Theory of Degenerate Non-Ideal Gases

The partition function for a non-ideal quantum gas is calculated by considering the degeneracy exactly and the inter-particle forces only so far as binary collisions are concerned. In the absence of forces, this reduces to the ideal Einstein-Bose or Fermi-Dirac gas, as the case may be, rather than to the ideal classical gas. If the wave functions describing the two-particle collision are known, the partition function can be reduced to a set of quadratures. The theory is applied to the phase transition in liquid helium in the following paper, and other possible applications are discussed here.