Joint Environmental Radiation Survey by JAEA and KAERI Around the Fukushima Daiichi Nuclear Power Plant: Performance of Mobile Gamma-Ray Spectrometry Using Backpack and Carborne Survey Platforms

According to the implementing arrangement between the Japan Atomic Energy Agency (JAEA) and the Korea Atomic Energy Research Institute (KAERI) in the field of radiation protection and environmental radiation monitoring, a joint survey program was performed to assess ground deposition of radioactive cesium in areas surrounding the Fukushima Daiichi Nuclear Power Plants. The purpose of this joint survey was to evaluate the field applications of the developed survey systems and methodologies. Understanding the performance of each system within a cesium-deposited contaminated zone is important for ensuring an appropriate response following a nuclear accident. The results of the measured ambient dose rates determined using each survey method were compared. Two kinds of survey system were used in the mobile gamma-ray spectrometry, which were MARK-M1 (Monitoring of Ambient Radiation of KAERI-the 1st Multipurpose system) based on two LaBr3(Ce) detectors of KAERI and KURAMA-II (Kyoto University Radiation Mapping - II) system with one CsI(Tl) detector of JAEA. First, mobile gamma-ray spectrometry using a backpack survey platform was conducted to assess the distribution of dose rates around specific survey sites, which were expected to be slightly contaminated by radioactive cesium in Minamisoma and Tomioka. A carborne survey using two gamma-ray spectrometers loaded inside a vehicle was successfully conducted to compare the measured dose rates in routes from site to site and verify evaluation methods, including attenuation correction.