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Radioactivity and Air Dose Rate


How have air dose rates decreased in forests?

The tendency of reductions in air dose rates has been investigated at many spots in forests. It was observed that air dose rates in forests have decreased basically following the half-life of radionuclides.

  • Air dose rates were measured in 2014 at the same spots in forests where the Forestry Agency took measurements just after the accident.
  • The air dose rates fluctuate depending on the kinds of tree. But on the whole, air dose rates in forests have decreased at the same rate as expected by radioactive decay alone.
  • Investigation on dynamics of cesium has revealed that most of cesium remains in forests and the amount of cesium migration to outside forests is small.
  • Fig.1 Air dose rates have been measured at many spots in forests in Fukushima Prefecture
    (cited from the Report on Investigation of Radiation Distribution)

  • Fig.2 Change of air dose rates in forests