Gamma Ray Penetration
If gamma rays can penetrate everything, then how can the
atmosphere stop gamma and x-rays?
You have started with a false assumption that "gamma rays can penetrate
everything". That is not the case. True, they are very penetrating, but they
do interact with matter, and their "tracks" can be observed.
Gamma rays don't penetrate materials infinitely, they just penetrate a lot
more deeply into materials (than, for example, alpha or beta particles)
before they're absorbed.
Hope this helps,
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Update: June 2012