RAD1OCHEMISTRY, STABLE ISOTOPES, NUCLEAR ANALYTICAL METHODS, CHEMISTRY IN GENERAL 59 COMPARISON OF SAMARIUM AND YTTERBIUM ISOTOPE EFFECTS IN ACETATE/AMALGAM SEPARATION SYSTEM Wojciech Dembiriski, Marek Poninski, Rudolf Fiedler1' 11 International Atomic Energy Agency, Safeguards Analytical Laboratory, Seibersdorf, Austria i o Continuing our studies on the relation between the sumably for the same reason the even-odd and even- IS isotope effect and the isotope mass, we have frac- -even effects in a series of samarium are not so ex- ^8 tionated the samarium isotopes by means of the posed as in the ytterbium series; however a signifi- exchange reactions between acetate complexes of cant asymmetry in the position of 152Sm and 149Sm Sm(III) in the solution and Sm(0) in the amalgam: can be announced. H L L H Sm(Ac)3 + Sm(Hg) ** Sm(Ac)3 + Sm(Hg) Of interest is the difference in the behavior of the where H and L - heavier and lighter isotopes. lightest isotopes of both the elements: 168Yb and The chemical procedure of the fractionation was Sm. The value of separation gain of 168Yb was similar to those applied in our studies on the sepa- found to be unexpectedly high (18xlO'4) in respect to ration of the isotopes of ytterbium [1]. the separation gains of the heavier isotopes (Fig.2) The isotopic analysis was performed using a mass while the value of separation gain of 144Sm is close to spectrometer with a multicollector system (Finnigam MAT262). In order to eliminate the mass fractiona- 1.00 tion effect the method of total evaporation of the o.ao sample was applied [2]. The precision of the mea- I sured isotopic ratio was 0.07%(lSD) or better. 0.60 It was found that the light isotope of samarium, likewise the light isotopes of ytterbium, are frac- § Q4°- — — — tionated into the amalgam phase. The measured values of unit separation gains as <£ 0.20- a function of the isotope mass number are shown in < Fig.l. The unit separation gain is here defined as 0.00 4 *-> e= q-l«ln(q) m 149 m(l) 149 •0.20- — where q=( (')Sm/ Sm)Hg)/( Sm/ Sm)Ac and - — m(i) - the mass numbers: 144, 146, 147, 148, 150, 152,154. -0.40 167 168 169 170 171 172 173 174 175 176 177 Fig.2. Unit separation gains of Yb isotopes, sd is standard devia- tion of the mean. the mean of the series (Fig.l). It is to be noticed that the unexpectedly high value of separation gain was recently also revealed for the lightest stable isotope of gadolinium 152Gd. It was discovered in the course of isotope separation in the extraction system with dicyclohexano-18-crown-6 [4]. The unit mass separa- tion factor of 152Gd was found to be three times greater (3.15xlO3) than the mean for the heavier iso- 3 topes 154,156,158Gd ^ i.QxiO" ). This behavior arises probably from the unstable configuration of the neutron deficit nuclei 152Gd -015 and r68Yb. This is not the case for the lightest 143 144 145 146 147 148 149 160 151 152 153 154 155 isotope of samarium 144Sm because the shape and Fig.l.Unit separation gains of Sm isotopes, sd is standard devia- charge distribution of this nucleus is stabilized by tion of the mean. the magic number of neutrons equal to 82. The values of separation gain of samarium count- References ed per unit mass difference is, in general, lower than Sm [1], Dembiriski W., Poniriski M., Fidler R.: Sep. Sci. Techn., those of ytterbium: eu.m. was found to be in the 33(11), 1693(1998). A Yb range (Z.2-h3.8)xlO while the values of eu.m. for [2]. Fiedler R., Donohue D., Grabmueller G., Kurosawa A.: Int. the six isotopes from 170Yb to 176Yb was found to be J. Mass Spectrom. Ion Processes, 122, 207-205 (1994). in the range (4.9^-6.6)xlO"4 [3]. The difference may [3]. Dembiriski W., Poniriski M., Fidler R.: INCT Annual Raport 1998. INCT, Warszawa 1999, pp. 70-71. be taken as evidence for a strong screening effect [4]. Fuji T., Yamamoto T., Inagawa J., Gunji K., Watanabe K., arising from 4f-orbital electrons of samarium. Pre- Nishisawa K.: Sol. Extr. Ion Exch., H, 1219-1229 (1999).