Analysis of I-129 in soil samples collected from Fukushima prefecture and estimation of their I-131/I-129 ratio

A large amount of ¹³¹I was released at the accident of Fukushima Daiichi Nuclear Power Plant occurred in March 2011. Because radioiodine accumulates in thyroid glands in human body, it is important to obtain data of ¹³¹I in the environment at the time of the accident. However, due to the short half-life of ¹³¹I has (8.02 days), it was not able to detect this nuclide after a few months. On the other hand, another iodine isotope, ¹²⁹I (half-life: 1.57 x 10⁷ y) released simultaneously with ¹³¹I, although the amount was very small. Because of its long half-life, ¹²⁹I should be detected in environmental samples such as soil in Fukushima Prefecture. Concentration of ¹²⁹I observed in soil samples showed a wide range, 5.3 x 10^-5 to 6.3 x 10^-2 Bq/kg. It is interested to note that a relatively good correlation was found between the concentrations of ¹³¹I and ¹²⁹I. This finding suggests the possibility to estimate ¹³¹I levels in soil samples through the analysis of ¹²⁹I. In addition to we measured depth distribution of ¹²⁹I, but this is being measured. (author)