Isotope fractionation due to sedimentation of atoms in centrifuged indium-lead alloy

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 × 10⁶ g for 100 hours at 150 °C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). ²⁰⁶Pb/²⁰⁸Pb and ²⁰⁷Pb/ ²⁰⁸Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy ²⁰⁸Pb isotope abundance increased and the light ²⁰⁶Pb isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of ²⁰⁶Pb/²⁰⁸Pb versus ²⁰⁷Pb/²⁰⁸Pb proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.