Nine months after the disaster, the Japanese Science Ministry finally gave birth to a report about radiation spread across Japan, as published by Asahi Shimbun newspaper (article also reproduced below). Although from the relatively small size of Japan compared to Chernobyl-stricken Belarus, it was obvious from the onset that Cesium would fall “all over Japan” (breaking news title from the Asahi Shimbun article), the issue was to assess concentrations.

Since the Japanese government policy remains to downplay the risk, after censoring radiation reports in the news and in the blogosphere, data should be taken with a grain of salt. Last week, the Japanese government has turned its back on the company it had contracted to monitor radiation in parks and school playgrounds around Fukushima, after it suddenly discovered that the accuracy of the Geiger counters it had ordered was substandard (Cf. Mainichi Shimbun news article and comment in Geiger Counter Case Study: Inspector Alert in SurvivalJapan). MEXT data for all regions but Fukushima falsely reported radiation levels close to natural background radiation for months so that I only trust citizens reports such as Safecast. On the Japanese government radiation map below, it is a safe bet to assign to each concentration the level range above each reported, i.e. for 0-10.000 Becquerel/sq.m, the real value is probably between 10.000 and 30.000 Becquerel/sq.m. As for the methodology, only one station per prefecture was used to measure data. The Japanese government and affiliated organizations reportedly used Geiger counters conveniently located to show the least radiation, as in the current case of Tokyo University, which use only their one station with lower readings and switched off the other one which measures higher levels of radioactivity. Japan is not the only country to set their radioactivity monitoring stations at their convenience, this is common practice as shown in France by CRIIRAD with Areva (ex-COGEMA) company for instance, in the context of nationwide contamination from closed uranium mines. Read for instance “Decommissioning Projects – France” on Wise-Uranium with links or directly the English report by Head of CRIIRAD Bruno Chareyron, “Radiological hazards from uranium mining”, available for download in PDF format. CRIIRAD stands for Commission de Recherche et d’Information Indépendantes sur la RADioactivité / Commission for Independent Research and Information about RADiation and Bruno Chareyron was invited in Fukushima.

If absolute figures are probably fudged, relative concentrations of radiation in cities are likely to be trustful (although it says nothing about other cities in each prefecture). Hereafter is a ranking based on the news article, with lowest concentration rounded up to 1 Bq/sq.m for Uto, Kumamoto Prefecture, as the reported value is unrealistically small (0.378 Bq/sq.m) and for the sake of having a non-null integer multiplier. It should be noted that the apparent precision of figures is misleading and I kept the 2 most significant figures for this short ranking:

Kumamoto (Kyushu) : 1

Osaka : 20

Tokyo : 20,000

Yamagata (Fukushima and Miyagi neighbor by the Sea of Japan) : 20,000

Ibaraki (northern neighbor of Tokyo by the Ocean Pacific) : 40,000

In other words, radiation is 10 times lower in Kyushu compared to Kansai (suspiciously, in spite of the Genkai nuclear incident, Cf. Nuclear Incident in Kyushu November Update on SurvivalJapan). Kansai is itself a 1000 times less irradiated than Tokyo. This seems about right and there is of course a gradient between these regions. Indeed, before information black-out was enforced, a Japanese green tea grower in Shizuoka (further south from Mount Fuji, about 150 km / 100 miles south-west of Tokyo) reported high level of radioactivity (read for instance the New York Post article about it). In order to get 680 Bq/kg in dried tea leaves, as was reported there in Honyama area, the soil needs to be pretty contaminated and hence also the air, from which radioactive fall-out precipitates (therefore, other food products from this wider area are contaminated as well). This means that statements like the following one is untrustworthy: “Large amounts of radioactive dust fell in Tokyo, but a separate survey has detected relatively low accumulations of cesium in the soil.” Actually, it was documented in the US in the wake of a nuclear bomb test in Nevada that decontamination of roads and concrete surfaces is impossible even by using hydrochloric acid, so if the latter sounds paradoxical with regards to “large amounts of radioactive dust fell in Tokyo”, then it is another lie by the ministry official : “Tokyo has smaller soil surfaces than other prefectures, but road and concrete surfaces are less prone to fixate cesium deposits, which were probably diffused by the wind and rain”. Read “Secret Fallout” by Dr. Ernest Stainglass available for download in PDF format for more information about the myth of nuclear decontamination and more specifically chapter 1, “Thunderstorm in Troy”.

Likewise, it is just simply impossible to reconcile statements of Ibaraki prefecture being 1 million times more radioactive than 2 years ago on one hand, and the current air radiation level being 0.14 uSv/h, i.e. what I personally measured in my city in the monitored area and which is an ordinary value indeed. Again, the same article mentions that Ibaraki is more than 40,000 times radioactive than Kumamoto in Kyushu (actually 100,000 if we consider the exact values given in the article). It is a wonder that such inconsistencies can exist in an article from a mainstream newspaper without a word of critical analysis. The article leaves a great grey area between Tokyo and Osaka – as it would be interesting to get some values for Nagoya for instance, which is inside the no man’s land in my book (although the Aichi prefecture is supposedly “clean” on the map below), as one needs to draw a line somewhere and radiation reports by citizens were higher than “normal” there.


Note: real values probably one notch higher in the scale

Asahi Shimbun – Cesium from Fukushima plant fell all over Japan

November 26, 2011

Radioactive substances from the crippled Fukushima No. 1 nuclear power plant have now been confirmed in all prefectures, including Uruma, Okinawa Prefecture, about 1,700 kilometers from the plant, according to the science ministry.

The ministry said it concluded the radioactive substances came from the stricken nuclear plant because, in all cases, they contained cesium-134, which has short half-life of two years.

Before the March 11 Great East Japan Earthquake, radioactive substance were barely detectable in most areas.

But the Ministry of Education, Culture, Sports, Science and Technology’s survey results released on Nov. 25 showed that fallout from the Fukushima plant has spread across Japan. The survey covered the cumulative densities of radioactive substances in dust that fell into receptacles during the four months from March through June.

Figures were not available for Miyagi and Fukushima prefectures, where the measurement equipment was rendered inoperable by the March 11 disaster.

One measurement station was used for each of the other 45 prefectures.

The highest combined cumulative density of radioactive cesium-134 and cesium-137 was found in Hitachinaka, Ibaraki Prefecture, at 40,801 becquerels per square meter. That was followed by 22,570 becquerels per square meter in Yamagata, the capital of Yamagata Prefecture, and 17,354 becquerels per square meter in Tokyo’s Shinjuku Ward.

The current air radiation level in Ibaraki Prefecture is about 0.14 microsievert per hour, equivalent to an annual dose of about 1 millisievert, the safety limit for exposure under normal time international standards.

Large amounts of radioactive dust fell in Tokyo, but a separate survey has detected relatively low accumulations of cesium in the soil.

“Tokyo has smaller soil surfaces than other prefectures, but road and concrete surfaces are less prone to fixate cesium deposits, which were probably diffused by the wind and rain,” a ministry official explained.

The fallout densities were considerably lower in the Chugoku and Kyushu regions in western Japan. The smallest figure of 0.378 becquerel per square meter came from Uto, Kumamoto Prefecture. The density in Osaka was 18.9 becquerels per square meter.

The peak value in Ibaraki Prefecture was 970,000 times larger than the cumulative fallout density of 0.042 becquerel per square meter in fiscal 2009, found in an earlier nationwide survey before the Fukushima crisis started.

Before the accident, cesium-137, which has a longer half-life of 30 years, had been detected from time to time from atmospheric nuclear tests. But those densities mostly stayed below 1 becquerel per square meter, while cesium-134, with a shorter half-life, was rarely detected, the ministry officials said.

Also on Nov. 25, the science ministry released maps of aerially measured radioactive cesium from the Fukushima plant that accumulated in Aomori, Ishikawa, Fukui and Aichi prefectures.

This was the final batch of the 22 prefectures in eastern Japan where mapping was to be completed by the end of this year.

Nowhere in the four prefectures did the accumulations exceed 10,000 becquerels per square meter, the threshold for defining an area as being affected by the nuclear accident. This reconfirmed the science ministry’s view that radioactive plumes wafted only as far west as the border of Gunma and Nagano prefectures and as far north as the border of Miyagi and Iwate prefectures, ministry officials said.

The ministry also confirmed that radioactive plumes tended to drift just short of mountain ranges where they formed belts of high cesium concentrations due to rainfall and other factors. The mountain ranges included the Ou and Iide mountains along the border of Yamagata and Fukushima prefectures, the Echigo mountains along the border of Fukushima and Niigata prefectures, the Shimotsuke mountains along the border of Fukushima and Tochigi prefectures, and the Kanto mountains along the border of Gunma and Nagano prefectures.

These patterns are shown in three-dimensional plots in an online Japanese-language document released by the science ministry (

The ministry also said Nov. 25 that it will conduct aerial measurements of cesium accumulations in soil in regions outside the 22 prefectures starting next year. That is because small amounts of cesium have been detected in dust deposits in Hokkaido and western Japan.


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