70 RADIOCHEMISTRY, STABLE ISOTOPES, NUCLEAR ANALYTICAL METHODS, CHEMISTRY IN GENERAL A CHEMICAL SEPARATION SCHEME FOR 24Na - A DECAY PRODUCT OF THE CLUSTER RADIOACTIVITY OF 233U Barbara Bartos, Aleksander Bilewicz PL9902223 233U is theoretically expected to decay by the 24Ne and impregnated with HDEHP. Then tracers of 22Na and 25Ne cluster emission leading to 208-209Pb, with a 224Ra with decay products were added at the top of the predicted partial half-life being in the range 3 x 1016 - column. The effluent from the teflon-HDEHP column 3 x lO17 y. Price et al. [1] in a 582 days experiment, was passed through three ion-exchange columns in using a track-recording phosphate glass detector regis- series. The first column was filled with Dowex 50Wx8 tering heavy ions emission from a thin 233U film. From and the second with cryptomelane-type hydrous the experiment, the measured partial half-life was 2 x manganese dioxide. Both columns were predicted to 1017 y. Our calculations show that 2 g of thorium efficiently remove the decay products of 233U such as should contain, in equilibrium, about 100 atoms of 225Ac, 225Ra, 213Bi and 209Pb. The third column was 0.5 Wl HNO3 Fs teflon impregnated HDEHP Fig. 1. Flow scheme of the separation of micro-amounts of sodium from weight quantities of uranium. 24Na (tic = 15.0 h) due to the (J decay of 24Ne. The packed with a composite ion exchanger containing goal of the present work was to separate a few tens of polyantimonic acid, which sorbed selectively the Na+ the 24Na nuclides from about 2 g of 233U and to ions. The third column was placed inside the cavity of determine in this way the efficiency of the decay the detector. The system was tested in a continuous 233U- 209 long time experiment. The sodium yield was always To achieve this goal we have devised a separation greater than 95%. The decontamination factors were scheme of submicro-amounts of sodium from 2 g of greater than 105 for uranium, 224Ra, 2l2Pb and 2l2Bi. uranium and its decay products (Fig.l). Simulation experiments were made with natural uranium and Reference 224 212 212 22 Ra, Pb, Bi and Na labels. Uranium nitrate [1]. Price P.B., Moody K.J., Hulet E.K., Bonnetti R., Migliorino C: was loaded on a column filled with teflon fine grains Phys. Rev. C, 43, 1781 (1990). FRACTIONATION OF YTTERBIUM ISOTOPES IN THE Yb(III)-ACETATE/Yb- AMALGAM SYSTEM. A SEVEN ISOTOPE TRIAL Wojciech Dembinski, Marek Poninski, Rudolf Fiedler17 11 PL9902224 Safeguards Analytical Laboratory, IAEA, Vienna, Austria Continuing our studies [1] on ytterbium isotope we determined the unit separation factors for all Yb separation in the Yb(IlI) acetate/Yb amalgam system isotopes. The exchange reaction is: RADIOCHEMISTRY, STABLE ISOTOPES, NUCLEAR ANALYTICAL METHODS, CHEMISTRY IN GENERAL 71 m 172 172% Yb(Ac)3+ Yb(Hg) <-> '"Yb(Ac)3 isotopes. The even odd effect, SO/E, as defined by The unit separation factor is defined as Nishisawa et al. [2], is visible only when the triad m 172 m 172 171,174,176 yb is taken int0 account. The value of eO/E for q = ( Yb/ Yb)Hg/( Yb/ Yb)ac where m means mass 171 number 168,170,171,173,174,176. The unit separation Yb is -0.00052. This value is to be compared with -0.00075 obtained in our previous measurement [1]. gain is 6 = q - 1 « ln(q). The isotopic analysis was 173 performed using a mass spectrometer with a multi- The even-odd effect of Yb, if exists, is covered by collector system (Finnigam MAT262). The precision error of measurement. of the measured isotopic ratio was 0.07% (1SD) or An interesting sequence of data is observed when better. the series of even-even pairs (Am = 2) is considered. The results are shown in Figure. The data for I68Yb The values of the separation gains are O.OO13±5% for 172/174 is excluded because an unexpectedly high value of i7o/n2Ybi 00010±5% for Yb and 0.0014+7% for 174/176 separation factor was found. This finding, will be Yb. The differences are probably related to the discussed later. nuclear field shift addend (sfS) in the total chemical 0.15 isotope effect. The isotope shifts observed in atomic spectra of ytterbium support such conclusion. As it is 0.10 known [3] the optical isotope shift of ytterbium is mostly due to the field shift (the mass shift can be 0.05 neglected) and is expressed by a change in the nuclear \ » 0.00 mean square radius. The respective values of S^) for the series mentioned above are 0.120 frn2 for Z -0.06 \ """V), 0.034 fm2 for 172/1748(r2), and 0.089 fm2 for l74/1768<r2>. It is to be noted that the chemical as well as "" -0.10 the optical effect of the middle pair, 172/174Yb, was -0.15 \ found to be lower than the effects of the lighter and heavier pairs. If it is so, a general approximation, -0.20 \ which suggests that the separation factor is propor- tional to the mass difference, is neither correct for -0.26 even-odd isotope pairs nor for even-even isotope pairs. 170 171 172 173 174 175 178 Fig. Separation factors of Yfa isotopes. References The value of the unit mass separation factor, eU; [1]. Dembiiiski W., Poniriski M., FiedJer R.: Sep. Sci. Techn., 33, defined as the mean of the even isotope separation 14,2101-2112(1998). factors (excluding 168Yb) was found to be 0.00059 and [2]. Nishisawa K., Nakamura K., Yamamoto T., Masuda T.: Solv. Extr. Ion. Exch., 12, 5, 1073-1084 (1984). was nearly the same as the experimental unit mass [3]. King W. H.: Isotope shifts in atomic spectra. Pergamon Press, separation factor calculated for the series of six New York-London 1984, pp. 142-143. HYDRATION AND SOLVATION OF LEAD(II) ACETYLACETONATE AND THE COORDINATION NUMBER OF LEAD(II) Jerzy Narbutt A great variety of coordination numbers (CN) of Pb" observation was, however, not explained and little and structures of its complexes have been reported [1], work has appeared subsequently, in particular that depending on the character of the 6s2 electrons. The focused on hydration and solvation of lead(II) large ionic radius of Pb" results from the lone electron complexes. pair occupying 6s orbital, but the radius decreases to The aim of the present work was to explain, why IV a value compared with that of Pb when the pair bis(acetylacetonato)lead(II) is relatively easily extracted enters a hybrid orbital and becomes stereochemically from aqueous solutions to organic solvents, specifical- active. Solvent extraction provides evidence for ly, whether its good extraction can be related to the hydration and solvation of metal complexes in character of the lone electron pair (is it stereo- solution and makes it possible to evaluate the extent of chemically active or non-active?). In fact, there are no their coordinative unsaturation (if any). This in turn data in the literature on the molecular structure of allows us to conclude on CN and the radius of the Pb(acac)2 [3]). central metal ion. Shigematsu and Tabushi [2] pointed To reach the goal, thermodynamics of water - out that extraction of Pb(acac) was higher than 2 toluene partition of Pb(acac)2 was investigated and expected from the large ionic radius of Pb". That discussed in terms of hydration of the chelate in the.