Band 92, Heft 12 -

Hassium, element 108, was produced in the fusion reaction between 26 Mg and 248 Cm. The hassium recoils were oxidized in-situ to a highly volatile oxide, presumably HsO 4 , and were transported in a mixture of He and O 2 to a deposition and detection system. The latter consisted of 16 silicon PIN-photodiodes facing a layer of NaOH, which served, in the presence of a certain partial pressure of water in the transport gas, as reactive surface for the deposition of the volatile tetroxides. Six correlated α-decay chains of Hs were detected in the first 5 detectors centred around detection position 3. In analogy to OsO 4 , which forms Na 2 [OsO 4 (OH) 2 ], an osmate(VIII), with aqueous NaOH, HsO 4 presumably was deposited as Na 2 [HsO 4 (OH) 2 ], a hassate(VIII).

The separation of actinides and lanthanides is an important question in the treatment of spent nuclear fuel in the transmutation concept. To find an efficient and well functioning separation process it is necessary to study the chemistry of the elements in the two groups in different aqueous media. The stability constants of the nitrate complex formation with Pm, Eu, Am and Cm were determined using solvent extraction. The extraction was studied using the synergistic system of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine and 2-bromodecanoic acid in tert -butyl benzene. As the nitrate ion concentration in the aqueous phase was increased, a decrease in separation between actinides and lanthanides was seen owing to complex formation between the different elements and the nitrate ions.

The hydrolysis and interaction of Np(IV) and Pu(IV) with orthosilicic acid, Si(OH) 4 , were studied in 0.1–1.0 M ionic strength aqueous solutions. Spectrophotometry was used to study these reactions at about 10 –4 M Np(IV) and Pu(IV) concentrations. The first hydrolysis constants, K hydr , agree with the majority of earlier spectrophotometric and potentiometric data. The absorption spectra of NpOH 3+ and PuOH 3+ were obtained by spectral deconvolution. Reasons to explain the overestimation of K hydr obtained by other methods [by extraction of trace amounts of Np(IV) and Pu(IV) and by solubility] are discussed. Formation of the complexes NpOSi(OH) 3 3+ and PuOSi(OH) 3 3+ is demonstrated in the presence of 0.005–0.016 M Si(OH) 4 in the p[H + ] range 1.0–2.2 and 0.3–1.4, respectively. Measured values of equilibrium constants of the reaction M 4+ + Si(OH) 4 ↔ MOSi(OH) 3 3+ + H + at ionic strength I =1.0 are lg K 1 = 0.41±0.02 and 1.04±0.04, respectively, for Np(IV) and Pu(IV). The stability constants of the NpOSi(OH) 3 3+ and PuOSi(OH) 3 3+ complexes, recalculated to zero ionic strength, are lg β 1 0 = 11.2 and 11.8, respectively. The correlation between K hydr and K 1 , as observed for all earlier studied metal ions, also occurs for both Np(IV) and Pu(IV).

The reduction kinetics of Np(VI) by n -butyraldehyde in 30% TBP solution diluted with n -dodecane were analyzed by spectrophotometry. Based on the results of both n -butyraldehyde and nitric acid concentration dependences on the Np(VI) reduction reaction, the rate equation was obtained as –d[Np(VI)]/d t = k [ n -C 3 H 7 CHO] 0.8 [HNO 3 ] –2.0 [Np(VI)] t where k =(1.0±0.2)× 10 –3 M 1.2 min –1 at 294±1 K. The activation energy of the reaction was 76±5 kJ/mol.

The complex formation of U(VI) with phosphate and with fluoride has been studied at elevated temperatures (20–150 °C) and pressures (0.1–40 MPa) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Emission spectra and lifetimes of 5×10 –5 M uranium(VI) in 0.5 M NaClO 4 solutions in the presence and absence of ligand ions were measured as a function of the pH, ligand concentration, temperature and pressure. The emission intensities and lifetimes of uranium(VI) decreased rapidly with increasing temperature. In contrast, a pressure effect on the fluorescence properties was quite small. The fluorescence decay curves could be resolved into several fluorescent species. The temperature dependence of the lifetimes followed the Arrhenius law, and the activation energies were estimated for the phosphate and fluoride complexes. These results were compared with speciation calculations at several temperatures obtained by using the DQUANT equation and thermodynamic data in the literature. From these comparisons, each component of the fluorescence was identified as a complexed species or a free uranyl ion at several temperatures, indicating that the Arrhenius plot of fluorescence lifetime is an effective method for in-situ speciation of uranyl complexation at elevated temperatures.

Conditional and pH independent stability constants have been determined for U(IV) α-isosaccharinic acid (ISA) and gluconic acid (Gl) complexes, under anaerobic and carbonate-free conditions, from pH 3 to 14. The constants are needed for nuclear waste repository performance assessment purposes. The constants were obtained by developing an approach based on the solubility product of amorphous UO 2 ·2H 2 O. The derived pH independent log β values for U(OH) 4 ISA and U(OH) 4 Gl were 49±2 and 50±1 respectively.

The complex formation in the aqueous systems of uranium(VI) with glucose 6-phosphate (G6P) and fructose 6-phosphate (F6P) were studied using potentiometric titration, TRLFS, and EXAFS. Two complexes with a uranyl-to-ligand ratio of 1:1 and 1:2 for both sugars were observed. Complex stability constants were determined by potentiometric titration for both complexes to be log β 11 (G6P)=5.89±0.40, log β 12 (G6P)=9.45±0.08, log β 11 (F6P)=5.72±0.21, and log β 12 (F6P)=9.54±0.09. Stability constants could be determined with TRLFS under the specific experimental conditions only for the 1:1 complexes: log β 11 (G6P)=6.35±0.28, and log β 11 (F6P)=5.66±0.17. The TRLFS measurements results show the UO 2 G6P complex to exhibit no fluorescence properties. For this system, only a decrease of the fluorescence intensity with increasing ligand concentration was observed. For the UO 2 F6P system, a red shift of the fluorescence emission bands of about 8 to 9 nm compared to the free uranyl ion was observed. The fluorescence emission wavelengths of the UO 2 F6P complex were determined to be 483, 496, 518, 542, and 567 nm, and the lifetime of this complex is 0.13±0.05 μs. Uranium L III -edge EXAFS measurements at pH 3.5, 4.0, and 5.5 yielded a shortened U–O eq bond distance (2.30±0.02 to 2.37±0.02 Å), compared to the UO 2 2+ (H 2 O) 5 ion (2.40±0.02 Å), due to a monodentate coordination via the oxygen atoms of the phosphate group.

In the 1970s and 1980s, U.S. Department of Energy (DOE) conducted numerous studies on the fabrication of nuclear fuel particles using the internal gelation process. These amorphous kernels were prone to flaking or breaking when gases tried to escape from the kernels during calcination and sintering. These earlier kernels would not meet today´s proposed specifications for reactor fuel. In the interim, the internal gelation process has been used to create hydrous metal oxide microspheres for the treatment of nuclear waste. With the renewed interest in advanced nuclear fuel by the DOE, the lessons learned from the nuclear waste studies were recently applied to the fabrication of uranium kernels, which will become tri-isotropic (TRISO) fuel particles. These process improvements included equipment modifications, small changes to the feed formulations, and a new temperature profile for the calcination and sintering. The modifications to the laboratory-scale equipment and its operation as well as small changes to the feed composition increased the product yield from 60% to 80%–99%. The new kernels were substantially less glassy, and no evidence of flaking was found. Finally, key process parameters were identified, and their effects on the uranium microspheres and kernels are discussed.

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/H 2 and Ar/H 2 O-atmospheres using γ-ray spectroscopy. Polonium release in the temperature range of interest for technical applications is slow. Within short term (1 h) 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 H 2 O 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.

Synergistic extraction of Ce(III), Eu(III) and Tm(III) as a representative of lanthanides(III) with a mixture of picrolonic acid {1- p -nitrophenyl-3-methyl-4-nitro-5-pyrazolon (HPA)} acting as an acidic chelating agent and tributylphosphineoxide (TBPO) as a neutral ligand in chloroform from pH 2 buffer solution has been studied. The composition of the synergistic adduct has been determined to be M(PA) 3 ·2TBPO (M=Ce(III), Eu(III), Tm(III)). The effect of various anions and cations on the extraction of these metal ions has also been studied. Among the anions, fluoride, oxalate, citrate and cyanide ions masked the extraction, whereas Fe(III) and Cu(II) reduced the extraction to ∼90%. The formation constant, and separation factor from various metal ions has also been determined and discussed.

A new chelating polymer has been developed wherein Amberlite XAD-4 has been functionalized by coupling it with diethylmalonate after acetylation. The resulting resin has been characterized by IR spectral and microanalysis studies and has been used for preconcentrative separation of thorium(IV) in the presence of alkali, alkaline earth, transition elements and lanthanides. Various physico-chemical parameters influencing the sorption of thorium(IV) onto the polymeric matrix was investigated and optimized by both batch and column methods. Quantitative extraction of thorium(IV) was obtained in the pH range 6.0–8.0. The sorption capacity of the malonic acid functionalized resin is 19.28 mg per g of polymer with an enrichment factor of 500. Moreover, the system showed faster exchange kinetics for extraction of thorium(IV) thus resulting in quantitative enrichment at flow rates as high as 16.0 cm 3 /min using 0.2 g of resin packed column (7 mm dia). Five replicate determinations of 10 μg of thorium(IV) present in 2.5 dm 3 of sample solution gave a mean absorbance of 0.160 with a relative standard deviation of 2.54%. The detection limit corresponding to 3 times the standard deviation of the blank was found to be 0.2 μg dm 3 . The developed procedure has been successfully utilized for the estimation of thorium(IV) content of pure rare earth chloride solution collected from Indian Rare Earths Limited, Alwaye, India.

As a major requirement for adopting a well-defined quality system for our instrumental neutron activation analysis laboratory regular participation in the IAEA intercomparison exercises is carried out in routine. IAEA marine sediment (IAEA-433) as a proposed reference material has been studied and thirty elements have been determined employing appropriate irradiation, cooling and counting protocols using instrumental neutron activation analysis (INAA) technique. Employing the same protocols on IAEA SL-1 and IAEA 405 certified reference materials the method has been validated and our values show good agreement with the certified values predicting good accuracy. Miniature neutron source research reactor has been utilized for this work. The results for the IAEA-433 present good precision of less than 5% for Mn, Hf, Sm, Th, Al and Fe whereas for Rb, Tb, V, Se, Ga, Sn and Zn results are with comparatively poor precision ranging 10%–13%.

Samples of sand, stone and manufactured building materials collected from Karachi area have been analyzed for the primordial natural radionuclides 238 U, 232 Th and 40 K using γ-ray spectrometry. The uranium and thorium contents have also been determined by instrumental neutron activation analysis (INAA). The specific activities in these materials, having a radium equivalent activity less than 370 Bq kg –1 , when evaluated for radiological effects show that all materials meet the external γ-ray dose limitation of 1.5 mSv y –1 . The γ-ray spectrometric and INAA techniques complemented each other well in this study.

Iodine-124 ( T 1/2 =4.18 d) is an important radionuclide for preclinical research in positron emission tomography (PET). We describe an improved method to produce and extract 124 I from a solid [ 124 Te]TeO 2 target efficiently using the dry distillation technique. Our process is based on remote hot cell handling and was optimised to achieve efficiencies better than 90% with an average thick target yield of 9.0±1.0 MBq/μAh ( n =47, corrected for decay). The technology is safe and reduces the dose to the operator.