Band 94, Heft 8 -

Employing the activation technique in combination with radiochemical separations and high-resolution γ-ray spectroscopy fission neutron spectrum averaged cross sections were measured for several ( n , p ) and ( n , α) reactions on isotopes of zirconium; our measurements constitute the first systematic study. The special interest was in the investigation of the 90 Zr( n , p ) 90 Y reaction for the production of no-carrier-added 90 Y in a nuclear reactor. At a fast neutron flux density of 7.5 × 10 13 cm −2 s −1 and an irradiation time of 120 h, using 100% enriched 90 Zr target 0.548 GBq of no-carrier-added 90 Y per batch could be produced. The method is thus suitable for medium-scale production of this radionuclide.

The thermal neutron cross sections of the reactions 126 Sn( n , γ) 127g Sn and 126 Sn( n , γ) 127m Sn were measured for the first time. A radiochemical carrier-free separation procedure of 126 Sn from high level liquid waste (HLLW) is based on the anion exchange and PbS co-precipitation. The ( n , γ) reactions on 197 Au and 55 Mn were used as monitors of thermal neutron flux in irradiation of 126 Sn samples. The radionuclides 126 Sn, 127g Sn, 127 Sb, 198 Au and 56 Mn were detected by HPGe γ-ray spectrometry. The experimentally obtained thermal neutron cross sections of the 126 Sn( n , γ) 127m Sn and 126 Sn( n , γ) 127g Sn reactions are: 126 Sn( n , γ) 127g Sn: σ g = 0.200 ± 0.039 b 126 Sn( n , γ) 127m Sn: σ m = 0.39 ± 0.10 b The total cross section of the reaction 126 Sn( n , γ) 127(m+g) Sn is 0.59 ± 0.14 b.

Activation techniques have been used to measure the excitation functions of proton induced nuclear reactions on natural copper from their thresholds up to 27.5 MeV. The beam current was measured using a Faraday cup with secondary electron suppression, and the radioactivity of the products was determined via high-resolution gamma ray spectrometry. The data were compared with the data recommended by the IAEA wherever it was possible. A comparison of the new excitation functions with the theoretical calculations reported in the literature was undertaken to check the order of agreement between them. Good agreement was found for the results of 63 Zn while the theoretical calculations overestimate the cross sections for 61 Cu and 62 Zn. The excitation function for the reaction nat Cu( p , x ) 61 Co was measured for the first time during this work. The integral yields of the radionuclides 62,63,65 Zn, 61 Cu and 61 Co were calculated. 63 Zn and 65 Zn are produced over the whole energy range of 3 to 27.5 MeV and the yield gets saturated above 20 MeV. 62 Zn, 61 Cu and 61 Co are produced at relatively high energies and have integral yield values between those of 63 Zn and 65 Zn. The relatively high yield of 62 Zn is useful for the production of 62 Zn/ 62 Cu generator system.

Alpha decay half-life of 244 Pu has been re-determined using thermal ionization mass spectrometry for atom ratios measurements and alpha spectrometry for alpha activity ratios measurements. Two different samples of enriched 244 Pu were used and the 244 Pu half-life was determined using 240 Pu and 242 Pu isotopes as reference nuclides in the relative activity method. A value of (8.12 ± 0.03) × 10 7 yr is recommended for the half-life of 244 Pu based on the present data. This value is of high precision and accuracy compared to the two data reported in 1966 and 1969 with significantly larger uncertainties.

The half-life of 132 I was determined using a HPGe detector by place-relay method; calibrating efficiency was avoided by counting alternately at different places. In order to simplify the treatment of data, the realtime of every counting interval was set the same. Two ways, iteration and translation, were adopted to deal with the data. The obtained half-life value of 132 I was (2.283 ± 0.002) h which has been checked and proven to be credible.

A process of step-wise complexation of group-4 elements Zr, Hf, and Rf in H 2 SO 4 solutions has been considered theoretically. Relative values of the free energy change of the M(SO 4 ) 2 (H 2 O) 4 , M(SO 4 ) 3 (H 2 O) 2 2− and M(SO 4 ) 4 4− (M = Zr, Hf, and Rf) formation reactions from hydrated and partially hydrolyzed cations have been calculated using the fully relativistic density functional theory method. They proved to be very similar for reactions of Zr and Hf. At low H 2 SO 4 concentrations, Hf should, however, have a slight preference for the complex formation, especially, when hydrolysis takes place, while with increasing H 2 SO 4 concentration and decreasing hydrolysis, the trend should be Zr > Hf. According to the results, Rf should exhibit a weaker tendency to complex formation than Zr and Hf at the entire range of acid concentrations, i.e. , for all types of complexes. Thus, the predicted trend is Zr > Hf ≫ Rf. The same trend is also found for the formation of R 4 M(SO 4 ) 4 , where R is a monovalent cation. Accordingly, the trend in the K d (distribution coefficient) values in anion-exchange separations of group-4 elements should be: Zr > Hf ≫ Rf. The obtained trend for Zr and Hf is in agreement with literature data on extraction of these elements in macro-concentrations from sulphuric acid solutions and with recent experiments on extraction of single species by TOA in toluene using the SISAK technique.

Alkali metal uranyl chloride (M 2 UO 2 Cl 4 (M = Na or Cs)) was dissolved in 1-butyl-3-methylimidazolium chloride (bmimCl) and the redox behavior of uranyl ion present in the resultant solution was investigated by cyclic voltammetry at 343 K. The cyclic voltammogram consisted of a reduction wave occurring at the peak potential of −0.85 V, due to the reduction of U(VI) and two oxidation waves occurring at the peak potentials of −0.6 V and +0.2 V. Controlled potential electrolysis of uranium(VI) loaded bmimCl gave a black deposit, which was characterized as uranium oxide by EDXRF and XRD analysis. Extraction of uranium(VI) from nitric acid medium by 0.05 M tri- n -octylmethylammonium chloride (TOMAC) in chloroform was studied and the cyclic voltammogram of uranyl ion present in the extracted phase exhibited a single reduction (−0.8 V) and an oxidation wave (0.06 V) at 298 K. Controlled potential electrolysis of uranium(VI) loaded TOMAC at −1.0 V also gave a black uranium oxide deposit similar to that observed in the previous case. The results indicated that uranyl ion in organic phase undergoes a single step two electron quasi-reversible reduction at the working electrode, which can be conveniently exploited for the direct recovery of uranium from the spent fuel or from high level liquid wastes.

Within the framework of studies concerning the migration of radionuclides in a potential nuclear waste disposal host rock, the retention properties of clayey materials towards Sn(IV) and Pu(IV) are approached. Chemical sorption is quantified with the partitioning coefficient K d , whose value is dependent on the physico-chemical conditions. Four argillites are selected from three different deep boreholes at Bure to characterise the retention of Pu(IV) and Sn(IV) in eight waters close to the interstitial solution. No differences in major mineralogical composition distinguished these argillite samples. However, significant differences in retention properties of these argillites in the same water towards Sn, could be attributed to minor phases not identified by DRX. Retention of Sn or Pu is not sensitive to weak physico-chemical conditions variations. E h conditions were imposed in the stability domain of Pu(IV). An auxiliary redox couple was tested and its impact on the results is briefly discussed. Sorption reversibility is verified for Sn(IV) and Pu(IV).

Th(IV) is considered herein as a chemical analogue of other actinides (IV). Effect of pH, ionic strength and humic acid/fulvic acid concentrations on the sorption of thorium(IV) to MX-80 bentonite was studied by batch technique. The sorption isotherms were acquired by varying pH in the range of 0.5–12 and FA/HA concentration in the range of 2–20 mg/L. The results indicate that soil fulvic acid has higher carboxylic content than humic acid, and has stronger positive influence on the sorption of Th(IV) on bentonite at low pH values than humic acid. The increase of FA/HA concentration results in a slight increase of Th(IV) sorption on FA/HA coated bentonite. The results of no drastic effect of different addition sequences of FA/HA and Th(IV) to bentonite suspension on Th(IV) sorption in the ternary system HA/FA-Th(IV)-bentonite indicate that both the Th(IV)-HA/FA complexation and HA/FA-bentonite sorption do not affect the sorption of Th(IV) on HA/FA coated bentonite obviously. The samples were also measured by SEM method and the results show that the surface properties of different samples are different.

The radionuclide 99 Tc is one of the fission products of spent nuclear fuel. The chemical forms of this element depend primarily on the pH and E h of the environment. The aim of this study was to describe the sorption of the pertechnetate anion onto bentonite under anaerobic conditions, which accurately simulate the environment of a deep repository. Several additives were tested to determine whether they increase the retention of 99 Tc on this material — Fe, FeS, Fe 3 O 4 and activated carbon. It was found that it is very difficult to create the same conditions present in the deep repository in the laboratory, which is why the reduction of the pertechnetate anion to its lower oxidation state (Tc(IV)) was not achieved. The retention of the pertechnate anion on bentonite is very low ( K D ∼1 mL/g), the uptake of the pertechnetate anion onto bentonite was achieved by the addition of suitable additives to the bentonite mixtures e.g. activated carbon, Fe and FeS ( K D ∼102–103 mL/g). Various chemical forms of technetium were obtained in the solution, dependant on the various reaction mechanisms of the pertechnetate anion. Fe and FeS enabled the reduction of the pertechnetate anion to its lower oxidation state in the form of insoluble TcO(OH) 2 or TcO 2 · n H 2 O, physical sorption is the dominant mechanism with activated carbon.

Sorption of Cd(II) ions on Haro river sand has been studied using radiotracer technique. The effects of pH and acid concentrations on the sorption were studied. The sorption increases with pH, reaches a maximum at pH7 and decreases at higher pH values. With acids, it was found that sorption decreases with increasing acid concentration, and for more oxidizing acids sorption was less. Kinetic studies indicate that mostly intra particle diffusion occurs with first order rate constant of 18.45 × 10 −2 min −1 . The sorption data follow the Freundlich and Dubinin–Radushkevich (D–R) isotherms. In addition to the radiotracer method, voltammetric technique was applied and the results by the two techniques are in good agreement. The sorption free energy value indicates that adsorption process is chemisorption. The effect of temperature was studied and values of Δ H , Δ S and Δ G for Cd(II) have been calculated which are 20.15 kJ mol −1 , 74.04 J mol −1 K −1 and −1.754 kJ mol −1 . Adsorption of Cd(II) on Haro river sand is endothermic, spontaneous and entropy driven. The effect of different anions and cations at different concentrations was studied. Levels of cadmium have been monitored in water and sediments.

3′[ 18 F]Fluoro-3′-deoxy-thymidine ([ 18 F]FLT) (III) has been discussed to be a promising tracer for assessing tumor proliferation. In order to perform clinical studies for evaluating [ 18 F]FLT a simplified labeling procedure was developed using 2,3′-anhydrothymidine with benzoyl as a protecting group in the 5′-position (I). In DMSO the labeling yield was 46% at 160 °C in 10 min. Hydrolysis was efficiently performed with 0.25% NaOH at room temperature within 10 min. The labeling procedure was transferred to a remote controlled synthesis module allowing the production of [ 18 F]FLT in high activities. The overall radiochemical yield was 18.1 ± 5.4% ( n = 55) with absolute yields of 9.2 ± 2.6 GBq of [ 18 F]FLT at EOS ready for injection (60 min after EOB; irradiation parameters: 35 μA, 60 min) and specific activities of 100–220 GBq/μmol. A convenient cartridge method for metabolite analysis was developed and validated versus HPLC showing that after 90 min 69.0 ± 7.0% of the radioactivity in plasma (less than 20% of initial radioactivity) was unchanged [ 18 F]FLT (26 patients with various tumors).

Due to interesting physical properties and wide availability of thallium-201 as a SPECT radionuclide, the idea of incorporation of this nuclide into biologically active compounds was targeted. Thallium-201 ( T 1/2 = 3.04 d) in Tl + form was converted to Tl 3+ cation in presence of O 3 in 6 M HCl controlled by RTLC/gel electrophoresis methods. The final evaporated activity was reacted with bleomycin in normal saline to yield [ 201 Tl]BLM at room temperature after 0.5 h (radiochemical yield > 99%) followed by HPLC analysis. The studies showed that thallic ion is mostly incorporated into bleomycin A 2 while other species in the pharmaceutical sample almost remain unlabeled. Radiochemical purity of more than 99% was obtained using RTLC, HPLC with specific activity of about 7 Ci/mmol. The stability of the tracer was checked in the final product in presence of human serum at 37 °C up to 3 d. The tracer accumulated in tumors of fibrosarcoma-bearing mice after 72 h.

A new method of separation of uranyl ions from di-, tri- and tetravalent cations such as thorium, zirconium, cerium(IV) and/or lanthanides(III) involving phosphoric acid medium is described in this paper. The process is based on the difference of solubility between various phosphates: M 2 (PO 4 ) 2 (HPO 4 )·H 2 O, M(HPO 4 ) 2 ·H 2 O, M(OH)PO 4 (where M is a tetravalent cation) or APO 4 · n H 2 O (where A is a trivalent cation) on the one hand, and the uranyl phosphate pentahydrate (UO 2 ) 3 (PO 4 ) 2 ·5H 2 O, on the other hand. Taking into account the associated solubility constants, the conditions of separation were calculated then experimented for a mixture of Th 4+ , Ce 4+ (as a plutonium surrogate), Zr 4+ , La 3+ , Ba 2+ , Sr 2+ and UO 2 2+ . Tetravalent and trivalent cations phosphates were precipitated in 2 mol L −1 nitric acid medium while uranyl ion and divalent cations remained in the solution. In a second step, (UO 2 ) 3 (PO 4 ) 2 ·5H 2 O was precipitated at pH ≈ 1.5 and thereby separated from divalent cations present in the solution.

Determination of iron(III) by substoichiometric extraction with 2-methyloxine into n -butanol is being reported. The method has been applied for the determination of the metal in several analyzed samples like Mn-bronze, Al-bronze and dolomite.

For lanthanides and actinides, nitrate complex formation is an important factor with respect to the reprocessing of nuclear fuels and in studies that treat partitioning and transmutation/conditioning. Different techniques, including microcalorimetry, various kinds of spectroscopy, ion-exchange and solvent extraction, can be used to determine stability constants of nitrate complex formation. However, it is uncommon that all lanthanides are studied at the same time, using the same experimental conditions and technique. The strengths of the complexes are different for lanthanides and actinides, a feature that may assist in the separation of the two groups. This paper deals with nitrate complex formation of lanthanides using a solvent extraction technique. Trace amounts of radioactive isotopes of lanthanides were produced at the TRIGA Mainz research reactor and at the Institutt for Energiteknikk in Kjeller, Norway (JEEP II reactor). The extraction of lanthanide ions into an organic phase consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine, 2-bromodecanoic acid and tert -butyl benzene as a function of nitrate ion concentration in the aqueous phase was studied in order to estimate the stability constants of nitrate complex formation. When the nitrate ion concentration is increased in the aqueous phase, the nitrate complex formation starts to compete with the extraction of metal ions. Thus the stability constants of nitrate complex formation can be estimated by measuring the decrease in extraction and successive fitting of an appropriate model. Extraction curves for La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho and Er were obtained and stability constants for their nitrate complex formation were estimated. Tb, Tm, Yb and Lu were also investigated, but no stability constants could be determined. The distribution ratios for the metal ions at low nitrate ion concentration were obtained at the same time, showing the effect of lanthanide contraction resulting in decreasing extraction along the series. A clear tetrad effect in the lanthanide group was also found.

The synergistic mixture comprising picrolonic acid (HPA) and benzo-15-crown-5 (B15C5) in chloroform has been used for the extraction of Nd 3+ , Tb 3+ and Lu 3+ as representatives of lanthanide(III) ions from pH 1-2 solutions having ionic strength of 0.1 mol l −1 (K + /H + , Cl − ). The composition of the extracted species has been determined as M(PA) 3 ·nB15C5 where M is Nd, Tb and Lu and n = 1 or 2. The acid dissociation constant (p K a ) has been evaluated to be 2.52 ± 0.01. The influence of various anions and cations on the extraction of these lanthanide(III) ions has also been studied and only oxalate and thiosulphate among the anions and Cu 2+ , Fe 3+ , Zn 2+ and Ni 2+ among the cations have some deleterious effect. The extraction equilibrium constants have been evaluated and discussed.

Electron beam irradiation is a known advanced oxidation process that is studied in the literature to examine the possibilities of pollutant removal from waters. In the present work, a common pollutant, phenol, was chosen as model molecule to investigate the capability of a simple reaction system to predict the influence of certain parameters on the efficiency of the electron beam process. This model is based on the main reactions occurring during the irradiation of aqueous solutions of phenol. It was found to simulate suitably the effect of the dissolved oxygen and of the initial concentration on the abatement of the molecule during the irradiation. Various irradiation experiments were also performed by modifying the mode of the dose deposition. The results showed that, for a given applied dose, the multiplication of the passages under the electron beam significantly improves the abatement of phenol (20%). The oxygenation of the solution and the mathematical expression of the evolution of the pollutant concentration with the radiation dose partly explain this improvement.