Band 90, Heft 3 -

Systematic studies on fission neutron spectrum averaged cross sections of some threshold reactions like ( n , 2 n ), ( n , p ) and ( n , α) on titanium were carried out using the activation technique in combination with radiochemical separations and high-resolution γ-ray spectroscopy. Special attention was paid to the formation 45 Ti via the 46 Ti( n , 2 n ) 45 Ti reaction since 45 Ti labeled compounds are potentially important radiopharmaceuticals. At a fast flux neutron density of 7.5 × 10 13 cm −2 s −1 and using 100% enriched 46 Ti target, 8.58 MBq saturation activity of 45 Ti per batch can be produced. Due to rather low activity and low specific activity the procedure is not feasible from medical application point of view.

The isotope 262 Db was produced by irradiation of a 248 Cm target with 106-MeV 19 F ions at the 15 MV MP Tandem accelerator of Orsay (France). The reaction products were continuously and rapidly transported with a KCl aerosol helium jet system to the chemistry setup. They were dissolved in HF medium and the solution was passed through three successive ion exchange columns, allowing a continuous high level purification of Db from actinides on a first cation exchange column, the isolation of Db on an anion exchange one, and the retention of the long-lived decay products of 262 Db (3.24 h– 254 Fm) on a second cation exchange column. Just after the end of irradiation, the decay products were desorbed from this column, purified and α-sources were prepared on carbon foil by electrospray. In 13 effective irradiation hours, 22 events corresponding to the α-decay of 254 Fm were recorded. Almost 70 atoms of 262 Db, produced in the reaction 248 Cm + 19 F were isolated in dilute HF medium. Like its homologues/analogues Nb, Ta and Pa, dubnium forms, with fluoride ions, negatively charged complexes which are strongly retained on anion exchanger.

A thermochromatographic separation was performed on plutonium from environmental soil samples. This procedure was investigated with the goal to measure low concentrations of plutonium by inductively coupled plasma-mass spectrometry (ICP-MS). The soil sample was chlorinated by thionylchloride as reactive gas at a temperature of 1400 K. The volatile chlorides were separated chromatographically and deposited in a temperature gradient tube filled with quartz grains. Results about the deposition behaviour of the elements were obtained. Two different formalisms based on the thermodynamic functions are used to describe the experimental data. One formula is used to describe the deposition behaviour of microscopic amounts of plutonium (adsorption), the other formula for macroamounts of the main matrix elements (desublimation). The calculated values are in a reasonable agreement with the experimental data. A determination of plutonium content was successfully made for a referenced sea sediment (IAEA-135) after the thermochromatographic sample preparation for ICP-MS.

Extraction of uranium from tissue matrix was studied using supercritical carbon dioxide containing modifier solvent. The extraction efficiency was investigated with carbon dioxide containing methanol, tri- n -octyl phosphine oxide (TOPO) in methanol and tri- n -butyl phosphate (TBP) in methanol as modifiers. The extraction behaviour of the UO 2 (NO 3 ) 2 · 2TOPO complex loaded on tissue was also investigated. Supercritical carbon dioxide modified with methanol alone was found to extract a maximum of about 76% uranium from tissue matrix.

The uranyl(VI) malonate complex formation was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 4 and an ionic strength of 0.1 M NaClO 4 . The uranium concentration was 5 × 10 −6 M at ligand concentrations from 1 × 10 −5 to 1 × −2 M. The measured fluorescence lifetimes of the 1:1 and 1:2 uranyl(VI) malonate complexes are 1.24 ± 0.02 µs and 6.48 ± 0.02 µs, respectively. The fluorescence lifetime of the uranyl(VI) ion is 1.57 ± 0.06 µs in 0.1 M perchloric media. The main fluorescence bands of the malonate complexes show a bathochromic shift compared to the uranyl(VI) ion and are centered at 494 nm, 515 nm and 540 nm for the 1:1 complexes and at 496 nm, 517 nm and 542 nm for the 1:2 complex. The spectra of the individual uranyl(VI) malonate complexes were calculated using a multi exponential fluorescence decay function for each intensity value at each wavelength, covering the entire wavelength range. Stability constants were determined for the complexes UO 2 C 3 H 2 O 4 ° (aq) and UO 2 (C 3 H 2 O 4 ) 2 2− from results of spectra deconvolution using a least square fit algorithm (logβ 1 ° = 4.48 ± 0.06, logβ 2 ° = 7.42 ± 0.06 or log K 2 ° = 2.94 ± 0.04). The results are compared with literature values obtained by potentiometric measurements.

Adsorption of uranium (U(VI)) from aqueous solutions on halloysite type clay was studied as a function of amount of adsorbent, initial concentration and pH. The values of adsorption data were fitted to Freundlich, Langmuir and Dubinin–Radushkevich (D–R) adsorption isotherms. The mean energy of adsorption was calculated as 5.91 kJ/mol from D–R adsorption isotherm. Lagergren and Bangham equation has been used for dynamic modelling of process and the rate constants of adsorption of uranium on halloysite type clay were calculated at 293, 313 and 333 K. In order to explain the mechanism of adsorption reaction, the rate constants were calculated at high and low uranium concentrations. Adsorption reaction was studied at 293, 303, 313, 323 and 333 K for halloysite type clay and also thermodynamic constants have been calculated. The results show that the adsorption reaction was endothermic and more spontaneous at high temperature.

Hydrolytic and radiolytic stabilities of a promising extractant, N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA), for actinides in high-level radioactive liquid waste from nuclear fuel reprocessing were investigated in air at room temperature. Hydrolysis by nitric acid was not observed, whereas radiolysis by gamma irradiation was notably observed. The radiolysis study showed that an amide-bond, an ether-bond, and a bond adjacent to the ether-bond tended to be broken by gamma irradiation, and dioctylamine and various N,N-dioctylmonoamides were identified as the main degradation products by GC/MS and NMR analyses. The G -value for degradation of neat TODGA was 8.5 ± 0.9, which value was higher than those for N,N′-dioctyl-N,N′-dimethyl-2-(3′-oxapentadecyl)-propane-1,3-diamide and N,N-dioctylhexanamide. It was obvious that n -dodecane, which was used for a diluent, had a sensitization effect on the radiolysis of these amidic extractants. In a TODGA– n -dodecane–HNO 3 system, the coexisting nitric acid showed an insignificant effect on the radiolysis of TODGA.

In connection with the production of 46.2 min 51 Mn via the 50 Cr( 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 * Mn II /Cr III , * Mn II /Cr VI and * Mn IV /Cr VI , the latter applying the co-precipitation of * Mn IV with Fe III 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 Al 4 · 50 CrCl 3 was developed as a new target. This allowed a quick dissolution after irradiation, thus enabling a fast separation of 51 Mn and its production on a MBq scale. A 1 h irradiation at 3 µA (wobbled beam) over an effective deuteron energy range of E d = 12.8 → 7.9 MeV yielded 107 MBq 51 Mn. Simultaneously formed nuclides of other elements, such as 38 Cl, 24 Na, 48 V and 51 Cr were quantitatively separated using the proposed procedure. Only the shorter-lived radioisotope 52m Mn, formed via the 52 Cr( d , 2 n ) 52m Mn reaction, was present at a low level of 2%, if the enrichment of 50 Cr was 95% (with ∼5% 52 Cr).

Separation of lithium and magnesium isotopes was investigated by chemical ion exchange with a manganese(IV) oxide using an elution chromatography. The capacity of manganese(IV) oxide was 0.5 meq/g. Two molar sodium acetate solution was used as an eluent. The heavier isotopes of lithium and magnesium were enriched in the solution phase, while the lighter isotopes were enriched in the MnO 2 phase. The separation factors were determined according to the method of Glueckauf from the elution curves and isotopic assays. The separation factor of lithium isotopes was 1.026. In addition, the separation factors of 24 Mg 2+ – 25 Mg 2+ , 24 Mg 2+ – 26 Mg 2+ , and 25 Mg 2+ – 26 Mg 2+ isotope pair fractionations were 1.012, 1.022, and 1.011, respectively. The isotope separation system in this work can be explained by the fact that the hydration and isotope mass effects are more significant.