I found out that City Hall will let you test your garden soil for radiation. So I did.
491.3 Becquerels per kilogram.
A quick refresher of terms:
Becquerels tell us the rate at which radiation is being released.
Microsieverts estimate how much damage is being done by radiation around you. The city measured our general neighborhood at 0.23 microsieverts/hour. If you multiply that number by 8766 (24*365.25 the number of hours per year) you get 2016 microsieverts, or 2 milisieverts per year of exposure. That is about the world average according to Wikipedia.
The University of Tsukuba (Japan's MIT) has a very easy to read primer on radiation.
Assuming that it follows standard half life formulas, I made a spreadsheet to determine how much radioactivity I can expect to see as time progresses. (I love making spreadsheets)
(Please note, I am not a scientist, my calculations and theories could be way off.)
|Projected Bq/Kg 2012-2020|
|Projected Bq/Kg 2020-2100|
As you can see from the report, about one third of the radioactive contamination is from Cs-134- with a half life of 2 years. So in 8 years, after four half lives that will be below the ability of City Hall's machine to detect. Which leaves the Cs-137, which has a half life of 30 years. This beast will take some time to reduce. We are looking at 120 years for four half-lives, which would bring it to below my totally arbitrary threshold of 20 Bq/Kg.
Of course, what do the numbers mean? What is a "safe" level of radioactive contamination? The new Japanese government standards for agricultural products is less than 100 Bq/Kg.
They have observed as a very broad rule, about 1% of the Cesium is absorbed into plants. So following that rule, my vegetables should have about 5 Bq/Kg. I do plan on testing the first harvest all of the crops before they reach the table.
On another note, I plan to try removing some of the Cesium with sunflower roots. The stalks, leaves, and flowers absorb very little, but the roots are said to accumulate Cesium like crazy.
I plan to grow the sunflowers, pull them up by the roots, and burn the roots to reduce the mass and concentrate it. Then I will send the ashes to TEPCO with a note- "I think you dropped this, thought you might want it back."
(Nuclear Power- Only 100 accidents since 1952...)