As you may have seen in the video we posted the other day we were looking into a hotspot in Chiba and some of the contamination there. We have a SAM 940 Radiation Isotope Identifier and some filters for our geiger counters so we’re able to do a little deeper investigation at times.
What we found is that everything is covered with a thin radio-active coating that doesn’t dissolve easily in water or rain (as it has not washed off yet). It doesn’t easily stick to car tires (we measured no increase after one day drive to Koriyama). It is high in alpha and beta besides gamma and sticks to wood, concrete and iron on the surface and is most radioactive on these surfaces. It penetrates soil only on the surface (2-3cm deep) – as it is in the soil you measure lower as the alpha component get shielded. Removal of the top soil reduces radiation by 80% or more. The coating was not deposited by rain – it is only on surfaces that are in open air. E.g. the top of a concrete wall is coated, but the sides have nothing (if it was rain it would have stuck on the sides) or spaces under garden tables are not active, while you would expect rain to have dripped through). It looks like the areas are ‘flashed’ rather than rained/snowed on. When scrubbing with a brush and water on a wooden table we could remove 50%, by using sand paper we got it down to 80% (or more as it measured same as back ground radiation).
In Koriyama we installed a stationary sensor to take measurements in the future as well. Here are some photos from this days events: