Abstract: A method of separating and concentrating the .sup.15 N isotope from natural abundance nitric oxide (NO) comprising mixing natural abundance nitric oxide in an appropriate mole ratio with carbon dioxide (CO.sub.2); irradiating the NO--CO.sub.2 mixture with coherent laser light of a desired wavelength, thereby selectively exciting the nitric oxide species containing the .sup.15 N isotope, which subsequently reacts with the carbon dioxide to form nitrogen dioxide (.sup.15 NO.sub.2); and separating said nitrogen dioxide (.sup.15 NO.sub.2) from the gas mixture.

Abstract: The invention involves the measurement of the concentration of the radioisotope .sup.129 I.sub.2 in the presence of a gas. The invention uses a laser to excite a sample of the .sup.129 I.sub.2 in a sample gas chamber and a reference sample of a known concentration of .sup.129 I.sub.2 in a reference gas chamber. The .sup.129 I.sub.2 in the sample and reference gas chamber each gives off fluorescence emissions which are received by photomultipliers which provide signals to a detector. The detector uses a ratioing technique to determine the concentration of .sup.129 I.sub.2 in the sample gas chamber.