抄録
A theoretical calculation is made of the back-diffusion coefficient, b, of diffusion pump, giving the formula:
b=exp(-4[ƒ(+)-ƒ(-)]qL/λON_??_),
where ƒ(+)-ƒ(-) represents the fraction of gas molecules travelling towards the fore vacuum side after the collisions with pumping fluid molecules, q the rate of flow of the fluid vapor stream, L the effective length of the stream, N the molecular density at 1μHg pressure, λ0 the mean free path of a fluid molecule in the gas at N concentration and v the mean molecular velocity of gas. This formula explains satisfactorily Dayton's experiments with octoil and air. The difference from the earlier theories lies in the free-molecule treatment of the pumping action whereby thorough consideration is given to the mechanism of intermolecular collisions.
