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 with short-lived ones if a medium or long irradiation is made prior to the short-irradiation and radiochemical processing. Thus, an RNAA method previously developed for determination of iodine based on the reaction I-127(n,gamma)I-128(T-1/2 = 25 m) using oxygen flask ignition of the irradiated sample,followed by solvent extraction with an iodine-iodide redox cycle, was combined with an overnight preirradiation to induce the U-235 fission product I-133 (T-1/2 = 20.8 h). By reactivating the 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 fraction. 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 powder was used as uranium standard. Mercury is also released on ignition and collected in the absorbing solution, from where it was separated by toluene extraction. Its chemical yield was determined for each aliquot using Hg-203 tracer and counting on an LEPD. Results for some suitable SRMs are presented, and the general features of the double irradiation technique discussed.