Determination of low-z elements in atmospheric aerosols by charged-particle-induced nuclear reactions

Nuclear reactions induced by charged particles are used to determine total carbon, nitrogen, and oxygen in atmospheric aerosols. The method for determination of nitrogen in aerosols uses a proton beam to induce the 14N(p,α)11C reaction. Radioactive 11C, a 20.4-min positron emitter, is detected via its 0.511-MeV annihilation radiation. The detection system consists of a Ge(Li) gamma-ray spectrometer. A comparision of nitrogen found by the proton activation method with that found by an independent but destructive combustion method gave an average percent difference of 14% for 17 samples analyzed over a concentration range that spans two orders of magnitude. The sensitivity for detection of nitrogen is approximately 0.1 μg/cm2. The method for determination of carbon in aerosols uses a deuteron beam to induce the 12C(d,n)13N reaction. The 10.0-min 13N was followed by its 0.511 MeV annihilation radiation. The results of the deuteron activation analysis of 15 samples were compared to the results of an independent combustion method. The comparison shows an average percent difference of 10%. The sensitivity for detection of carbon is approximately 0.5 μg/cm2. Two methods were developed for determination of oxygen in atmospheric aerosols. One method uses a 3He beam to induce the 16O(3He,p)18F reaction. The 109.8-min 18F was followed by its 0.511 MeV annihilation radiation. The second method uses a proton beam to induce the 16O(p,α)13N reaction. The two methods were used to check one another. A comparison of the oxygen found in ten samples by 3He activation analysis with that found by proton activation analysis shows an average percent difference of 18%. The sensitivity for detection of oxygen is approximately 5 μg/cm2 and is primarily limited by the rather large oxygen blank in the silver filter