Methodology for iodine-129 determination in coniferous plant by neutron activation

Full text: The measurement methods of iodine-129 (129I) include liquid scintillation counting, mass spectrometry analysis, X-ray spectrometry and neutron activation analysis. The combination of long half-life and low radiation energy, limit the sensitivity of a direct measurement in environmental matrixes. The neutron activation analysis (NAA) permits the increase in the sensitivity because of the high thermal neutron cross section of 129I. The reaction produced is 129I (n,γ) 130I and the Eγ (536 keV) of iodine-130 (t1/2 = 12,6 hours) is measured. The developed methodology allows the determination of 129I in coniferous needles using NAA. The chemical treatment removes the interferences present in the matrix, as well as the Bromine-82 originated in the activation process. The analytical method is divided in six steps: a) digestion by alkaline fusion; b) radiochemical purification of 129I by distillation followed by solvent extraction; c) distillation and adsorption on activated charcoal; d) neutron irradiation; e) radiochemical purification of 130I by distillation followed by solvent extraction; f) gamma spectrometry. Iodine-131 tracer is added, and a chemical recovery of 95% in the distillations is obtained. The whole process recovery is within 70% and 85%. The detection limit is 0.48 mBq. Several factors affect this value, such as sample type, variety of coniferous, natural iodine concentration, irradiation time and neutron flux. (author)