The Self-Diffusion Coefficient of Uranium Hexafluoride

A method is reported for measuring the self-diffusion coefficient of a vapor by observing with a mass spectrometer the rate at which material enriched in one isotope diffuses into normal material in an apparatus of known geometry. A value of $\rho D$ (where $\rho$ is the density and $D$ the diffusion constant) was obtained for uranium hexafluoride at 30°C. Knowledge of the viscosity together with the constants reported here allow calculation of the molecular force law.