SEPARATION OF STRONTIUM AND BARIUM ISOTOPES USING A CROWN-ETHER - DIFFERENT BEHAVIORS OF ODD-MASS AND EVEN MASS ISOTOPES

Isotope effects were investigated for strontium and barium complexes of dicyclohexano-18-crown-6. The isotopes of odd mass number behaved differently than those of even mass number. A value of epsilon(O/E), which represents the difference between the isotope of odd mass number a;ld that of even mass number, was -0.0017 for Sr-87, -0.011 for Ba-135, and -0.009 for Ba-137. The unit mass enrichment factors were epsilon(u) = -0.0009 for strontium and epsilon(u) = 0.004 for barium. The direction of enrichment was opposite for strontium and barium, and the absolute value of the enrichment factor of barium was larger than that of strontium isotopes. This phenomenon was attributed to the difference in the predominant form of the strontium and barium ions in the aqueous solution. That is, the population of aquo-complexes is larger than that of anionic complexes for strontium, while the reverse is the case for barium.