Samuel -

Not being able to read Japanese all I could work with were the numbers. I dropped several of them into the equation for calculating dose rates from a plane source assuming the measured levels were due to radioactive particulate released from the plants and were evenly distributed on the ground.

The dose rate from a plane source is calculated as follows:

1. From on-contact to .1r, the dose rate is as measured on-contact. (r = the radius of the plane source)

2. From .1r to .7r, the dose rate = .333 x the on-contact dose rate

3. Beyond .7r, the dose rate is caclulated using the point source equation (inverse square function)

I assumed the radius of the plane source to be 10 meters. I also assumed the 1 cm dose rate measurements to be an on-contact reading (close enough for the calculation) For an on-contact reading of 5.3 microSieverts/hr (taken from sample point 8 in your first link), the estimated dose rate at .1r, or 1 meter should be 5.3 microSieverts/hr. It was measured at 3.2 microSieverts/hr. Since the 1 meter dose rate was less, that tells me either the assumed radius was too large and it was less of a plane source and more a point source, or it was measuring background.

If you change the radius to 2 meters, the numbers should work out as follows:

From on contact to 20 cm (.1r), the dose rate is 5.3 microSieverts/hr

From 20 cm to 140 cm the dose rate would drop off to .333(5.3) = 1.77 microSieverts/hr

Again, since the dose rate measured at 1 meter was 3.2, nearly twice what it should be, that tells me that the readings are measuring very close to background levels since they don't change with distance as expected. If you look at the other readings at other sample points, the 1 cm and 1 meter readings are even closer.

On pages 14 and 15 of the survey results in the first link provided, the readings at sample points 25, 26, 27 and 30 have readings significantly highers than on any of the other pages. These values follow the plane source calculation - I would not let my kids play there. I would encourage Harry Reid and John Boehner to play there.

What we would need to see are dose rate measurements taken before the accident to see what the normal background levels were. Even then, using the numbers provided and the apparent fact that they don't fall off with distance as expected tells me that the measurements are background levels.

Subject to isotopic analysis, given these numbers, with the above noted exception, I would let my kids play on the playground.

Here are files containing measured amounts of radiation for about a hundred school playgrounds in the prefecture of Fukushima per file:

http://www.pref.fukushima.jp/j/schoolmonita0405.pdf

http://www.pref.fukushima.jp/j/schoolmonita040602.pdf

http://www.pref.fukushima.jp/j/schoolmonita0407.pdf

As one can easily note, the radiation levels are consistently higher at 1 cm than at 1 m above ground. They are not taking samples to figure out what's actually in the dirt (anyone care to speculate?), but the question remains: Would you let your kids play there?

Samuel