Archive for the ‘Radiation Maps’ Category

The coast of the Sea of Japan is illuminated by a string of nuclear power plant reactors which is locally known as the Nuclear Ginza, after the name of a dazzling international shopping area in Tokyo. Three months ago, in our post Shiga Nuclear Disaster Simulation Pulled Off NHK News, SurvivalJapan introduced the attempt by Shiga prefecture to simulate the effects of a nuclear disaster in one of these reactors, for instance the troubled Mihama where a water leak occured just last week as reported in Mihama Reactor Shutdown Update 1 on SurvivalJapan.

Shiga is on the eastern border of the monitored land, i.e. the safer part of Japan where anything might happen and which needs to be carefully monitored, as explained in Japan Livability Map September 2011 and in our later posts. Shiga capital city is Otsu, at the southernmost tip of the Lake Biwa (or Biwako) which provides the region with tap water, including neighboring Kyoto city. Maps of Shiga and of the nuclear fallout which would result from a disaster at Mihama are available in Another Troubled Nuclear Reactor Shuts Down on SurvivalJapan.

Asahi Shimbun just published an article of difficulties that Shiga prefecture faces in getting access to the nationwide SPEEDI nuclear simulation data – the system which results were ignored by the government in the aftermath of March 11, as then Prime Minister M. Naoto Kan chose to apply an unsophisticated geometrical circle rule around Fukushima ground zero instead. It is telling that a prefecture cannot have access to some SPEEDI data but that pro-nuclear Yomiuri Shimbun could – and quickly at that – and used it to calculate some radiation dose in the wake of Fukushima disaster, as reported in their March 27 article titled Radiation doses spread unequally / Experts say govt should give more detail in designating evacuation zones.

The article is reproduced below and illustrates that although the Japanese population gives some signs of changing its opinion and that some prefectures get the clue of this political shift, the Japanese government has yet to feel it and adapt. Also it is a reminder that a technologically advanced country such as Japan may have everything it needs to simulate and forecast issues; monitor radiation and efficiently communicate about it; display unique humanoid robots and rescue teleoperation machines; move seamlessly people around and quickly build housings – it is all for nothing without proper political leadership.

Last, it is made clear that the concern of the Japanese government, more specifically of its MEXT and METI ministries, is not to avert another Fukushima-style disaster but to keep the nuclear energy sector afloat. As mentioned in earlier posts, the CIA has been pushing for this since the fifties through Yomiuri Shimbun (actually much more than just a newspaper) and the main Japanese nuclear companies are joint ventures with American companies (GE Hitachi Nuclear Energy and Toshiba Westinghouse). This blog engine being American, SurvivalJapan should remain quite safe if certain industrial interests are not discussed here, even though they are in the public domain. Most blogs about Fukushima nuclear disaster hosted in Japan have been pulled off-line so I will simply invite the interested reader to Google it up for herself (some extra keywords: Gregory Jaczko, Matsutaro Shoriki, Bill Magwood and why not a recent article by Yomiuri Shimbun itself titled U.S. to restart construction of N-reactors / Toshiba arm to deliver new model to better understand why there are almost no report of nuclear fallout from Fukushima in the US – enough said).


A lot of the rationale of supporters of non-evacuating Tokyo seems to revolve around the notion of hotspots. Hotspots are limited areas in which ground radiation spikes up compared to the surroundings. Although radiation is not negligible in Tokyo, some argue that it is even higher in similar cities where there hasn’t been any known nuclear incident, such as Hong Kong with more than 0.3 uSv/h at 1m above ground. Tokyo hotspots detected in Setagaya, around the Imperial Palace, etc. were not very satisfactorily explained in the news by the supposed presence of radium bottles left over (same explanation used several times).

Tokyo cityscape changes continually and buildings may disappear suddenly as one visits a street after a few years. Besides construction work and demolitions, low to medium intensity earthquakes regularly shake the city and cause shelves, TV sets, etc. to fall and smash on floors. It is difficult to imagine radium bottles lying around for 50 years untouched in these ever-moving conditions. Such bold statements from the government were largely accepted by the population who is eager to cling to any reassuring explanation for their hotspots.

Hotspots are perceived to be like rotten apples in an otherwise healthy basket, singularities which statisticians can dismiss in order to focus on the average radiation environment. Scarcity of hotspots seem to support this view, however monitoring is imperfect and reporting even worse.

Shortly after March eleven, a green tea grower from Shizuoka prefecture (south-west of Tokyo and near the Mount Fuji) reported that his tea was radiation-hot after he got it analyzed on a voluntary basis (Cf. link to New York Times story in Analysis Of Japanese Government Radiation Spread Report on SurvivalJapan). Panic followed among green tea growers who made sure that none of them would ever carry their tea leaves to a laboratory again. This is anecdotal but it illustrates how hotspots are discovered and buried in Japan. Therefore hotspots tend to seem isolated whereas, if the population wanted to seriously investigate, there might be more rotten apples.

Here is another anecdote: in the farming village from where I buy local vegetables and rice, I proposed a foreign friend of mine who grows organic food there to make some radioactivity measures – and in order to make it significant, to get organized with the local Japanese community and offer to check out their fields and rice paddies too. My friend replied that such discussions had already taken place and that the consensus was that, although it would nice to know that the soil is safe, it would have a devastating effect with commercial consequences, should we find anything unusual. I discreetly made a measurement there which showed it was alright (0.125 uSv/h with Inspector Alert right next to the wet, black soil) and told my friend about it. From reading the news and hearing people talks, I am convinced this is a relevant example of farmers’ attitude with respect to radiation monitoring nationwide – and hence the explanation of the scarcity of reported hotspots.

Hotspots monitoring in Japan is like searching for a sick tree at the edge of a forest, cutting the tree down and never look in this place again. (more…)

Fukushima is the primary source of atmospheric radioactive material fallout. Radioiodine, which disappears rapidly, is regularly detected and shows that criticallity is still happening. Melt-through in three reactors and total lack of control and knowledge about conditions by TEPCO would make it at least three times worse as Chernobyl – yet this has still to become common sense and most people in north-eastern Japan try to reassure themselves that it is still safe until the fourth reactor blows up, which is only a matter of time. Tokyo should have been evacuated immediately and forever – after 8 months, an orderly evacuation could have been carried out and housing built but the Japanese government and mostly the population, who lives in denial, decided otherwise.

Usually SurvivalJapan leaves Tokyo out of the picture as anyone serious about their survival in Japan would have left the no man’s land area, including Tokyo, long ago. However, M. Goshi Hosono’s plan to spread radiation all over Japan is making its way, with potential effects outside the no man’s land, in what we call the monitored land, as can be read in the Japan Today article below and which was already mentioned on SurvivalJapan almost 3 months ago in Tokyo Imports 500,000,000 Kg Of Nuclear Waste.

Incinerators are less than 4 miles away from the Imperial Palace and popular places like Shibuya and Ebisu, which will all be under the radioactive fallout when winds abate.

I am told that yakuza are different from other similar organizations worldwide, as they supposedly appeared first to protect outcasts and organize work for them, and are nationalists who want to protect Japan and the Imperial Family. Mothers who occupy Hibiya Park in Tokyo (close to the Parliament, the Imperial Palace and headquarters of many large dysfunctional companies such as TEPCO and neighbor Mizuho) reported that harassment from right-wing militia somewhat relented when mothers told them that they would pack up their camping tents and leave if His Majesty would meet with them and ask them to. There are a few public enemies in the government, firms and media nowadays who are jeopardizing Imperial lives and the future of Japan – one can only wonder what yakuza associations are waiting for before saving this country if nobody else will, not that I am suggesting anything.

Winds will carry radioactive smog towards Chiba peninsula and Izu peninsula and archipelago depending on the season and weather. Winds seldom blow west but they occasionnally do, as Meteocentrale wind simulations show, and they sometimes even reach Osaka from Fukushima. The flying distance between Tokyo to Osaka (250 miles) is about the same order as between Fukushima to Tokyo (150 miles), although slightly less and Tokyo is a secundary source, not exactly like Fukushima itself.

Besides, the terrain configuration around Tokyo, i.e. the Kanto Plain, is unfortunately perfect to drive radiation fallout as we surmised from March eleven and was later proven by the presence of hotspots in Gunma, Saitama, etc. Further west, the region of Nagoya, in Aichi prefecture, will be also affected as well as the whole Nobi Plain, although less than the Kanto Plain of course. The whole coastal area between Tokyo and Nagoya, i.e. Shizuoka, etc. will be on the way on adverse days. Radioactive winds can also easily go through between Shiga and Mie prefectures, where mountains are low and several valleys let highways through to Osaka.

Japan Today – Tsunami debris from Miyagi to be incinerated in Tokyo this week

Dec. 13, 2011 -


The first load of tsunami debris from Miyagi Prefecture will be test burned at a waste incineration plant in Tokyo’s Ota Ward on Tuesday and Wednesday, with further tests scheduled for Dec 20-21 at a Shinagawa Ward plant.

If the test burns go well, large-scale burning will commence next February at a rate of 150 tons per day, Tokyo metropolitan government officials said, Fuji TV reported. Under the plan, 10,000 tons of combustible debris from Onagawa will be disposed of in incineration facilities located on reclaimed land in the Tokyo Bay area.

Officials plan to burn 500,000 tons by 2013.

Miyagi, Iwate and Fukushima prefectures have massive mountains of rubble, said to weigh more than 23 million tons.

The debris being sent to Tokyo is mainly wood and metal. By the end of next March, Tokyo will have received a total of 500,000 tons of debris from Miyagi and Iwate prefectures.

This article may still be available from its original source.

Elections in Osaka brought a new radioactive waste incineration top supporter in the person of M. Hashimoto, in line with the previous government and closer to achieving their plan. Foreigners are leaving Japan for both economical and radioactive contamination reasons and some of the lingering companies are looking to the west to seek refugee but local politicians do not understand that they are planning to kill Osaka and reject foreign investment in their city and the whole Kansai region – and accelerate the overseas shift of major domestic manufacturers based in the area. Downsizing in foreign companies in Japan – starting with the repatriation of expats – may not be obvious in statistics yet, but the situation is incredibly tense and this kind of “atmospheric intelligence” will become supported by hard economic data next year. Therefore, the Osaka Governor should guarantee the security of international staff and take all necessary measures to ensure that radioactive waste is refused if only in order to keep foreign companies in Kansai and attract more of them.

According to the Kansai Bureau of Economy, Trade and Industry (METI), the Kansai region accounts for approximately 20% of Japan’s economy, the equivalent to that of the Netherlands (ranking 17th in the world) – Source: 2009 Kansai Keizai Hakusho (Economic White Paper). The website of the German Chamber of Commerce and Industry in Japan states that:

“Apart from Tokyo, the Kansai region in western Japan is the most important economic centre. The Kansai region groups the seven prefectures of Fukui, Shiga, Kyoto, Osaka, Hyogo, Nara and Wakayama, and covers 8.3% of Japan’s surface area. Its approximately 24 million inhabitants produce 16% of Japan’s GDP. Its share of total Japanese exports to Germany is 22.6%, and of imports from Germany 17.4%.

The Kansai region boasts a gross regional product of $US770 billion, which corresponds to an economic strength on a par with Canada, or with South Korea, Taiwan and Singapore combined.”

Kansai is the only large economic region in Japan striclty outside the no man’s land and previous Prime Minister Naoto Kan once considered the possibility of moving the Japanese government to Osaka – yet Osaka Governor decided to destroy it anyway.

US and Germany represented respectively 33 and 16% of all foreign-affiliated companies in Kansai by country in 2008, according to The Foreign Investor CD-ROM 2009, by Toyo Keizai Inc. – that is a combined half of all these foreign companies. As soon as the radioactive disease comes to Osaka, these companies will shrink like their Greater Tokyo sisters. Furthermore, the latter will cancel any plan they might have had to move at least part of their staff over there.

If you are a potential expat from the US, Germany and any other English-fluent national, I strongly caution you against accepting any position in Japan at the moment, since Tokyo is actually within the real no man’s land – except that it is officially miraculously spared from Fukushima, much like Minsk is supposed to be from Chernobyl, within similar distances; Osaka is on the verge of falling into the shadow and Nagoya will surely follow its path once Osaka is taken. The Osaka Chamber of Commerce and Industry may well issue some reports that the situation is safe and organize special events to promote it, it will not be safe and foreigners know it. Indeed, would you accept working in Minsk or Kiev (no offense to residents and victims of these cities)?


Tokyo-based citizen radiation monitoring group Safecast published a map of radiation levels in Kyoto city. The map includes areas such as the Kyoto incinerator plant, where radioactive waste could be incinerated if Hosono got his way in spite of local opposition; Kyoto JR train station; popular tourist spots such as the park of the imperial palace;  nearby farming village Ohara, etc. It was “safecast” by a bicyclist at 1 meter above ground level yesterday. To our knowledge, this is the first map in Japan made in the monitored land as Safecast understandably focus on radiation levels in the no man’s land. Hopefully other cities such as Osaka, Fukuoka, etc. as well as nuclear plants such as repetitively troubled Monju will follow.

Levels are within 35 to 70 CPM (count per minute), i.e. between about 1 to 2 mS/year. Although these levels are twice as expected, they are harmless even for residents, therefore all the more for short-stay visitors. A screenshot of the map is reproduced below.


This post is an update of Geiger Counter Case Study: Inspector Alert published on SurvivalJapan in which some questions remained open, mainly about the relatively high values (although still in the safe range) which I measured with the system kindly lent to me by Safecast and from whom I received some further advice.

The Safecast bGeigie system is designed to measure mainly gamma rays (high energy protons, akin to X-rays) and hence is used at least one meter above ground in their radiation maps. Since I live in the monitored land, several hundred miles away from Fukushima, gamma radiation is low and not really a concern. Therefore I had measured instead beta radiation (high energy electrons or positrons which are emitted back from the ground after radioactive fall-out) at about one foot above ground. For convenience, I monitored the level of radiation with the Safecast display which communicates by radio with the Inspector Alert safely cast in its lunchbox style (in Japanese “bento”) box, along with the GPS and SD memory card to geo-locate and store results. The Safecast team advised against this methodology for beta radiation pick-up and advised me to use the Inspector Alert alone for that matter – which I did.

I read the user manual to set the Inspector Alert display in uSv/h as opposed to CPM (count per minute) as I am more familiar with this unit and it is more relevant for body effects. The user manual explains that the factor used by the device to convert CPM into uSv/h is based on Cesium-137, the radionuclide used for its calibration, so the uSv/hr display is less accurate for other nuclides (such as Cesium-134, Strontium-90, Iodine-131 and of course Uranium and Plutonium…). This is why Safecast uses the CPM raw data instead.

The first measure that I made was inside my home and the display changed widely even in a single place. A Geiger counter is not like a weighing scale: it does not give a result at once nor does it give a stable result. Therefore when a value is broadcast either by citizens or a governmental organization, it should be taken with a grain of salt. For instance, I could measure 0.120 uSv/h and any value between 0.090 and 0.150 uSv/h, that is about 25% more or less than the central value. Sometimes, some wilder values would come up: how do we interpret these?

Radiation is a random phenomenon which occurs naturally, so when a particle hits the Geiger counter sensor plate, it is registered and changes the overall measure value. The Inspector Alert averages measures over 30 seconds in order to get a more statistically relevant measure. Even then, the result is only displayed every 3 seconds so if one is moving, there is a delay between the measure and the display. Then there is the 15% accuracy which is probably an average: it means that some wild values (standard deviation) can occur from time to time. Other factors which can affect the results are solar flares (there was just a sunstorm by the way) and, probably, thermal drift if the device electronics is not properly compensated when temperature changes (any kind of electronics sensor is subject to this phenomenon). The bottom line is that measures could be twice as high depending on temperature, solar activity, randomness of natural radioactivity, types of radionuclides (including artificial ones from nuclear plants) and radiation (here it is a synthetic result of alpha, beta, gamma and X-rays), accuracy, resolution, etc.

Indeed, I could still measure inside and outside values from 0.055 to 0.225 uSv/h and even up to 0.355 uSv/h when spot on granite blocks which are naturally radioactive. These new measures were consistent with the range I had already measured with the full Safecast system. I could also check that the outer casing of Safecast suitcase and bento box did not emit stronger radiation than the room so the Geiger counter is likely not contaminated (and there should not be any calibration issue either according to the user manual).

I still could not double-check with another type of Geiger counter yet but these new results convinced me that they are normal. The maximum international value (except in post-Fukushima Japan) accepted is 1 mSv/year, which equates to 0.114 uSv/h. Given a 15% accuracy, it means that the Inspector Alert should read between 0.097 and 0.131 uSv/h which is indeed what it does most of the time (so we can dismiss occasional lower and higher results as products of standard deviation).

A final word of advice which I received from Safecast and which is also documented in the user manual is to use the timed count function of the Inspector Alert over at least 10 minutes to further smooth out results. There should be about 15% difference maximum between two such timed counts.

I hope that this update helps you to get a better idea about the capabilities and limitations of Geiger counters in general and specifically of the Inspector Alert – and of the analytical mindset and of the basic radiation knowledge necessary to properly use them. In any case, purchasing a Geiger counter to try and measure radioactivity in food does not make any sense (unless the food is irradiated to such a level that just staring at it is dangerous) and that monitoring the food trace is a safer and more reliable procedure. Thankfully, this is getting easier.

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.