Saturday, March 19, 2011

Radioactivity Measurement in Japan

This article was updated to reflect the latest data at 16:29 20/Mar/2011.
With thanks to Pete Warden and Gemma Hobson.

Download: (1.1MB)

Over the weekend I came across some data on levels of radiation in Japan collected by the Japanese government, and helpfully translated into English by volunteers.

Unfortunately the data was also somewhat unhelpfully stuck in PDF format. However between us Gemma Hobson, Pete Warden and I transcribed, mostly by hand, some of the more helpfully formatted files into CSV format (16KB) making it acceptable to Pete's OpenHeatMap service. The map embedded below shows our first results.

Environmental Radioactivity Measurement,
17:00 16th March - 17:00 18th March
For data from the Fukushima site itself see the "Readings at Monitoring Post out of 20 Km Zone of Fukushima" data sets online. Data collection from Mlyagi (Sendai) ceases at 17:00 on the 17th of March and does not resume. Several other smaller duration data drop outs also occur during the monitored period.

As you can see from the visualisation environmental radiational levels change fairly minimally over the time course of the day. Most measurements are steady, and within the historic ranges, except around the troubled Fukushima plant where readings are about double normal levels.

Things become more interesting however when we look at the historic baseline data, the two maps below show the typical range of background environmental radiation in Japan. The first shows typical minimum values, while the second shows typical maximum values, put together they illustrate the observed range for environmental radiation across Japan.

Environmental Radioactivity Measurement,
Typical Minimum

Environmental Radioactivity Measurement,
Typical Maximum

Finally the map embedded below shows the environmental radioactivity measurements with respect to the typical maximum values for that locale. From this visualisation it is evident that the measured values throughout Japan are normal except in the immediate area surrounding the Fukushima reactors where levels are about double normal maximum levels.

Environmental Radioactivity Measurement,
Ratio with respect to typical Maximum Values

However when analysing this data you should bear in mind that the normal environmental range in that area is actually fairly low compared to other areas in Japan. Currently the levels of radiation at the plant boundary are actually still lower than the typical background levels in some other parts of the country. Levels also seem fairly static over time, and do not seem to be increasing as the situation progresses.

Unless the situation significantly worsens, which admittedly is always possible, human habitation in close proximity to the plant will not be affected in the medium term. From talking to people on the ground in Japan, and by looking at the actual measurements across the country, a very different picture seems to be emerging than that reported by the Western media which seems highly skewed, and heavily politicised, by comparison.

I think everyone should take a deep breath, step back, and look at the evidence which is suggesting that this is not another Chernobyl in the making. It's may not even be another Three Mile Island. If the remaining functioning reactor units are decommissioned following this incident it may well have more to do with politics than the science.

Update: A Radiation Dose Chart from the people that brought you The extra dosage you would pick up in a day while in a town near the Fukushima plant is around 3.5 µSv.

Radiation Dose Chart

For comparison a typical daily background dose is around 10 µSv, whilst having a dental X-ray would expose you to an additional 5 µSv. The exposure from a single trans-continental flight from New York to L.A. is of the order of 40 µSv.

Update: This visualization compares the energy mix and number deaths related to each of the main sources of energy worldwide - coal, oil, natural gas, nuclear, hydro and biomass.


  1. If you combine the dose rate information with population density, it's easy to calculate the expected amount of excess deaths, which I'd consider an extremely interesting figure. For low doses and low dose rates, the ICRP estimates one excess death per 20 Sievert of cumulative dose (dose rate x time x population).

  2. Now that's an extremely interesting insight, time to look for population density maps of Japan I think...

  3. Very good! Any progress, yet?

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