Band 88, Heft 1 -

Short-lived nuclides of iodine produced in the proton-, 12 C- and 19 F-induced fission of 235 U, 237 Np and 238 U were separated with a rapid chemical separation system SISAK. Relative yields of the nuclides were determined by γ -ray spectrometry to obtain the isomeric yield ratios of 134m I/ 134g I and 136m I/ 136g I. Angular momenta of the fission fragments, 134 I and 136 I, were derived from the measured isomeric yield ratios by the spin-dependent statistical model. In the light- and heavy-ion fission, variation of the observed angular momenta can be explained by the excitation energies of the fissioning nuclei and the spherical shell structure with N = 82.

The complexation of humic acid with Cm(III) and Am(III) is studied in the neutral pH range from 6 to 10 in 0.1 M NaClO 4 under Ar-atmosphere. Cm(III) and Am(III) species are characterized and quantified by time-resolved laser fluorescence spectroscopy (TRLFS) and UV/Vis absorption spectroscopy, respectively. The formation of ternary humate complexes, i.e. hydroxo-humate species, is ascertained besides the well known binary complex AnHA(III) (An = Cm(III), Am(III)) by spectroscopic speciation in aid of radiometric quantification. The pH dependent change in concentrations of individual Cm(III) and Am(III) species corroborates ternary humate complex formation: An(OH)HA(II) and An(OH) 2 HA(I), with stability constants evaluated to be log β 111 = 12.82 ± 0.11 and log β 121 = 17.53 ± 0.13 for Cm(III) and log β 111 = 12.71 ± 0.17 and log β 121 = 17.40 ± 0.21 for Am(III). The formation of ternary humate complexes culminates in the strong interaction of trivalent actinide ions with humic acid in the neutral pH range as compared to the binary complexation alone. The results are compared with a previous study on the Cm(III) interaction with humic colloids in a real groundwater system.

The complexation of uranium(VI) with humic acid was studied at pH 4 and 5 in 0.1 mol/l and 4.10 -3 mol/l NaClO 4 by indirect speciation methods, i.e., electrophoretic ion focusing (EIF) and anion exchange (AE). The concentration range investigated was from 10 -8 mol/l to 5 · 10 -6 mol/l for the uranyl ion and from 1 to 2.5 mg/l for the humic acid. The experimental data obtained by AE are well described by the complexation reaction involving the charge neutralization of the uranyl ion with two exchanging sites of humic acid. The complexation constant calculated by taking the loading capacity values into account is found to be log β = 6.08 ± 0.15. Concerning EIF, an interfering interaction between the humic acid and U(VI), occurring under the effect of the electric field, is evident and makes this separation technique not well suitable for the investigation of the U(VI):humic acid system.

A method is described for determining binary data for electrolytes from a study of a ternary mixture. The method is based on the concept of thermodynamically simple solutions and on water activity measurements. An application is described in which binary data for plutonium(IV) nitrate are determined from a ternary mixture of Pu(NO 3 ) 4 , HNO 3 and H 2 O. This novel application allows the thermodynamic behavior (activity coefficient) to be defined for a fictive solution of plutonium(IV) nitrate in water; the solution is ''fictive'' in that it does not correspond to physical reality, given that Pu(IV) is insoluble. The results can be used to calculate the activity coefficient of the electrolyte Pu(NO 3 ) 4 in any type of mixture containing nitric acid and other electrolytes for which the binary data are known.

The extraction behaviour of uranium(VI) and thorium(IV) from nitrate solutions has been investigated using Cyanex 923 (TRPO) in xylene as an extractant. The extraction data have been analyzed by both graphical and theoretical methods by taking into account complexation of the metal ion in the aqueous phase with inorganic ligands and all plausible complexes extracted into the organic phase. The results demonstrate that these metal ions are extracted into xylene as Th(NO 3 ) 4 · 2 TRPO and UO 2 (NO 3 ) 2 · 2 TRPO. The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis. Infrared spectral data of the extracted complexes have been used to further clarify the nature of the complexes. The selectivities between these metal ions were evaluated and compared with commercially important extractants like tri-n-butylphosphate (TBP).

The electrochemical control of the binding of metallic ions (actinides and a lanthanide) by redox active polyaniline resin, i.e., polyaniline doped by polystyrene sulfonate (Pani/PSSO 3 ), has been studied. Electrochemical and nuclear techniques (cyclic voltammetry, α -counting, Rutherford backscattering) have been used in order to characterize the exchange of thorium, lanthanum and uranium cations, particularly in terms of reversibility and efficiency. This electrochemical process has been compared with the chemical one promoted merely by pH variation, and the efficiency of the two methods has been discussed for each type of cation.

The specific activities of 238 U, 232 Th and 40 K in soil and shore sediments from the Mediterranean Sea Coast of Alexandria have been determined using direct gamma spectrometry with a HP-Ge detector and absorbed dose rates in air were calculated. The specific activity of 238 U was determined by laser fluorimetry after applying a radiochemical separation. The specific activities of 238 U, 235 U, 234 U, 238 Pu and 239+240 Pu were determined using an alpha spectrometer based on surface barrier detectors after applying sensitive radiochemical procedures. The specific activities of 238 U obtained by the three techniques were compared. The isotopic ratios 234 U/ 238 U and 238 Pu/ 239+240 Pu were calculated for evaluation of the geochemical behavior of the nuclides. Plutonium concentrations were compared with some reported values in other different marine ecosystems.

Radiochemical results ( 234 U, 238 U, 226 Ra and 228 Ra activities; 234 U/ 238 U, 228 Ra/ 226 Ra and 226 Ra/ 238 U activity ratios) are reported for 31 drinking water samples collected from 8 wells, 12 hot mineral springs, 5 cold springs, and 6 tap water samples. Activities of the Ra isotopes were measured by gamma spectrometry using a low background and high efficiency well type germanium detector. The U isotopes were counted in an alpha spectrometer. The results show that 238 U activity varies between 4.46 and about 308 mBq l -1 in wells, 0.59 and 17.88 mBq l -1 in hot springs, 2.19 and 3.21 mBq l -1 in cold springs, and between 2.5 and 15.70 mBq l -1 in tap water samples. 234 U/ 238 U activity ratio is generally higher than 1 which is the equilibrium activity ratio value in closed systems. It varies in the ranges 0.79-2.11 in wells, 0.97-7.39 in hot springs, 2.53-8.30 in cold springs, and 1.14-3.35 in tap water. Unlike well waters, spring waters show low 238 U activities and high 234 U/ 238 U activity ratios. The highest activity of Ra measured in hot mineral water samples is about 150 and 352 times higher than the highest activity of Ra found in well waters and in cold springs, respectively. 226 Ra/ 238 U activity ratios are in the ranges: 0.07-1.14 in wells, 1.79-2115 in hot springs, 0.86-4.79 in cold springs, and 0.18-5.61 in tap water samples. The data are similar to those published for other regions of the world.