IMPROVED DETECTION LIMITS FOR TRACE-ELEMENTS ON AEROSOL FILTERS USINGCOMPTON SUPPRESSION COUNTING AND EPITHERMAL IRRADIATION TECHNIQUES

Aerosol samples were collected on Whatman 41 filters at two sites near Lake Huron and one site hear Lake Ontario. These samples were then an alyzed by instrumental neutron activation analysis (NAA) at the Univer sity of Illinois. The detection limits for certain trace elements were enhanced by irradiation with both thermal and epithermal neutrons and also by counting with Compton suppression techniques. The sample was divided in half to allow for four irradiations. Short-lived thermal NA A resulted in the determination of Al, Br, Ca, Cl, Cu, K, Mn, Na, Ti, and V. A short epithermal irradiation was used to determine Cu, I, In, Si, Sn, and U. A one and one-half hour epithermal irradiation was uti lized for the determination of As, Au, Br, Sm, Sb, and W. The elements Cr, Cs, Fe, Hf, Ni, Sc, Se, Th. Zn, and several rare earths were dete rmined with a long thermal irradiation. Utilizing a Compton suppressio n gamma-ray counting system reduced the background and enhanced the de tection of several isotopes which primarily emit only a single gamma-r ay upon decay. Counting was simultaneously performed with a normal cou nting mode so that the detection of isotopes with multiple decay gamma -rays was not impaired.