A Gamma-ray camera to visualize 3-D distribution of radioactive 137-Cs sources

2016 Fiscal Year Final Research Report

• Project/Area Number: 15K12208
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Risk sciences of radiation and chemicals
• Research Institution: Waseda University
• Principal Investigator: Kataoka Jun 早稲田大学, 理工学術院, 教授 (90334507)
• Project Period (FY): 2015-04-01 – 2017-03-31
• Keywords: 土壌汚染 / 3D深度分布 / 散乱ガンマ線 / ガンマ線カメラ

Outline of Final Research Achievements

We developed a novel technique to visualize 3-D distribution of gamma-ray sources, particularly the distribution of 137-Cs which was released from the Fukushima daiichi plant in 2011. We showed that both (1) an event ratio between the full photo-absorption against Compton scattered events, and (2) image blurring due to scattering, can be an excellent estimator of the source localization in the soil, water and concrete. After detailed investigation based on the simulation and table-top experiments, we conducted number of field tests in the forest of Namie, Fukushima. We found that observed spectra can be well fit with a buffer depth beta=2.22+-0.05cm, where we assume distribution of 137-Cs follows as \propto exp(-z/beta). The results is consistent with independent measurements using a scraper prate, confirming the validity of our simple, but non-destructive measurement. We argue that similar approach can be also applicable in the SPECT in which scattered events are usually discarded.

Free Research Field

放射線イメージング