GENERAL OUTLINE. THERMAL DIFFUSION

The discovery in 1938 of a separation column procedure has permitted preparation in the pure state of different isotopes and created, in a general fashion, a renewal of interest in gas kinetics. Recent developments indicate the mastery attained in the separation of isotopic mixtures with multiple constituents. These works have led to the establishment of a scheme of theoretical relations which permit the advance calculation of the quasi- stationary distribution of different isotopes of isotopic molecules. The practical application possibilities were examined in the case of oxygen and confirmed. The method of auxiliary gas addition has shown itself to have satisfactory utilization by giving the possibility of producing rare isotopes in extremely pure state, such as Ar/sup 38/ and Ne/sup 21/. Moreover, this system will be very useful in the preparation of O/sup 17/ and S/sup 34/. One relatively new fact is the knowledge of the effect of the moment of inertia on the thermal diffusion as it was shown for systems of Ar/sup 40/ with the four hydrochloric gases and of Ne or Ne/sup 22/ with the different methanes. The separation column has found special applications, for example, in the determination of the archeological age by the C/sup 14/more » method using Ar/sup 38/. Finally, the new definition of the meter is based on the possibility of preparing in the pure state the isotope K/sup 86/ in the separation column and of measuring in vacuum the wavelength of its orange ray 5d/sub 5/-- 2p/sub 10/ with a precision of 1: 10/sup 9/. (tr-auth)« less