The determination of the quantum mechanical diffraction effects on thermal diffusion

FOM. Laboratorium voor Massascheiding, Kruislaan 407, Amsterdam. O. Netherlands, Netherlands.

Abstract

In order to investigate the influence of diffraction effects on the thermal diffusion factor at low temperatures a two bulb apparatus was used, of which the upper reservoir was maintained at a constant temperature, the room temperature Th, while the temperature of the lower reservoir was varied from room temperature down till 12 °K.

The mixtures used were helium with tracer amounts of the tritium compounds T₂, DT and HT, and H₂ with tracer amounts of HT.

The measurements show a very big influence of the diffraction effects on the thermal diffusion factor, especially at those temperatures where the De Broglie wavelength of the particles becomes of the same order as the diameter. There is a very pronounced difference between the thermal diffusion factor α_T2-He, where both particles may be assumed to be spherically symmetric and the thermal diffusion factors of the other mixtures, where the symmetry is disturbed by the mass distribution in the molecule. A comparison with theory could not be made, because up till now no calculations are available for the quantum parameters of the mixtures we used. Moreover, all calculations that are available, are concerned with spherical symmetric molecules.