A radiochemical neutron activation analysis for the determination of iodine in soil with the use of alkali fusion

A simple and rapid method has been developed for the determination of iodine in soil samples. Procedure: a 0.3g sample is weighed into a polyethylene bag, and irradiated for five minutes in the TRIGA II reactor of Rikkyo University. After cooling a few minutes, the sample is transferred to a 30ml nickle crusible. Iodine carrier solution containing a known amount of I-131 is added to the sample, which is then fused with a flux of 3g KOH and 1g KNO3. About 30ml of water is added in several portions to the crusible, and heated. Both the solution and the residue are transferred to a 100ml beaker. A few drops of sodiumhypochlorite solution is added. The content of the beaker is heated, and transferred to a 50ml centrifugal tube. The supernatant separated by centrifugation is transferred to another 100ml beaker. The solution is acidified with hydrochloric acid, heated, and cooled in a water bath. Sodium sulfite solution and palladium chloride solution are added, and the precipitate of palladium iodide is separated with a glassfiber filter paper. Gamma-rays from I-128 and I-131 in the precipitate are measured with a Ge(Li) detector coupled with a 4096 channel pulse height analyzer. Iodine contents of soils are calculated from the peak areas under the 443 keV gamma-ray of I-128. Corrections for chemical recovery are applied to them by means of the areas under the 365 keV gamma-ray of I-131. The present method was applied to a forest soil. The results were in good agreement with the results obtained by instrumental neutron activation analysis. The recovery of iodine in this procedure was about 80%. Decontamination factors for Mn and Na throughout the procedure were 4 x 104 and 1 x 104, respectivery. The time required for the chemical procedure was about an hour, when four samples were subjected to a parallel analysis. The limit of determination was 0.03μg iodine in a sample of 0.3g. (author)