 mg/L). The sorption of Th(IV) onto colloidal amorphous silica is characterised using a surface complexation model. The ternary system (i.e. HA-Th-Silica) clearly shows the influence of HA on Th(IV) retention. This can lead to a strong reduction of the amount of Th(IV) sorbed onto silica in the presence of HA compared to silica colloids without HA, due to a predominant part of thorium present in solution as humic complexes. In a pH range where no organic coating onto silica occurs, there is a competitive reaction between Th(IV) sorption onto the silica surface and onto HA reactive functional groups. In this case, Schubert’s method is applied to obtain a global interaction constant for the Th(IV)-HA system. The large interaction constant values indicate a strong affinity of HA for Th(IV).
Enhanced mobility of radionuclides has been observed at several waste disposal sites; radioactive wastes have often contained strong, organic complexing agents as co-contaminants. Adsorption at mineral-water interfaces is one of the types of reactions by which radionuclides may become immobilized in the subsurface environment. For a contaminant metal introduced into the subsurface in organically-complexed form, such immobilization requires either adsorption of the intact complex or displacement of the contaminant metal from the complex. Comparison with complexation reactions in solution suggests that, in the tatter case, immobilization of the contaminant metal may be subject to kinetic limitations. A comparative discussion of the mechanisms of complexation reactions in solution and at surfaces serves as background for examination of laboratory studies of competitive- and co-adsorption and field studies of metal mobility.
The efficiency of Minor Actinides (MA) recovery in the DIAMEX process has already been demonstrated using High Active Raffinate (HAR). The next step aims at the demonstration of reprocessing from High Active Concentrate (HAC) as feed, in view of an industrial application. The volume reduction would reduce the size of the installation to be used and thereby the costs of the process. The first step towards the demonstration of a DIAMEX process using HAC is the production of the genuine solutions. In the hot cell facility of ITU (Institute for Transuranium Elements), a HAR solution has been prepared, from small scale PUREX reprocessing of MOX fuel, and successfully subjected to a concentration/denitration process to obtain HAC. A final concentration factor (CF) of about 10 and an acidity of 4 M were reached. In the experiment a precipitate mainly composed of Sr, Zr, Mo, Sn and Ba was formed. MA precipitation was not significant (< 0.001%).
The solubility of uranium(IV) hydrous oxide was measured at 25°C in NaClO4 solution containing Na2S2O4 as a reducing agent in the pH range from 12 to 14. The experiment was carried out from oversaturation at I = 0.5, 1.0 and 2.0 mol/dm3 (M). The solubility data were analyzed to obtain the hydrolysis constants (ßm) of U(OH)m(4-m). By taking the specific ion interaction theory (SIT) for ionic strength corrections and by using the solubility product log Ksp° = -53.93 ±0.20, the hydrolysis constants at I = 0, log ß5° <48.10 and logß6° ±48.95 ±1.01, were determined together with the ion interaction coefficients of U(OH)5- and U(OH)62-.
The hydrolysis constants of tetravalent uranium were determined by a solvent extraction method using thenoyltrifluoroacetone(TTA) and U-233. The distribution ratio of U(IV) was measured as a function of the pH, value in the aqueous phase at I = 0.1, 0.5 and 1.0, and was analyzed to obtain the hydrolysis constants (beta(m)) of U(OH)(m)((4-m)+) at the standard state (I = 0). By taking the specific ion interaction theory (SIT) for ionic strength corrections, the hydrolysis constants at I = 0 were determined to be beta(1)degrees = 13.71 +/- 0.31, beta(2)degrees = 26.12 +/- 0.21 and beta(3)degrees = 36.85 +/- 0.36, together with the ion interaction coefficients of UOH3+, U(OH)(2)(2+) and U(OH)(3)(+). The solubility product (K-sp) for the reaction of UO2.XH2O = U4+ + 4OH(-) + (x - 2)H2O was also calculated to be log K(sp)degrees = -53.93 +/- 0.20 by considering the hydrolysis constants.