Many times I wrote on this blog on radon washout: after a short downpour, we (nearly) always see a visible peak in our gamma radiation, caused by a washout of the daughters of the noble gas radon which is a natural constituent of our atmosphere; to find these comments enter “radon” into the search window on this site or click here , here and here.
A washout means a diminution of the local atmospheric aerosol concentration, and all measurements show that there exist a delay of a few days before recovering. The last few days give us a very good example of two situations: a high precipitation peak followed by a lower one, and vice -versa a small rain peak followed by higher one.
The situation A shows a high rainfall followed after about 6 hours by a smaller one: the gamma-radiation peaks have the same pattern: high, than lower. Situation B is like a mirror image for rain: first small pourdown, than a much higher one. Here the small precipitation peak causes the highest gamma peak: it is a sign of radon washout from a “pristine” atmosphere. 6 hours later we observe a 3-times higher downpour, but the gamma peak is very small: the washout operates on an atmosphere “cleaned” from radioactive aerosol particles (the radon daughters), so there is not much radioactive debris left.
This example shows that it would be a folly to try to find a proportionality between the rain peak and caused gamma rise. The recovery time is a parameter not to ignore. I tried to find a relationship between rain and gamma peaks, if the situation is that of a one-time event, sufficiently far (> 3 days) from a preceding one. There are not many such happenings in a year, and the correlation is poor. Maybe more on this when time permits.
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