Google Maps Visualization of Fukushima Dosage Data

Note that the map below and the data it contains are for demonstration purposes only: it does not display the latest readings, and is not intended to be used for decision-making.

Based on data released on 28 March 2011 by MEXT showing cumulative and average hourly radiation dose at 10 monitoring posts around Fukushima 1 NPP.

The circles in the map are centred on the approximate location of the monitoring posts. The sizes of the circles represent the relative magnitude of the cumulative doses recorded at those posts. The colour of each circle represents the average hourly dose, with red indicating an average dose of 20 µSv/hr or more, amber an average dose of between 10 and 20 µSv/hr, and green an average dose of less than 10 µSv/hr.

Note that the source data is based on readings at the various posts over durations ranging from 1 day to 4 days, and hence the data and the representation of it below (especially the cumulative dose) are not directly comparable.

Japan 2011 Twitter Feeds

Notes on Radiation Dosage and Visualization of Radiation Data

Notes from Bruce Bennett, RAND provided to Austin Tate on 27-Mar-2011:

Personally, I like the map produced at:

•  http://www.nytimes.com/imagepages/2011/03/19/world/19radiation_g.html?ref=asia

To avoid confusion, the key units of radiation are (you may already know this):

Exposure:
   1 Gray (Gy) = 100 rad = 1000 mGy; 1 mGy = 100 mrad = 1000 µGy 

   1 µGy= 100 µrad = 1000 nGy

Dosage
   1 Sievert (Sv) = 100 rem = 1000 mSv; 1 mSv = 100 mrem = 1000 µSv
   1 µSv = 100 µrem

The prefix “m” is for milli and “µ” is for micro and “n” is for nano.  Be careful to use “µ” and not “m”.  

While it is a huge approximation, it is usually assumed that 1 Gy = 1 Sv, and that 1 rad = 1 rem.

It is usually assumed that a dose of around 450 rem (4.5 Sv) (some say 300-350 rem) has a 50% chance of killing people, and doses of 600 rem or higher are usually not treatable and will kill most people.  A dose of 100 rem (1 Sv) has a 50% chance of causing serious radiation sickness (vomiting, ...).  These are short-term effects.  To avoid getting anything near these numbers, nuclear plant workers are usually limited to doses of 5 rem per year, and the public exposure from nuclear radiation is limited to 100 mrem per year (this is so low because young children and fetuses are thought to be about 10 times more vulnerable to radiation than adults).  It is usually assumed that short-term radiation sickness symptoms will occur at doses of 30 to 50 rem, explaining the decision of the Japanese government to allow workers at the plant to receive doses up to 25 rem.  It is, nevertheless, not appropriate to let people cross the nuclear radiation limits unless there is a very good reason—in the United States, such a thing would be a liability nightmare.

Long-term nuclear effects (e.g., thyroid cancer) can occur at lower dosages.  This helps explain the concern for Iodine-131, which tends to accumulate in the thyroid.

In most of Japan, the background radiation dose is about 0.05 µSv/hr, which over a year would accumulate to ~500 µSv, or 50 mrem (various other forms of radiation would raise the annual dose to about 100-400 mrem).  But some places in Japan have twice as much background radiation.
  
Most of the presentations of exposure or dosage data are in terms of hourly exposures or dosages.  But the key is the cumulative dose or exposure.  To get this, we need the hourly dose over time.  For example:

 This leads to cumulative numbers like:

So this area was half-way to the 100 mrem limit by March 25.

The key would thus be to show cumulative doses and projections.  There are several problems in this:

1. Most of the data does not begin until March 15, and yet there was serious exposure at least as early as March 14.
2.  As these charts show, a new spike in radiation could accelerate the rate of dose increase, but that in theory should be a function of wind direction.

 The problem we have now is that we don’t have wind direction data immediately available for Japan from March 12 on—I am sure it is out there, I just have not been able to find it.  Ideally, the data we need is like that displayed at:

• http://www.windfinder.com/forecasts/wind_weather_forecast_google_map.htm?lat=37.42&lng=141.03&z=9&offset=3&s=37.42,141.03

I am particularly interested in when the spikes occurred on March 14, 15, 16, and 21.If we only have winds over the plant, we don’t know where the radiation went downwind, whereas this information helps.  The key is determining how the hot spots developed around the plant—were they a function of the major winds or something else?

Notes from Bruce Bennett, RAND provided to Austin Tate on 28-Mar-2011:

MEXT has now posted cumulative doses for 10 locations over 3-5 days.  These numbers miss the hottest periods for these locations, but still show:

These doses are in µSv (middle number) and µ Sv/hr (last number in parentheses—current average dose).  So for monitor point 32, the dose of 4,813 µSv = 481 mrem, which is almost 5 times the allowable population dose.  And this cumulative does not include the hottest period, starting back on March 17.  Hopefully, people have been evacuated from this area!

This said, it is important to go back and calculate the cumulative doses, even if these can only be approximately determined (because the data is only presented twice each day, though in many cases multiple hourly readings are given).  Thus, for point 32, the data on hourly dose is:

The cumulative dose (based on averaging between doses, which given the dose pattern generally seems reasonable) is:

 There was some dose, as well, before March 16, but I don’t see readings posted before that date, and they were likely small.  On the 16th, reactor 3 had white smoke and high radiation arising about 0830, and continuing into the afternoon or so.  Based upon the other radiation readings, my guess is that there was a wind from the southeast some time between the late afternoon of the 16th and the morning of the 17th.  The slow decay of this radiation suggests that it contained a lot of iodine and cesium.  While the cumulative picture shows 4,813 µSv = 481 mrem from some time on the 23rd to some time on the 27th, the actual total by the 28th is 5 times as much.