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. 2011:1:87.
doi: 10.1038/srep00087. Epub 2011 Sep 7.

The time variation of dose rate artificially increased by the Fukushima nuclear crisis

Masahiro Hosoda  1 , Shinji Tokonami, Atsuyuki Sorimachi, Satoru Monzen, Minoru Osanai, Masatoshi Yamada, Ikuo Kashiwakura, Suminori Akiba
Affiliations

The time variation of dose rate artificially increased by the Fukushima nuclear crisis

Masahiro Hosoda et al. Sci Rep. 2011.

Abstract

A car-borne survey for dose rate in air was carried out in March and April 2011 along an expressway passing northwest of the Fukushima Dai-ichi Nuclear Power Station which released radionuclides starting after the Great East Japan Earthquake on March 11, 2011, and in an area closer to the Fukushima NPS which is known to have been strongly affected. Dose rates along the expressway, i.e. relatively far from the power station were higher after than before March 11, in some places by several orders of magnitude, implying that there were some additional releases from Fukushima NPS. The maximum dose rate in air within the high level contamination area was 36 μGy h⁻¹, and the estimated maximum cumulative external dose for evacuees who came from Namie Town to evacuation sites (e.g. Fukushima, Koriyama and Nihonmatsu Cities) was 68 mSv. The evacuation is justified from the viewpoint of radiation protection.

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Figures

Figure 1
Figure 1. (a) Expressway survey route for measuring dose rates in air from Hirosaki City to Fukushima City.
The starting point on March 16 and April 11 was Hirosaki City and on April 25 it was Fukushima City. Total distance on the expressway was 1256 km. (b) Temporal variation of dose rates in air before and after the start of the Fukushima NPS crisis. The black line shows the dose rate in air reported by Minato in 2006. The solid black symbols are dose rates in air measured on August 2, 2010. The red, green and blue lines are dose rates in air measured on March 16, April 11 and April 25, 2011, respectively.
Figure 2
Figure 2. Comparison of measured dose rates in air on pavement and uncovered surfaces.
Figure 3
Figure 3. (a) Survey route for measuring dose rates in air within the high level contamination area.
Total distance for the car-borne survey in this area was 730 km. (b) Distribution map of the dose rates in air within the high level contamination area in Fukushima Prefecture. The rates were classified into eleven groups from <2 μGy h−1 to >20 μGy h−1 at intervals of 2 μGy h−1.
Figure 4
Figure 4. Temporal variation of in-situ gamma spectra measured at Kunimi, Fukushima Prefecture (a) and Oshu, Iwate Prefecture (b).
See this image and copyright information in PMC

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