NUCLEAR SIZE AND SHAPE EFFECT IN CHEMICAL ISOTOPE EFFECT OF GADOLINIUM USING DICYCLOHEXANO-18-CROWN-6

ABSTRACT

Gadolinium isotopes were fractionated in a liquid-liquid extraction system using dicyclohexano-18-crown-6. The isotope enrichment factors showed breakdowns of the conventional Bigeleisen-Mayer approximation for every condition of the initial phases; the concentrations of gadolinium and hydrochloric acid and the type of organic solvents. The nuclear mass effect and the field shift effect were estimated by use of the isotope pairs ¹⁵²Gd-¹⁶⁰Gd and ¹⁵⁴Gd-¹⁶⁰Gd. Since both isotopes, ¹⁵²Gd and ¹⁵⁴Gd, have the unique characteristics of the nuclear charge radii, <r²>'s, the unusual isotope effects due to the field shifts took place, while the mass effects of the other isotopes canceled the field shift effects. The maximum isotope effect was observed to be ε_160,152 =0·0252 ± 0·0024 whose initial aqueous phase was 0·023 M GdCl₃ in 12 M HC1, and its organic phase was 0·2 M DC18C6 in chloroform: this was 0·00315 ± 0·00030 in terms of the enrichment factor for unit mass.