First application to environmental gamma-ray imaging with an electron tracking compton camera

An electron tracking Compton camera (ETCC) has been developed for the application of an image mapping of gamma ray from cesium in environment for the purpose of decontamination work in Fukushima. A first prototype ETCC was built based on established technologies in the MeV/sub-MeV gamma cosmic-ray search in astronomy. After the performance test using a ¹³⁷Cs radiation source, the field test was performed at Shirakawa, Fukushima. In this test, fine images of contaminated soil bags were obtained with ETCC. By comparing energy spectra with a background spectrum, we can naively estimate radiation doses from each test sample. These results suggest that we can succeed in imaging of gamma ray from low contaminated soils around 0.02 μSv/hr, even if the radiation dose is lower than a background ambient dose of approximately 0.05 μSv/hr. After improving ETCC detection efficiency and developing associated software and hardware systems, we expect the ETCC yields to an imaging and dose monitor device to measure contaminated soils in less than 15 min in a radiation dose of approximately 0.2 μSv/hr in environment.