A concentration of nitrogenhyphen;15 has been effected in a thermal diffusion column under conditions where the gaseous exchange action, N14O2+N15Orlarr2;N15O2+N14O, can contribute to the separative process. The top of the column is fed with NO2of normal isotopic abundance. Reversible thermal decomposition of NO2into NO and O2establishes a radial concentration gradient so that the descending cold stream is predominantly NO2and the inner hot ascending stream is largely NO and O2. As a result of the exchange reaction, N15preferentially concentrates in the NO2and is carried to the bottom of the column. Here the enriched NO2rehyphen;enters the hot rising stream and is again decomposed into NO which undergoes further exchange. This reversible thermal decomposition makes it possible to operate the column without a chemical converter as was needed in the COsngbnd;CO2system.The overhyphen;all isotope separation has been studied in a twohyphen;meter column as a function of pressure (0.25 to 1.0 atmosphere), temperature (400 to 700deg;C) and withdrawal rate (5 to 66 cc atmospheres per day). A maximum overhyphen;all separation of 2.6 was obtained at a filament temperature of 685deg;C and a pressure of 0.5 atmosphere. At a withdrawal rate of 27 cc atmospheres the overhyphen;all separation is about 70 percent of this maximum value.The system is a rather complicated one, and it is not yet possible to completely evaluate the contribution of each separative process that can occur in the column.
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