The reason why air dose rates in houses are lower than those outside

Fig.1　Depandence of air dose rates on the position
(Result from simulation)

• The reason why air dose rates in houses are in general lower is that there is no cesium deposits under the house.
• If there is no radiation source within 5 m from the center, the air dose rate at the center position is about half of that of outside.
• Air dose rate at the border of a house suddenly changes.So air dose rates at the border should be carefully measured.

Conversion coefficients in Fukushima

Fig.2　Result for conversion coefficient measured in general houses in Fukushima Prefecture

• Conversion coefficient for reducing radiation at the first floor of a house is about 0.4 on average. But the value changes depending on individual houses.
• In the places where air dose rates are low, the effect of natural radiation from ground should be separately considered.
• We should be careful to measure air dose rates around houses because they change considerably.

(Report on Investigation of Radiation Distribution: http://fukushima.jaea.go.jp/initiatives/cat03/entry06.html)

Conversion coefficient changes depending on the size and shape of a house.

Related articles

• In what ways does exposure to radiation occur the environment? What kinds of radiation exposures are important in Fukushima?
• Does the radiation dose measured with a personal dosimeter represent the real radiation dose?
• What kinds of measurements and evaluations for radiation doses have been conducted until now? What are the results?

Reference

1. Matsuda, N. et al, Depth profiles of radioactive cesium in soil using a scraper plate over a wide area surrounding the Fukushima Dai-ichi Nuclear Power Plant, Japan, Journal of Environmental Radioactivity, vol.139, 2015, p.427-434.