Isotope Enrichment Factors for Nitrogen-15 in the Nitric Oxide-Nitric Acid Exchange System

Single stage enrichment factors, α, for the isotope exchange reaction of nitrogen-15 between oxides of nitrogen and solutions of nitric acid have been determined by two different methods. Single stage equilibrations resulted in values of α that decrease from 1.065 for approximately 1M HNO3 to 1.045 for 11.1M HNO3. At high acid concentrations, α decreases rapidly owing to high concentrations of NO2 and N2O4 in the gas phase. Steady-state over-all separations in an exchange column at several rates of product with-drawal gave an independent determination for the 10M HNO3 used in the preparation of highly enriched nitrogen-15. Data from the two methods result in a value for α of 1.055±0.005 for approximately 10M HNO3 at 25°C.