Radiation fall-out on Tokyo
3rd update of 24 March 2011
This is our third update on the crisis situation in Tokyo, focusing mainly on the radiation risk, and impact on business in Japan. Strong after-quakes are still continuing everyday, more than 300 after-quakes stronger than magnitude 5 were counted since the initial magnitude 9 quake on March 11, 2011 at 14:46.
Loss of human lives (more than 20,000), evacuation (more than 300,000 evacuees), electricity shortages and factory closures have impact on the global supply chains and will impact the GDP of Japan, however we believe there could be a positive impact on Japan’s competitiveness if this crisis leads to structural changes and deregulation in Japan – for details see our interview on BBC.
In the initial phase of the earthquakes mobile phone communications were very unreliable, with voice connections unavailable, and mobile mail connections almost unavailable even in Tokyo, only one mail out of 10-20 attempts could be sent. 3426 mobile phone base stations are reported to be out of action as of March 22 (for an overview of mobile communications including details of base stations see our JCOMM report). SNS on the other hand (Twitter, Facebook, Mixi, GREE etc) were resilient, and we expect their popularity to increase even further because of the quake. Several Japanese Government agencies and Electrical Utility TEPCO started using Twitter the first time a few days after the quake.
Analyzing radiation levels in Tokyo/Shinjuku
Comparing radiation levels in Tokyo/Shinjuku with Austria:
The blue curve above shows the radiation levels in Tokyo/Shinjuku as measured and published by the Tokyo Metropolitan Institute for Public Health here:
each hour for the last 24 hours
daily starting March 1
Before the earthquake on March 11, 2011 at 14.46, radiation data were around 34 nanoGray/hour. Around March 15 and since March 21 increases to the range of 130 – 150 nanoGray/hour where measured. It is generally assumed that these increases are due to radioactive isotopes carried from the Fukushima Nuclear Power station due to wind and weather conditions.
Our Figure shows that radiation levels measured in Tokyo seem to have stabilized with a downward trend. So there maybe some hope for radiation levels to return to normally low levels if the downward trend continues.
To put these radiation levels into context, we compare these radiation levels in the Figure above with the radiation levels naturally found in Austria. The Austrian umweltnet.at website shows current radiation levels in Austria, and mentions that natural radiation levels in Austria are between 70 and 200 nano-Sievert/hour, which corresponds to 70 – 200 nanoGray/hour. We indicate this range above in pink color.
This Figure shows that according to our interpretation, radiation levels in Tokyo/Shinjuku were about 30% lower than the lowest radiation levels found in Austria, and are currently increased to levels which would be in mid-range of natural radiation in Austria (natural radiation is mainly caused by Radon gas diffusing out from the ground, and from the natural cosmic radiation from space). Humans have been exposed to this natural background radiation ever since life exists on earth, and Darwinian evolution of human live has taken place in coexistence with this natural background radiation, and in the natural presence of a corresponding amount of radioactive isotopes.
It is important to keep in mind however, that the radiation levels in the Figure above are due to radioactive isotopes, mainly Iodine (I-131, I-133), and Cesium (CS-134, CS-137), but also Tellurium (Te-132), Xenon (Xe-133) (for a detailed analysis see the AIST data). Detailed impact on people depends on how these isotopes enter the body and whether they remain inside the body, and which organs they affect.
Another factor is 1/2-life. Radioactive isotopes decay with time via emission of radiation, in the case of I-131 8 days, I-132 2.3 hours, and I-133 21 hours. Therefore the Iodine isotopes disappear naturally after a few days, while Cs-134 (1/2-life 2.1 years), Cs-137 (1/2-life 30 years) stay around for a long time.
Analysis of tap water in Tokyo can be found here for each day starting with March 18. This analysis shows that Tokyo tap water currently contains some radioactive Iodine (I-131), and some Cesium (Cs-137).
Interesting in this context is that according to a WHO report on Japan of March 22 (pdf-file), Japanese health limits for radioactive Iodine are about 10 times lower than global standards, ie if Japanese health limits are exceeded, the levels are still at 10% of global limits (we don’t intend to underestimate this problem however). According to US Ambassador Roos, US Government experts are currently analyzing the Tokyo tap water situation and will report on their findings shortly.
Our short analysis of the radiation data for Tsukuba and Shinjuku:
Gray, Gy, microGray, nanoGray measure the absorption of ionizing radiation. One Gray is the the absorption of one Joule (the unit of energy) by one kilogram of matter, see: http://en.wikipedia.org/wiki/Gray_(unit)
Sv, Sievert, uSievert refers to the impact of radiation on biological tissue, not to the physics of the radiation itself, see: http://en.wikipedia.org/wiki/Sievert
For X-rays and Gamma-rays (which are high-energy X-rays) the units are the same, ie one microGray has the impact of one microSievert, the conversion factor is 1.
You can see that in Tsukuba the radiation impact on humans over the last days has been on the order of 40 – 300 nano-Sieverts/hour, which is oscillating around the natural range of radiation in Austria.
The radiation measurements in Tokyo-Shinjuku showed around 50 nano-Sieverts/hour most of the time, except for spikes above 100 nano-Sieverts/hour.
Click here to see that radiation levels in Austria are in the range of 70 – 200 nano-Gray/hour (corresponding to 70 – 200 nano-Siever/hour for Gamma-Rays).
This means that the radiation levels in Tsukuba are currently similar or a little higher than you would typically experience in higher regions of Austria, while the radiation levels in Tokyo-Shinjuku currently at mid-range for Austria, and have been 30% lower than the lowest radiation levels in Austria for much of the time since the quake. We have made similar comparisons for Italy. The natural background radiation load in Austria and Italy (and other countries) are due to (1) radon gas which emerges from the ground and produced by the decay of natural Uranium, and (2) cosmic radiation from space, which are all exposed to anywhere on earth. Cosmic radiation exposure is higher at high altitudes, since cosmic radiation is screened by the atmosphere.
We conclude that currently radiation levels in the Tokyo region are of similar magnitude as in typical European countries.
Note however, that the radiation levels currently in Tokyo are due to radioactive isotopes which may be inhaled or ingested and remain inside the human body, so there is a difference to natural background radiation. We may analyze this point in future newsletters.
Regarding radiation, please note that radiation is not equal radiation, there are
alpha (= Helium nuclei),
beta (= electrons e.g. inside vacumm TV tubes and old fashioned PC terminals) and
gamma rays (= high energy X-rays),
neutrons, and other types or radiation (e.g. neutrinos).
When people talk about “radiation” from the Nuclear power station, they don’t usually mean the direct alpha, beta, gamma radiation or neutrons, which cannot travel far, but they mean radioactive isotopes which are the product of radioactive decay. The harmful nature of radio-active isotopes depends very much on the type of isotope, and specially also their half-life, and whether they are attached externally to clothing or shoes, or whether they are inhaled or eaten and remain in the body. Some decay very fast, and others live very long. Some, like plutonium are also very poisonous in addition to radioactivity.
The Tsukuba AIST website analyzes the isotopes in detail and lists the occurance as a function of time, as well as the 1/2-life. Shorter 1/2-life (ie I-132: 2.3 hours) mean higher radioactivity, but also mean that such short-lived isotopes also disappear faster.
Further information on radiation levels in Japan, CTBTO data:
It turns out that according to an article in NATURE, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is collecting and transmitting very detailed data on radioactivity and composition of radio-nucleides in and around Japan, but it keeping these data secret.
CTBTO radiation data have now been analyzed by the Austrian Central Agency for Weather and Geodynamics (“Hohe Warte”), and conclude that the release of radioactive isotopes by the Fukushima powerstations corresponds to approximately 20% of the amounts released in the Chernobyl accident. For a short report including animations of the spread of the radioactive plume see here http://www.zamg.ac.at/aktuell/index.php?seite=1&artikel=ZAMG_2011-03-23GMT10:57 .
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