The Distribution Map of Radiation Dose, etc., has been created on the basis of the results of a variety of monitoring activities conducted by the MEXT to give public access to the details of the influence of radioactive substances discharged from TEPCO Fukushima Daiichi Nuclear Power Plant.

MEXT Extension Site of Distribution Map of Radiation Dose, etc. Digital Japan Web System

About the Establishment of the Extension Site of Distribution Map of Radiation Dose, etc.

1. Background and purpose

This Extension Site of the Distribution Map for Radiation Dose (hereafter “this site”) was prepared in the course of the 2011 Strategic Funds for the Promotion of Science and Technology and entitled “Establishment of the Base for Taking Measures for Environmental Impact of Radioactive Substances—Study of the Distribution of Radioactive Substances”; the 2011 Radioactivity Measurement and Investigation Project commissioned by MEXT entitled “Investigation and Study of the Secondary Distribution of Radioactive Substances due to the Accident at the Fukushima Daiichi Nuclear Power Plant”; and the 2011 Radioactivity Measurement and Investigation Project entitled “Establishment of Technique for Identifying Long-term Impact of Radioactive Substances due to the Accident at the Fukushima Daiichi Nuclear Power Plant based on the Distribution Map of Radiation Dose, etc., the Vehicle-Borne Survey Map, and the results of airborne monitoring projects under the MEXT in order to observe in detail the impacts of radioactive substances discharged from the TEPCO Fukushima Daiichi Nuclear Power Plant.

1. Distribution Map of Radiation Dose, etc.
Air dose rate measurements are taken at one location per 2 × 2 km mesh in the 80 km radius area from TEPCO Fukushima Daiichi Nuclear Power Plant and at one location per 10 × 10 km mesh in the 80 to 100 km radius area and other parts of Fukushima Prefecture outside these areas. Additionally, nuclide analyses are conducted of 5 cm surface soil samples taken from up to five spots per location. The Distribution Map of Radiation Dose, etc., shows the results of the measurements and analyses to enable continuous monitoring of the impact of radioactive substances deposited on the ground surface on resident's health and the environment in future years.
2. Distribution Map of Radiation Dose, etc. (Vehicle-Borne Survey Map)
The Vehicle-Borne Survey Map shows the results of continuous air dose rate monitoring, which are obtained by vehicle-borne surveys* conducted mainly along national and prefectural roads within an approx. 100 km radius area from TEPCO Fukushima Daiichi Nuclear Power Plant to observe in detail the influences of radioactive substances on roadside areas.
*A vehicle-borne survey is a technique in which radiation detectors are installed on vehicles, and gamma rays from radioactive substances deposited on the ground are measured quickly, and in detail, in order to continuously measure air dose rates around roadside areas. In this monitoring survey, the KURAMA system, which was originally developed by Kyoto University, was used with the cooperation of Fukushima Prefecture.
3. Airborne Monitoring Map
The airborne monitoring map is based on the results of airborne monitoring* and the like conducted since April 6, 2011, by the MEXT with cooperation of the US Department of Energy, etc., and shows the air dose rate 1 m above the ground surface and the ground surface deposition densities of radioactive substances at each reading point. This map provides the outline of the influences of radioactive substances deposited on the ground surface.
*Airborne monitoring is a technique in which highly sensitive, large radiation detectors are installed on aircraft, and gamma rays from radioactive substances deposited on the ground are quickly measured over a large area in order to check surface deposition.

The overall map will continue to be updated with additional area maps created based on the originally collected data, and the map based on chronologically newer data will hereafter be published on this site.

Before using this site, carefully read and fully understand the guide to this site and the intent of the information provided in it and agree and consent to the terms and conditions of use.

2. User's Agreement and Terms and Conditions of Use
  • This Agreement provides for the terms and conditions under which the Extension Site of the Distribution Map of Radiation Dose, etc., can be used. In this Agreement, a "User" means a person that uses this site and a "map" refers to cartographic information generated, using Digital Japan geographic information or software (hereafter "geographic information, etc.") via this site, from monitoring-related data measured or published by the MEXT.
  • The maps available on this site use the Digital Japan Web System to provide information on the influences of radioactive substances discharged from TEPCO Fukushima Daiichi Nuclear Power Plant and deposited on the ground surface. The User shall use these maps in accordance with the "Digital Japan" Common User's Agreement.
  • The User of this site shall not violate or infringe the property rights and related rights, including personal rights, of the above-mentioned copyright and related rights holders.
  • The User shall be aware that no information available from this site can be used for profit.
  • No map available on this site shall be quoted in any other documents without explicitly referring to the "Extension Site of Distribution Map of Radiation Dose, etc.,/Digital Japan" as the source of the map.
  • The User shall follow the Rules And Manners for Internet Users (Internet Association Japan: http://www.iajapan.org/rule/). The User shall be strictly prohibited from disseminating the types of information that may be deemed as antisocial or illegal in light of the above Rules and Manners.
  • The User shall be solely and entirely responsible for any direct or indirect damage arising from the use of this site; and this site shall not be held responsible or liable in any way for any such damage. The User shall use this site at their own risk and discretion.
  • Upon using this site, the User shall be deemed to have accepted the terms and conditions of this Agreement.
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4. Other remarks
  • Note that the maps available on this site include errors that may occur during the creation of monitoring-related data or cartographic information. These maps are intended for use as reference information.
  • Additionally, monitoring-related data are created using the methods described below. Therefore, measurement values contain some degrees of errors. It should also be noted that various cartographic information may exist and be intermixed on different scale levels (positional accuracy levels).
    1. Distribution Map of Radiation Dose, etc.:The hourly air dose rate (μSv/hour) 1 m above the ground surface at each reading point is determined as follows: individual reading points are identified using commercially available GPS devices; then, at each location with an air dose rate of 30 μSv per hour or less, measurements are taken using a calibrated NaI(Tl) scintillation survey meter; and measurements are taken using a calibrated ion chamber survey meter at each location with an air dose rate exceeding 30 μSv per hour.
      Soil samples taken from up to five spots in each reading point are agitated in suspension for nuclide analysis using a calibrated Ge semiconductor detector. The averaged results of the nuclide analysis provide the basis for the surface deposition densities of iodine-131 and cesium-134 and 137 per unit area (Bq/m2) at each reading point.
    2. Distribution Map of Radiation Dose, etc. (Vehicle-Borne Survey Map):The KURAMA System (Kyoto Univ. RAdiation MApping System) connected to on-vehicle NaI(Tl) scintillation survey meters is used to determine the hourly air dose rate (μSv/hour) 1 m above the road surface (as measured aboard). The values shown on the map as air dose rates measured by the on-vehicle survey meters are determined by factoring in the shielding effect of the construction of the monitoring cars, the installation height of the survey meters, and by multiplication with the correction coefficient for the air dose rates measured inside and outside the cars.
    3. Airborne monitoring map:Using high-sensitivity radiation detectors installed on helicopters, second-by-second measurements are taken of the gamma rays emitted from radioactive substances deposited in circles of a diameter approximately twice the flight altitude (target altitude: 150 to 300 m) centering around ground locations right below the flight trajectories. Then, a dedicated software program is used to determine the hourly air dose rate (μSv/hour) 1 m above the ground surface at each location based on the value of gamma rays measured up in the air and the reading of the survey meter on the ground.
      Meanwhile, the deposition density of radioactive cesium per unit area of ground surface (Bq/m2) is determined, using another dedicated software program, from the relationship between the results of ground surface measurement by a Ge semiconductor detector and the air dose rate 1 m above the ground surface. Note that values for points not flown (i.e., points not present on the flight trajectories) are determined by interpolation from measurement values obtained from points flown.
  • The User's Agreement, etc., (functions, content, terms and conditions, explanations, and all other information) of this site may be subject to change or removal without prior notice. It should also be noted that access to or use of this site may be interrupted from time to time as the result of an update of its content, maintenance and other tasks, or a power failure.
  • If a problem occurs such as "no map appears" or "an error has occurred," consult the Q&A page of Japan Digital Web System.
  • If this site is likely to be down due to excessive access requests, priority shall be given to municipal and government officials. For users who are denied access, enlarged versions of maps shall be made available in PDF format (Portable Document Format).