Choosing an appropriate Geiger counter to monitor environmental radiation levels in Japan can be confusing due to the large choice of devices, including handheld electronic dosimeters that offers similar capabilities. Counters differ by the type of radiation that they can detect (alpha, beta, gamma, X-rays and sometimes even neutrons), their accuracy, price, availability, etc. Rather than presenting an extensive comparison between all devices, this post introduces a specific Geiger counter used by Safecast to map radiation mainly in the no man’s land: the Inspector Alert distributed by International Medcom (SurvivalJapan has no interest in promoting this company, this review is purely on a volunteer basis and I decline all responsibilities as to opinions shared here). It is also the device used by Pr. Frank Daulton, Ph.D., Applied Linguistics, Ryukoku Univ., Kyoto, Japan when he detected 0.377 uSv/h close to ground around his home in Otsu-City, Shiga Prefecture, not far from Kyoto and 311 miles (500 km) from Fukushima (his picture reproduced here) as reported on Earthfiles website.
Inspector Alert detects alpha, beta, gamma and X-rays which is more than enough in the monitored land where radiation is mainly from beta source (high energy electrons or positrons) in the ground due to precipitations. Gamma rays are a minor contributor due to the distance from Fukushima. Still the device combine the 4 types of radiation and gives a synthetic reading.
Accuracy is 15% for the low levels of radiation that we can measure in the monitored land. This important parameter is seldom mentioned in reports. Although the precision from the display seems to imply a resolution to the nSv/h (0.001 uSv/h), this is of course not true as with any kind of sensors. In the example of Pr. Daulton in the picture above, 0.377 uSv/h on the display could mean anywhere between 0.320 uSv/h and 0.434 uSv/h. Every Geiger counter has a specific accuracy, often less precise than this device, typically 20%. In the case of Geiger counters ordered by the Japanese government to the firm Alpha Tsushin K.K. for some 370 million yens for schools near Fukushima, accuracy was 40% – it is however a controversial affair and the government cancelled its contract (the controversy being whether the government had initially ordered defective counters for media purpose). This is documented in an Mainichi Shimbun article, reproduced at the end of this post. Back to the topic of accuracy, not that all three digits are relevant: for instance, it does not really matter that the reported reading is 0.320, 0.377 or 0.434 uS/h – especially given the accuracy. The meaningful information which this reading gives us is that radiation is between 2.8 and 3.8 mS/year – or 3 to 4 times what it should have been. Even so, this does not make Otsu a dangerous place to live in. As we can see, accuracy, resolution and annual mean are important in order to make an educated decision of actual risk. This is further complicated by the fact that the instrument might not be properly calibrated anymore, after a certain usage.
Calibration is normally done and geiger counters are usually ready to be used when shipped, as is the case with the Inspector Alert. However, they can lose their calibration over time: this means that even in absence of any radioactivity, the counter might display a value which is not zero – or close to zero depending on the normal background radiation, for instance 0.05 uSv/h. Another case for such “offset” can be when the counter has been contaminated with radioactive dust, if it was used without any protection to its sensitive screen: the Inspector Alert has a 2-inch (5 cm) “pancake” GM sensor in which dust can easily settle for good.
I could carry some tests with an Inspector Alert lent to me and the default value was 0.160 uS/h which is a little higher than I expected. Since it had been used most probably in the no man’s land near Fukushima, I first bought a pair of dish-washing gloves, an efficient paper face-mask (“99% of dust stopped, including viruses!”) and a fine and soft dust cleaner at a 100 yen shop and gently cleaned it outside. I threw the cleaning set away in a convenience store dustbin and used the Geiger counter in its protective casing. A thin aluminum sheet in front of the pancake allowed radiation to come in while preventing contamination. I had this dusted as well and noticed that a tear in the aluminum had been fixed with some heavy duty tape, which could mean that some contamination had occured at one point. I measured radiation 20 cm above ground during 2 hours and the results were mostly in the range of 0.12 to .20 uSv/h. When I turned the pancake close towards my chest, the reading was 0.16 uS/h outside as it was inside my home with the counter used normally. Without being too specific, there isn’t probably any radon gas at my place. This little experiment requires some critical analysis: it seems indeed that there is a relatively strong offset with this particular device, as I doubt that either me or inside my home is that radioactive. In Japan, there is very little granite as the archipelago is of volcanic origin, so the background radiation prior to Fukushima and other nuclear incidents was lower than in many places worldwide. Safecast even claim that Hong-Kong is more radioactive than Tokyo even after Fukushima on their FAQ page. Therefore, the normal background radiation could be expected to be near the typical value at sea-level, i.e. 0.05 uS/h. Most Japanese cities are built just a few meters above sea-level, so it could be slightly higher, say 0.06 uS/h. Even if the accuracy margin increased the reading by 15%, it should still be around 0.07 uS/h. So either the background radiation is three times as normal or the counter has been contaminated or decalibered. This is one of the reasons why a single individual or laboratory should not be the basis for conclusions: several measurements should be carried out with different types of devices and people in order to get a statistically relevant sample set. In case of alarming figures, measurements should definitely be double-checked by someone else, preferrably with another kind of counter, before making panicky decisions.
My experiment also allowed me to check that radiation readings are indeed different at 20 cm above ground (less than a foot) compared to 1 m (3 feet) or even twice this altitude – it decreases further away from the ground. Of course, radiation above sand, which is typical on Japanese playgrounds, is slightly higher. Measuring radiation properly suppose a minimum of metrological knowledge. Still results remain in the same overall range.
All in all, it seems that Inspector Alert does a good job (detailed specifications are available on the link above) and the strong yen makes its 800 USD price a little less expensive in Japan than it used to be – however I am glad that I could borrow it. Safecast Submit page gives a list of websites where to purchase it. Interestingly, the only International Medcom reseller in Japan, according to their webpage, is an obscure company called Uchida Yoko which website does not seem to offer this product.
For anonymity reasons, I cannot share my location in this post, but I felt reassured that the preliminary levels which I measured were relatively harmless – and I checked in all playgrounds where our kids might play. If the levels reached twice the yearly worldwide (except in post-Fukushima Japan) maximum limit, i.e. 2 mSv/year, the equivalent hourly rate would be 0.23 uSv/h. This is, according to a Fukushima Diary post, the official “decontamination limit” around Fukushima but I could not verify this information yet. According to the Inspector Alert Manual downloadable from International Medcom website in PDF version, calibration should not be needed and radon cannot be directly detected – so that would leave only room for contamination or actual relatively high radiation (still, under this so-called “decontamination limit” even with allowances made for accuracy).
For some perspective, 2 mSv/year is a tenth of male nuclear plant workers maximum authorized exposure (except in post-Fukushima Japan…); however, it is also 4 to 5 times the natural exposure of someone who does not live in a radon-filled house and has little use for medical X-rays and continental flights; it isn’t outrightly dangerous yet it isn’t the best environment, especially for kids, either.
This conclude this case study. Videos and websites can easily be found with “Inspector Alert” search terms. Personnally, I look forward to double-check my results.
Read also latest Inspector Alert Study Update on SurvivalJapan.
Mainichi Shimbun – Fukushima radiation meters fail gov’t accuracy requirements
Radiation meters installed at parks and primary schools across Fukushima Prefecture do not meet the central government’s minimum accuracy requirements, it was learned on Nov. 18.
The Ministry of Education, Culture, Sports, Science and Technology cancelled its contract with the meters’ supplier the same day. The ministry will begin removing the 600 devices soon, and reopen bidding on the radiation meter contract. The meters were scheduled to start operating in October, but that has now been pushed back to February next year at the earliest.
According to the ministry, five firms bid on the meter supply contract in July, won by Tokyo-based telecommunications equipment firm Alpha Tsushin K.K. for some 370 million yen. The contract requirements demanded that radiation measurements be accurate to within plus or minus 20 percent, but soon after they were installed in October the ministry discovered the meter readings were off by as much as 40 percent.
The science ministry intends to demand compensation from Alpha Tsushin for breach of contract.
A public relations official with the company told the Mainichi, “There are many points on which we cannot agree with the cancellation of the contract.”
(Mainichi Japan) November 19, 2011