Neutron Activation Analysis of ¹²⁷I and ¹²⁹I in Environmental Samples

Abstract

The analytical method of ¹²⁷I and ¹²⁹I in environmental samples has been studied and the background levels of these nuclides in soils, seaweeds and milk were measured.
The analytical method consists of the combustion technique and neutron activation analysis (N. A. A.).
The iodine was separated from samples by ignition at about 1, 000°C in a quartz combustion apparatus with an oxygen and a nitrogen stream, and was absorbed by small amounts of active charcoal. The iodine was then purified through the carbontetrachloride extraction method and the PdI₂ decomposition method. Irradiation was conducted by JRR-4 (n_th: 8×10¹³n/cm²·sec) for 40min. After irradiation, the iodine was purified by the solvent extraction method same as pre-irradiation extraction. Each activity of ¹²⁶I and ¹³⁰I, which was produced by ¹²⁷I (n, 2n) ¹²⁶I and ¹²⁹I (n, γ) ¹³⁰I reaction respectively, was measured by γ-spectrometry using a Ge-detector.
The lower detection limits of ¹²⁹I by this method were 4×10^-7Bq/g for dry soil, 7×10^-8Bq/g for fresh seaweeds and 7×10^-6Bq/l for fresh milk, respectively. The relative standard deviation of ¹²⁹I measurements in soil and milk were less than 10%.