A SCREENING SURVEY EXERCISE FOR THYROID INTERNAL EXPOSURE FROM RADIOIODINE AFTER A NUCLEAR ACCIDENT

In the aftermath of the 2011 Fukushima nuclear disaster, a screening survey for thyroid internal exposure from intake of radioiodine was performed on 1080 children using handheld NaI(Tl) survey meters. This article presents the design and results of a practical exercise conducted to develop the skills of personnel who would be potentially engaged in such a survey. Participants of this exercise were asked to measure manikin heads in which point sources were installed under normal (~0.05 μSv h-1) and elevated (~0.5 μSv h-1) background conditions. The results demonstrated that the measurements were less dependent on the background radiation level, and the deviation of net signals obtained by the participants were within 10-20% for dose rates above 0.2 μSv h-1. This result suggests that dose rates can be reliably obtained above a provisional operational intervention level for the device, 0.5 μSv h-1 under a real nuclear accident situation.