Neutron Activation Analysis of F, Sc, Se, Ag and Hf in Aerosols Using Short-lived Isotopes

Abstract

An 18-sec neutron irradiation of fluorine, scandium selenium and silver produces the following short-lived isotopes:²⁰F (11.1 S),^46mSC(18.7 s), ^77mSe (17.7 s), ^ll0Ag(24.6 s) and ^179mHf (18.7 s). A 20-sec Ge(Li) count after a 10-sec decay period allows the simultaneous detection of these five isotopes in aerosols. Errors due to fast decay during the counting are minimized by the use of a dead-time stabilizer. The high initial counting rates due to energetic beta rays of short-lived isotopes are reduced by the use of absorbers. Fluorine is also determined, using the threshold reaction ¹⁹F(n, p) ¹⁹O(26.9 s). The interference due to (N, γ) reactions on other impurities in the collected aerosol is reduced by a 30-sec irradiation under cadmiumaover, and a 30-sec count after a 25-scc decay period. The activation of silver and hafnium is enhanced also by an irradiation under cadmium owing to their important resonance peaks. The technique is applied to the analysis of aerosols sampled in Belgium, at urban, industrial and background stations.