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. These simple activation methods are quite sensitive, nondestructive, and require only a short amount of beam time (one minute in most cases) for each sample analysis. The method for determination of nitrogen in aerosols uses a proton beam to induce the /sup 14/N(p,..cap alpha..)/sup 11/C reaction. The detection system consists of a Ge(Li) gamma-ray spectrometer. A comparison 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 ..mu..g/cm/sup 2/. The method for determination of carbon in aerosols uses a deuteron beam to induce the /sup 12/C(d,n)/sup 13/N reaction. 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 ..mu..g/cm/sup 2/. Two methods were developed for determination of oxygen in atmospheric aerosols. One method uses a /sup 3/He beam to induce the /sup 16/O(/sup 3/He,p)/sup 18/F reaction. The second method uses a proton beam to induce the /sup 16/O(p,..cap alpha..)/sup 13/N reacton. The two methods were used to check one another. A comparison of the oxygen found in ten samples by /sup 3/He 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 ..mu..g/cm/sup 2/ and is primarily limited by the rather large oxygen blank in the silver filter

A method for replicating ice accretion roughness using multi-scale analog distributions.

A new approach of creating an analog surface for a surface with natural roughness is presented based on the hypothesis that the dominant skin friction and heat transfer augmentation mechanisms are 1) the vortex shedding from the roughness elements and 2) the interaction of the shed vortices with the next downstream roughness elements. An autocorrelation function was employed on a real ice surface to capture the root-mean-square-roughness height, the primary streamwise wavelength, and the aspect ratio of surface microscales. Two distributions of deterministic roughness, one of ellipsoids and one of elliptical cones, were created to match the primary features of the real ice surface. This work describes the analog surface creation method and characterizes the convective enhancement and velocity boundary layer development of the analog surfaces. The convective enhancement and velocity boundary layer results associated with the analog surfaces are then compared to those of the real ice surface

DETERMINATION OF CARBON IN ATMOSPHERIC AEROSOLS BY DEUTERON-INDUCED NUCLEAR REACTIONS

Nuclear reactions induced by 7.6-MeV deuterons are used to determine total carbon in atmospheric aerosols. The {sup 12}C(d,n){sup 13}N reaction produces the radionuclide {sup 13}N, a 10.0-min positron emitter, which is detected by its 0.511-MeV annihilation radiation. The detection system is a Ge(Li) {gamma}-ray spectrometer. The method is nondestructive of the sample, permitting the sample to be studied by additional methods. Comparison of carbon found by deuteron activation analysis with that found by independent but destructive combustion methods shows a standard deviation of 10% for 15 samples analyzed over a wide range of carbon contents. The detection limit is estimated to be 0.5 {micro}g/cm{sup 2}, corresponding to a carbon concentration of 0.2% in a sample of total thickness 250 {micro}g/cm{sup 2}

Determination of nitrogen in atmospheric aerosols by proton activation analysis

Nuclear reactions induced by 7.6-MeV deuterons are used to determine total carbon in atmospheric aerosols. The {sup 12}C(d,n){sup 13}N reaction produces the radionuclide {sup 13}N, a 10.0-min positron emitter, which is detected by its 0.511-MeV annihilation radiation. The detection system is a Ge(Li) {gamma}-ray spectrometer. The method is nondestructive of the sample, permitting the sample to be studied by additional methods. Comparison of carbon found by deuteron activation analysis with that found by independent but destructive combustion methods shows a standard deviation of 10% for 15 samples analyzed over a wide range of carbon contents. The detection limit is estimated to be 0.5 {micro}g/cm{sup 2}, corresponding to a carbon concentration of 0.2% in a sample of total thickness 250 {micro}g/cm{sup 2}