Kc.t' Word Jndex-Trace metals; neutron activation analysis; preconcentrution,A prcconccntration method incorporated with neutron activation analysis was . developed for the accurate determination of trace metals in biological and environmental samples. Bismuth dicthyldithiocarbamatc, thallium 'diethyldithiocarbamate.arid ammonium pyrrolidinedithiocarbamatc were used as the prcconcentraticn agents for three groups of metals. Trace metals were enriched and interfering elements such as Na, Br, P. K. etc. were-removed simultaneously during the preconcentration process so that 'the sensitivity for each metal was greatly improved. Optimal conditions for sample digestion, group preconcentratlon of trace metals and neutron activation analysis of biological and environmental samples were discussed.

Synopsis We report the investigation on three-body fragmentation of CF4 3+ induced by 1 keV electron collision utilizing an ion momentum spectrometer. With the help of coincidence measurement for three fragment ions, the channel CF4 3+→F++CF2++F+ is identified. By employing Dalitz plot and Newton diagram, a sequential path-way and a concerted pathway are uncovered, which are further separated by momentum correlation of two F+ ions. We find that the CF4 3+ fragmentation prefers a sequential pathway CF4 3+→F++CF3 2+→F++ F++CF2 +.