Somehow I've overlooked this! It is two weeks old; it is a survey by a team of academics, hosted on Kyoto University's Reactor Research Institute:
Interim Report on Radiation Survey in Iitate Village area conducted on March 28th and 29th
Soil analysis of 8 isotopes:
Note the 137Cs levels on the order of ~1 MBq/m2. This validates previous measurements (see MEXT page for their latest data). MEXT's daily 137Cs readings in this area have been fluctuating by almost two orders of magnitude -- maybe (?) they are measuring in different locations, moving in and out of hot spots (note the units are different here, Bq/kg of soil):
("Island Soil" is a mistake for "Inland Soil"). As a common reference point: the Kyoto University report describes the flowerbed soil sample as averaging 21 kBq/kg 137Cs, and 749 kBq/m2 in terms of area. Maybe this suggests a conversion factor (it's consistent with the earlier media reports).
They also extrapolate back from soil samples to estimate past dose rates -- they infer up to 200 μSv/hour on March 15, or 5 mSv/day, in Magata (where they measured their highest fallout levels). Based on their calculation, the accumulated dose there would be around 50 mSv to date, going up to 95 mSv over 90 days . Note these are outdoor doses (standing above soil); they say being inside a wooden framed house would reduce this by 1/2.
These are the radiation dose equivalents of multiple CT scans. I would definitely not stick around here for extended periods -- and indeed, the Japanese government is planning evacuations for this area.
Note that this survey is geographically limited (map below). The highest dose rates there (colored red) are 18 - 20 μSv/hour; apparently they extend higher further south (into the "stay indoors" zone). As being reported by Kyodo News and others, the NSC estimates the accumulated dose in the 20 - 30 km ring to be <50 mSv, and over 100 mSv in some areas of the (evacuated) 20 km zone.
For comparison, here's the map from the NNSA overflights in approximately the same time period. Not clear to me if "R" is short for "roentgen", or if they've misabbreviated "rem".
Here's an interesting link for studies of caesium by a private german environmental consultancy.
ReplyDeletehttp://www.environmental-studies.de/Radioecology/Rad-E.html
I like the dose rate contours diagram especially. It gives a really strong idea of the variability, from nothing to significant concerns in a few km.
ReplyDeleteGreat addition to the knowledge base out there! I always want to find additional sources of radiation readings.
ReplyDeleteThis is also very good to have the different isotope concentrations. Although I wish we could get some Bq/m^3 readings too. I have a site I want to compare to the atmospheric testing legacy concentrations from.
Yatta! Found my source.
ReplyDeleteYou can make a direct comparison with the historical Cs-137 soil concentration, for example, at Japan's environmental radioactivity website. Fantastic information.
http://www.kankyo-hoshano.go.jp/01/0101flash/01010521.html
Here is their main navigation for the past year's data. I don't see anything on their site that indicates recent measurements pertaining to the current events, although many other similar organizations are doing this.
http://www.kankyo-hoshano.go.jp/study_flash.jsp?runmode=2
So here, you can find the radiation in food, milk, water, soil, ocean water, claims, whatever you want. Amazingly helpful and gives a good backstop for the values we're seeing today.
http://www.kankyo-hoshano.go.jp/study_flash.jsp?runmode=2
In terms of actual numbers, it reports ground activity of Cs-137 maxing out at a few 100 Bq/kg, which is much lower than the numbers we're seeing from this report, but probably came from the dispersion of products of weapons testing all over the world.
Almost certainly Rem and not Roentgen.
ReplyDeleteLook at the highest measured dose rate at the reactor, 100 millirem according to the graph, would be 1 millisievert, which is consistent with JAIF status updates of two weeks ago (right now its 0.5 millisievert, JAIF status update April 16th).
Newer info on cumulative dose for the area, for the year following March 16th. Dose rates up to around 20 millisieverts cumulative for that period. (some areas over 20 millisieverts but assumes people are outside 100% of the time).
ReplyDeletehttp://blog.energy.gov/content/situation-japan/