Abstract
A car-borne survey was carried out in the northwestern, or Tokatsu, area of Chiba Prefecture, Japan, to make a detailed distribution map of absorbed dose rate in air four years after the Fukushima Daiichi Nuclear Power Plant accident. This area was chosen because it was the most heavily radionuclide contaminated part of Chiba Prefecture and it neighbors metropolitan Tokyo. Measurements were performed using a 3-in × 3-in NaI(Tl) scintillation spectrometer in June 2015. The survey route covered the whole Tokatsu area which includes six cities. A heterogeneous distribution of absorbed dose rate in air was observed on the dose distribution map. Especially, higher absorbed dose rates in air exceeding 80 nGy h-1 were observed along national roads constructed using high porosity asphalt, whereas lower absorbed dose rates in air were observed along local roads constructed using low porosity asphalt. The difference between these asphalt types resulted in a heterogeneous dose distribution in the Tokatsu area. The mean of the contribution ratio of artificial radionuclides to absorbed dose rate in air measured 4 years after the accident was 29% (9–50%) in the Tokatsu area. The maximum absorbed dose rate in air, 201 nGy h-1 was observed at Kashiwa City. Radiocesium was deposited in the upper 1 cm surface layer of the high porosity asphalt which was collected in Kashiwa City and the environmental half-life of the absorbed dose rate in air was estimated to be 1.7 years.
Highlights
The environmental radiation levels in eastern Japan were dramatically changed after the Fukushima Daiichi Nuclear Power Plant (F1-NPP) accident in March 2011
Higher absorbed dose rates in air of over 80 nGy h-1 were observed along national routes (NRs) 6 and 16 that pass through Matsudo (#5 in Fig 1B), Kashiwa (#3 in Fig 1B) and Abiko (#4 in Fig 1B) Cities
While the absorbed dose rate in air just after the accident had shown a homogeneous distribution in the Tokatsu area, it was a heterogeneous distribution
Summary
The environmental radiation levels in eastern Japan were dramatically changed after the Fukushima Daiichi Nuclear Power Plant (F1-NPP) accident in March 2011. According to the UNSCEAR 2013 report [1], the released total amounts of artificial radionuclides were estimated to be 6–20 PBq of 137Cs and 100–500 PBq of 131I and they are about 20% and 10% of the PLOS ONE | DOI:10.1371/journal.pone.0171100. Distribution Map of Absorbed Dose Rate in Air in Tokatsu Area, Chiba no patents, products in development or marketed products to declare. This does not alter our adherence to all the PLOS ONE policies on sharing data and materials. Since the F1-NPP accident, distributions of absorbed dose rates, affected by artificial radionuclides, have been observed by public officials and researchers [2,3,4,5,6,7]. In the most extensive surveys, the Japanese government has carried out air- and car-borne surveys centered on Fukushima Prefecture at regular intervals, and the distribution maps of dose equivalent rate have been made available on the website of the Nuclear Regulation Authority, Japan [8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
