Symmetry Effects in Gas Kinetics. I. The Helium Isotopes

Continuing earlier investigations, we discuss in this paper the influence of the process of symmetrization of the wave functions of the colliding atoms upon various gas-kinetic cross sections. Through the choice of a suitable interaction potential it thus becomes possible to derive the temperature dependence of the viscosities of the two He isotopes near absolute zero; it is also possible to show that the differences between these two quantities is largely caused by the fact that the nuclei of ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ follow different statistics. The agreement between theory and experiment is not quite as satisfactory in the case of the viscosity of mixtures of the two isotopes. Finally, curves are presented showing the effect of symmetrization on various possible scattering experiments.