A sister company to a company I used to work for tested basements for radon. Levels were high where there was granite. They had to use long exposure test kits (no clue what they were or how they worked) because meter readings were artificially high (no clue why).

I did QA and safety, rad safety included, for an oil field research project where a lot of naturally occurring radioactive material (NORM) was brought up from the deep via drilling. The uranium daughters were somehow “bound” with barium. I don’t know if that radioactivity can be close to the surface in certain parts of the world, but maybe it can.

I don’t recall the correct vocabulary for the blah blah blah above, and I don’t remember if I even ever figured out the barium thing in the first place. I worked for a bunch of engineers and physicists who wanted me to stay quiet in my corner, and just do the paperwork needed for reporting to the funding agency. I at least have given you some words to Google.