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.
Levels could help give an indication as to the trustworthiness of government data. Asahi News reported that the official read-out for nearby Osaka was 18.9 becquerels per square meter (Cf. Analysis Of Japanese Government Radiation Spread Report on SurvivalJapan). I found a conversion formula widespread on the Internet however I could not verify it from a trustworthy scientific source so please use caution with the following comparison: 1 Bq/cm2 would be equivalent to a 1.319 uSv/h skin exposure dose – in other words, 1 Bq/m2 to 0.0001319 uSv/h (using non-scientific notation on purpose). Hence the density in Osaka would correspond to an equivalent dose of 0.0025 uSv/h. Since the natural background radiation is at sea level typically around 0.05 uSv/h (or 380 Bq/m2), it seems that there is something wrong either with the formula or with official data – or more likely both. According to the same article / report: “The smallest figure of 0.378 becquerel per square meter came from Uto, Kumamoto Prefecture.” – if the formula was right, since this is a thousand times less than the natural background radiation, it would prove to be a ludicrous statement. Another possibility would be that the reporter has got his units mixed up, as this was often the case in first news reports after March 11 (hopefully I am not the one mistaken here). However, in that case, revised upward with a factor 1000, the value of Tokyo would be 17,354 MBq/m2, which is equally absurd. In fact, since Becquerel is the unit for the number of disintegration per second, it could be transposed in uGy/h through the CPM rate, Geiger sensor surface, etc. – that is the formula would be different for each Geiger counter as opposed to a universal one. Indeed, notwithstanding that it is not an authoritative source by any means, Wikipedia article about Becquerel does mention the following, in the paragraph titled “Bq versus counts per second”:
“When measuring radioactivity of a sample with a detector, a unit of “counts per second” (cps) or “counts per minute” (cpm) is often used. Some radiation detectors are calibrated in “disintegrations per second” or “decays per second.” All of these units can be converted to the absolute activity of the sample in Bq if one applies a number of significant conversions that take into account the radiation background, the detector efficiency, the counting geometry, the sample size, and the self-absorption of the radiation by the sample.”
Clearly if the relationship between Becquerel and CPS is specific to so many factors, then the formula ought to be a false meme carried by Internet. Sadly, I first encountered it on a blog titled “Education Japan” by “Sean Marsula in Iwate”. Fortunately, comments by readers show that the aforementioned blog is a dangerous fraud, at least when it comes to providing education about radiation, which is exemplified by the blogger’s replies, for instance on April 5th (sic):
“The basic conclusion is that radiaton/radioactivity from Fukushima is essentially certain to have no effect on human health in Tokyo, and if there were any bad consequences, they would be *much* smaller than many other factors (e.g., air pollution, diet, second hand smoke) that affect health.” – heritageofjapan (sic) aka Aileen Kawagoe ?
One of our Kyoto sources who sent 3 local soil samples for analysis reported that Cesium-134 had not been detected whereas “some” Cesium-137 had. We agreed that since the half-life of Cesium-134 is 2 years, there should be some included too if the radioactivity had come only from Fukushima (Cesium-137 half-life is 30 years). My source could check that the levels of radioactivity under his/her house was the same as outdoors, further implying that radioactivity dated from before its construction. Some possible explanations are:
– Fall-out from nuclear bomb tests – yet explosions in the Bikini Atoll (Pacific Proving Grounds) or in Xinjiang, China (Lop Nur nuclear weapons test base near Malan) are equally remote from Japan (at least 3,000 miles). Hawaii is in fact much closer to Bikini.
– Fall-out from Hiroshima and Nagasaki. Hiroshima is less than 200 miles from Kyoto and Eastern winds could easily have carried the fall-out along the southern coast of Honshu (Okayama, Kobe, Osaka, Nara and Kyoto) given the terrain relief.
– Recurrent nuclear power plant incidents in Honshu, some after failed cover-ups by JAPC, as along the so-called “Nuclear Ginza” (Monju, Tsuruga both had radiation leaks and are only 50 miles away from Kyoto; Shika where a criticality incident occurred in 1999 is 150 miles away from it). Some events were probably never uncovered.
Proximity in time and space, i.e. Nuclear Ginza, is probably the most influental factor in the overall contribution of radioactive sources. It should be noted that levels remain very low in all cases and that any city in the world close to a normally functioning nuclear power plant or under the fall-out of nuclear weapon testings would probably present the same or higher radioactivity levels. Central Idaho, for instance, is affected with the highest per capita thyroid dose in the US in the wake of Nevada testings according to the following Wikimedia Commons map (source: US National Cancer Institute). Although this may seem slightly off-topic for a post about Kyoto, Japan, it serves as a relative reference point in our nuclear age and hence carries full relevance in a country from where some might be tempted to run away for lack of a bigger picture.