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Bbrhuft t1_jcajnfa wrote

FYI. have a radium dial compass sealed inside an air tight jar, safely stored in an unoccupied room. It's highly radioactive, back then Zinc sulfide phosphor wasn't particularly sensitive so they compensated by adding extra radium.

Anyway, the interior of the jar gets coated with radon daughter plate out:

This is the decay I measured, due to Bismuth-214 and Lead-214 decay.

Anyways, the contamination stubbornly adhers to the glass. I tried rubbing it off with tissues, dampened with water and alcohol. I estimate I can remove about 25% of the contamination, by measuring the radioactivity on the tissue, most remains stuck to the glass.

Radon Plate Out occurs because the decay products (218Po, 214Pb and 214Bi) are electrically charged, they are attracted to dust and surfaces that are slightly charged.


mergelong t1_jcapyht wrote

I find that pretty interesting, but I imagine that especially the upper atmosphere, with high levels of ionizing radiation and radicals floating around, doesn't resemble inside of a jar, not to mention the distance the daughter nuclides must travel before deposition is vastly increased for atmospheric radon decay products.


Bbrhuft t1_jcat9ql wrote

Radon Daughters stick to dust at ground level and that dust is carried into the higher atmosphere by rising air currents, they can rain out when there's heavy rain, thunderstorms particularly, a phenomena called Radon Washout.

It was discovered by accident in the 1960s. A nuclear worker walked though puddles in a car park on the way to work, and he set off the alarms as he arrived, since that's backwards they were intrigued, and they discovered that atmospheric dust is coated with radon daughters which can get concentrated in electrically charged thunderstorms, and rain out as Radon Washout.

Radon Washout can sometimes be intensely radioactive, and there's a paper that estimated that a few percent of skin cancers might be linked to Radon Washout, beta radiation from Lead-214 and Bismuth-214 decay is able to penetrate the outer layers of the skin and deposit a radiation dose to living skin cells, a risk increased for people who work outdoors. This might be speculative, nevertheless, it illustrates just how radioactive rain can be sometimes be when weather conditions are just right.

I measured it myself a few times. Got readings up to 2 microsieverts per hour, nothing spectacular.

Styro, B.I. and Stelingis, K.I., 1978. On the value of flow of long-lived radon-222 decay products into atmosphere with the dust of natural and anthropogenic origin. In Chemical and radioactive pollution of the atmosphere and hydrosphere. V. 4.

Edit: Also, >90% of indoor radon daughters are bound to dust, very little is unbound, free floating.


drsoftware t1_jcb2kj7 wrote

Another writer responded with mean free path and velocity for particles. Given that dust, that is other larger masses than individual oxygen atoms, will the electrically charge particle be much more likely to first bound with oxygen and then with dust?