Temperature Dependence of Isotope Effects of Barium Using a Crown Ether

Barium isotopes were fractionated in a liquid-liquid extraction system using a crown ether of dicyclohexano-18- crown-6. The temperature dependence of isotope enrichment factors was investigated at 273.2 to 323.2K. Within the experimental error, the isotope effects appeared to be ruled by the conventional mass-dependent theory. The maximum isotope effect was observed at 323.2K, whose isotope enrichment factor for unit mass difference was ε_u=-0.00044±0.00013. Relation between ε _u and 1/T showed a characteristic curve, but was deviated from a temperature-dependent theory of ε a/T+b/T ². The change in the coefficient a in the present system was discussed by considering the obtained results.