SIMULTANEOUS RADIOCHEMICAL NEUTRON-ACTIVATION ANALYSIS OF IODINE, URANIUM AND MERCURY IN BIOLOGICAL AND ENVIRONMENTAL-SAMPLES

The determination of medium and long-lived nuclides can be combined wi th short-lived ones if a medium or long irradiation is made prior to t he short-irradiation and radiochemical processing. Thus, an RNAA metho d previously developed for determination of iodine based on the reacti on I-127(n,gamma)I-128(T-1/2 = 25 m) using oxygen flask ignition of th e irradiated sample,followed by solvent extraction with an iodine-iodi de redox cycle, was combined with an overnight preirradiation to induc e the U-235 fission product I-133 (T-1/2 = 20.8 h). By reactivating th e sample, cooled 1-2 days after the first irradiation, for few minutes both I-128 and I-133 could be quantified in the separated iodine frac tion. Non-combustible inorganic materials (e.g., sediment, soil, etc.) can be successfully ignited after mixing with excess cellulose powder . Chemical yields for iodine were determined spectrophotometrically in the organic phase, while homogeneously spiked Whatman cellulose powde r was used as uranium standard. Mercury is also released on ignition a nd collected in the absorbing solution, from where it was separated by toluene extraction. Its chemical yield was determined for each aliquo t using Hg-203 tracer and counting on an LEPD. Results for some suitab le SRMs are presented, and the general features of the double irradiat ion technique discussed.