That sounds wild. I don’t know where you are but in the USA you could reach out to a university extension program/office and ask them to look into it. It’s bizarre enough to catch their interest and come at no cost to you.
Edit: it really is bizarre because Radon is primarily produced by reactions underground/in the earth and has a relatively short half life (3.5 days). I don’t see how it could be atmospherically sourced without it being a hazard to the whole community, regardless of the bizarre convection currents that bring it into your house. It’s unlikely to be produced in your attic.
If I were you, I’d want to know more and understand how this is all happening lest you raze and rebuild and find you still have a problem.
Radon decays into other longer lived radioactive elements, mostly isotopes of lead, which then condense down as dust and cause more problems than radon itself. So it might happen that these cumulate in the attic if circulation is just right.
Can you share your math? Radon does indeed have extremely nasty decay products, but they are very short lived (which is why they’re so nasty). They’re not accumulating in your attic.
I would suspect fly ash as a possible source if the house ever had a coal-burning furnace. Or maybe someone had a watch-painting operation or mixed radioactive glazes or paints there. Someone with appropriate equipment could do a much better job identifying the source.
I'm leaning towards this. My state has a tremendously high uranium concentration and many uranium mines. It would not surprise me if people were not checking for this in the 60's in concrete mix.
Edit: it really is bizarre because Radon is primarily produced by reactions underground/in the earth and has a relatively short half life (3.5 days). I don’t see how it could be atmospherically sourced without it being a hazard to the whole community, regardless of the bizarre convection currents that bring it into your house. It’s unlikely to be produced in your attic.
If I were you, I’d want to know more and understand how this is all happening lest you raze and rebuild and find you still have a problem.