This video is a bit long, but it does a great job of showing what can be done with radiation test equipment that most of us can't afford. I really enjoyed the video and found it fascinating, but I'm kind of a geek that way.

https://www.youtube.com/watch?v=tBcKKnBC8Sk

I have spoke with the guy in the video before many times and while most rain has radon fallout in it which is easily detected by our geiger counters, there can easily be other things in the rain. The soil sample project here helps to prove my statement, I have spoken to the owner of this website in great detail too. I have also previously sent my soil for this person to sample. My soil sample results are listed there.

http://www.eagerlabassistants.com/thelab/soilproject.html