Determination of some elements by epithermal neutron activation analysis for the Arctic aerosol

We determined nineteen trace elements in 685 aerosol filter samples collected during 1964-1978 in northern Finland by the Finnish Meteorological Institute. In this paper we present some procedures and results for very short (similar to 25 s), short (similar to 3-54 min), and medium (12-35 h) lived isotopes as determined by epithermal NAA in conjunction with and without Compton suppression. Elements with a I-gamma/sigma(th) ratio are favorable to be determined by epithermal NAA. Silver was determined by a one minute epithermal irradiation because of a very short Ag-110 half-life. Antimony, arsenic, cobalt, bromine, indium, iodine, potassium, silicon, tin, tungste, and zinc were determined by a ten minute epithermal irradiation. For silver determination, samples were counted without transferring the filter from the irradiated vial, however, for ten minute irradiation all samples were transferred to a non-irradiated vial and counted both in the normal and Compton mode by the HPGe gamma-spectrometry system with a decay time of about 10 minutes and counting time of 15 minutes. Each day a miximum of 16 samples were irradiated and immediately following the short counting, these samples were loaded into an automatic sample changer in sequence of irradiation and counted for an hour in both normal and Compton modes. This has proven to be an extremely cost effective measure thus reducing the need to employ long-lived NAA to analyze other elements such as Ag, Co, Sn and Zn and Ag for air pollution source receptor modeling.