Reading "National report of Ukraine: Twenty-five years after Chernobyl Accident"

I am reading now a report from Ukraine, "Twenty-five years after Chornobyl accident: Safety for the Future", which can be downloaded from here. (I did not know this until recently:  in Ukrainian, the correct spelling for "Chernobyl" is "Chornobyl". See Wikipedia.)  The reason for my reading of this document is that I wanted to know how the Ukrainian government set the radioactively contaminated zones.  There are four zones in Ukraine: (1) Exclusion zone, (2) Zone of implicit (mandatory) resettlement for more than 5 mSv/year, (3) Zone of guarantee voluntary resettlement for 1 to 5 mSv/year, (4) Zone of enhanced radiation monitoring for 0.5 to 1 mSv/year.

0.5 mSv/year corresponds to 0.06 μSv/h, which is observed everywhere not only in Tokyo, but in many parts in Japan (and maybe in many places in the world).  Usually, 0.06 μSv/h is regarded as a  "low" dose. When this zone classification was reported in NHK (Japan Broadcasting Cooperation), I thought something is wrong: 0.06 μSv/h is too low as a radiation monitoring district. That is why I decided to read the original report by myself.

First of all, I expected that the report is not open to public in the pdf format, so that I thought I might need to go to library to have a copy of the report. But to my surprise, the document can be downloaded in the pdf format! I appreciate those who allowed the download.

Anyway, I read the document, and found that the levels of the "dose" used for the zone classification turned out to be "additional" dose to the natural level. For example, if the natural dose is 0.06 μSv/h, then the No.4 zone (that is, the zone of enhanced radiation monitoring) should show the radiation level from 0.11 to 0.17 μSv/h. I agree that the places in Tokyo and its neighbours showing this level of radiation are surely contaminated by Cs-137, Cs-134, and other radioactive materials from the Fukushima nuclear power plant. My conclusion is that NHK misinterpreted the report issued by the Ukrainian government. As everybody says, it is important to check the original sources or documents so as to obtain correct information and knowledges.

As an example, a place in Chiba (East of Tokyo) shows 0.14μSv/h (with DoseRAE2 dosimeter). This place is near a small lake called "Inba-numa". See pictures and google map, below. The natural radiation level in this place is about 0.03 to 0.05 μSv/h. Therefore, the additional radiation is 0.09 to 0.11μSv/h (0.79 to 0.96 mSv/year), which satisfies the criterion for No.4 Zone.

Left: a view of "Inba-numa"
Right: radiation level measured in the place shown in the left picture.

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 To confirm how much the classification is reasonable, it is useful to measure the radioactivity of the soil in the place. The measurement should be done with the more sophisticated NaI scintillator (of course much more expensive than simple dosimeter such as DoseRAE2 in the above picture). Fortunately, I can access to one of such scintillators (Berthold LB2045), which  measures the radioactivity of soil samples in the unit of Bq (Becquerel, the number of radiation particles per second) . The measured radioactivity of the soil sample taken in Inba-numa is 318.2 Bq/kg (for Cs-137 and Cs-134). The corresponding gamma-ray spectrum is shown in the picture below.

Radioactivity (Caesium 137 and 134) of the soil sample
taken near the Inba-numa lake, Chiba.

The presence of three peaks in the 503 to 1025 keV energy region indicates that this soil is contaminated by Caesium 137 and 134. A small peak near 1550 keV shows a presence of K-40 (potassium 40, a natural radioactive material). CPS for the vertical coordinate means Count Per Sec. The value for Bq is calculated by integrating the spectrum in the relevant energy region. From this result, the 0.14 μSv/h means surely a contamination by Cs-137 and Cs-134.