re: I wonder if they looked at the Earth's atmosphere for Gamma rays.
Lately I have been agreeing with quite a bit of what you are saying but there are some things that I disagree with.
You said:
You seem to be suggesting that nuclear detonations and reactors have put measurable amounts of radioactive waste in the upper atmosphere. While this might be possible after a recent nuclear wepon detonation, the chances diminish over time as those heavier particles would wash down with the rains and simply could not sustain aloft over a period of years or even months.
I agree that rain and other factors can reduce the quantity of radioactive waste from the atmosphere, but it depends on how high and what velocity the particles have.
Suppose that the particles are above the <a href="http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html>troposphere and have high enough speed, then they could go into orbit around the Earth or even escape from the gravitational field.
There have been many explosions in or near space.
There have also beenlot of accidents that are radiation related.
How can you be sure that remnants of these explosions are not in the atmosphere anymore?