Heavy particles do reach the surface of the earth. The energy is quite high.
Try here: http://www.sciencenews.org/search/se...nd_submit=Find
They ran a recent article on Cosmic Rays and discuss the various particles, energies and the penetration of the earths atmosphere and magnetosphere.
Over time, enough reach the earth to begin fogging film. There is a lengthy thread on this and the amount and type of metal needed to afford protection. I suggest that rather than duplicate this thread here, you look up that old thread.
Lots of good stuff there.