Volume 93, Issue 12 -

A chemical separation procedure for Rf/Db is described which was applied to a long-lived decay product from the nuclear fusion reaction 48 Ca+ 243 Am. A 1.2 mg thick 243 Am target was bombarded by 247 MeV 48 Ca particles. The recoiling products were collected in a thick Cu catcher for about one day and then subjected to a chemical separation procedure that included an ion exchange from dilute HF solutions. Final samples were prepared on 30 μg/cm 2 thick polyethylene (PE) foils and counted in 4π-geometry for α-particles and spontaneous fission (SF) coincidences. The detector arrays were surrounded by 3 He detectors to also assay prompt neutrons. Decontamination factors from actinides of about 10 5 were achieved. Group 6 (W) to 14 (Pb) elements as models for their heavier homologues were shown to be separated from the Rf/Db fraction with more than 90%. In eight final samples, representing a total beam dose of 3.4 × 10 18 particles, 15 SF events were detected. The decay pattern points to a single component with a half-life of ≈32h, which shows a chemical behavior similar to the lighter homologues of group 4 and 5 elements.

The complexation of Am 3+ , Cm 3+ and Eu 3+ with EDTA has been studied at an ionic strength of 6.60 mol kg −1 (NaClO 4 ) and pcH 3.60 in the temperature range of 0 to 60 °C with a solvent extraction technique. The complex M(EDTA) − was formed with stability constant values (log β 101 ) at 25 °C between 15.9 and 16.1 which increased with increasing temperature. The complex formation enthalpies have been obtained from the temperature dependence of the stability constants. The large positive enthalpy and entropy changes are attributed to the considerably reduced water activity at such high ionic strength resulting in large positive contributions from the dehydration of the trivalent metal ions as compared to the smaller negative contributions from the M 3+ –EDTA 4− bonding interaction. The nature of the species of the EuEDTA complex formed at 6.60 mol kg −1 (NaClO 4 ) and pcH ≥3.60 was studied by time-resolved laser fluorescence spectroscopy and lifetime measurements. Between pcH 3.60 and 7.0, Eu(EDTA)(H 2 O) 3 − was formed while at pcH 9.0, Eu(OH)(EDTA)(H 2 O) 2 2− was present.

The complexation of Cm(III) and Eu(III) with dissolved silica was studied by solubility measurement and time resolved laser fluorescence spectroscopy (TRLFS) in basic solutions over a range of total silica concentrations and ionic strengths (NaNO 3 ). In initial experiments on the solubility of Eu(OH) 3 in silicate containing solutions we observed a rapid increase in the soluble Eu(III) concentration under basic conditions. The Eu(III)/Cm(III) silicate complexes that formed caused a significant increase of the hypersensitive 5 D 0 → 2 F 2 band around 615 nm relative to the non-hypersensitive 5 D 0 → 7 F 1 band at 592 nm for Eu(III). Further studies of Eu(III) and Cm(III) containing solutions showed a shift of the fluorescence spectral maximum from 594 nm to up to 607 nm for Cm(III) along with a significant increase of fluorescence intensities. The fluorescence lifetimes for Eu(III) species increased from 115 μs to 1.8 ms in 3.0 M and 5.0 M NaNO 3 , corresponding to full coordination, and from 68 μs to 202 μs for Cm(III) in 0.1 M NaNO 3 , consistent with the removal of 6–7 water molecules upon silicate complexation. The variations of the fluorescence intensity and the concentrations of the monomeric and polymeric silicates suggested that in basic silicate solutions, Eu(III)/Cm(III) mainly complexes with polysilicates.

Eight p -adamantylcalix[4]arene derivatives, bearing four CMPO-like functions [(CH 2 ) n NHC(O)CH 2 - P(O)Ph 2 ] at the wide ( 4a,b , n = 0, 1) or narrow ( 5a–c and 6a–c , n = 2–4) rims were synthesized for the first time. Studies of the extraction of americium(III) and europium(III) from 3 M HNO 3 solutions to organic phases (dichloromethane, m -nitro-trifluoromethylbenzene) showed: (i) The extraction ability for all the adamantylcalixarene ligands is much better than for their monomeric analogues – N -(1-adamantyl)-, N -(1-adamantylmethyl)- and N , N -(dibutyl)carbamoylmethyldiphenylphosphine oxides 7a, 7b, 8; (ii) The extraction percentage increases strongly with increasing length of the spacer for all types of ligands 4–6 , and best extraction results were found for 4b ( n = 1) and 5c ( n = 4); (iii) The separation coefficient D Am / D Eu for the investigated compounds did not exceed 2, which is close to the narrow rim CMPO calixarenes, studied earlier; (iv) Variation of the spacer length between CMPO groups attached to the 1,3- and 2,4-positions of the calixarene platform in 6 did not lead to appreciably improved extractants, neither with respect to the extraction abilities ( D ) nor to the selectivities ( D Am / D Eu ).

The conditional stability constants for trace-level concentrations of Pu(IV) complexing with citric and alginic acids were determined at pH 4 and an ionic strength of 0.1 M NaCl using an ion-exchange technique. The results of these experiments were analyzed with: 1) the graphical Schubert's approach, 2) a non-linear simulation of ‘Schubert’-type data, and 3) an affinity distribution approach to describe the alginic acid. Analysis of the results of ion-exchange data for Pu(IV)-citric acid systems using Schubert's method indicates the formation of a 1 : 1 Pu-citrate complex with a stability constant (log β 1,1 ) of 16.536 ± 0.015 at I = 0.1 M. Alginic acid exhibits a strong affinity for plutonium and, unlike citric acid, the experimental results were interpreted as a mixture of 1 : 2 and 1 : 3 Pu : alginic acid complexes using non-linear Schubert's analysis of ion-exchange data; average conditional stability constants (log β) of 13.479 ± 0.057 and 14.755 ± 0.305 at I = 0.1 M NaCl, respectively, were determined. The results from the ion-exchange experiments were also modeled based on a non-electrostatic, discrete ligand approach in which alginic acid is conceptualized as being composed of a suite of monoprotic acids, HL i , of arbitrarily-assigned p K a(i) values ( e.g. , 2, 4, 6 and 8). The experimental ion-exchange data were best described by postulating complexation reactions between Pu(IV) and the model ligands L 2 (p K a = 4) and L 3 (p K a = 6), forming the species Pu(L 2 ) 2 2+ and Pu(L 3 ) 3 + , indicating that the Pu(IV) binding by alginic acid occurs mainly through carboxylic groups under the experimental conditions studied.

Electrochemical and spectroelectrochemical has been used to investigate the behaviour of neptunium (VI) in 1 ∼ 8 M HNO 3 solutions. The electrochemical reactions of Np(VI) ions were found to occur quasi -reversibly. The formal redox potentials ( E °) for Np(VI)/Np(V) couples were determined to be +0.906, +0.908, +0.909, +0.902, +0.896, +0.895, +0.888, and +0.884 V ( vs . Ag/AgCl) for Np(VI) ions in 1, 2, 3, 4, 5, 6, 7, 8 M HNO 3 solutions, respectively. The reduction processes of Np(VI) ions were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from +1.10 to +0.60 V versus Ag/AgCl reference electrode redox couple for Np(VI) in HNO 3 solution have clear isosbestic points. These results indicate that the only reduction product of Np(VI) is Np(V), which is of considerable stability in HNO 3 solutions.

241 Am and 244 Cm were analysed from peat samples collected in Finland immediately after the Chernobyl accident. The separation method included co-precipitation, anion exchange and extraction chromatography. Activities of 241 Am and 244 Cm were measured by alpha spectrometry. The activity of Chernobyl-derived 241 Am varied between 0.0115 and 9.32 Bq/m 2 and that of 244 Cm from < 0.002 to 1.97 Bq/m 2 (reference date 1.5.1986). The origin of 241 Am in Finland is predominantly from atmospheric nuclear tests. However, the geographical distribution of Chernobyl-americium is uneven and depending on a location even 100% of 241 Am in peat originated from the Chernobyl accident. The deposition pattern of Chernobyl-derived 241 Am and 244 Cm resembles that of other refractory nuclides, such as 95 Zr, 141 Ce and 239,240 Pu.

An analytical method is described for the estimation of uranium concentrations, of 235 U/ 238 U and 236 U/ 238 U 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 235 U/ 238 U and 236 U/ 238 U isotope ratios and the average value amounted to 9.4 ± 0.3 MWd/(kg U).