Arg. Had a moderately long, not quite Randall Munroe worthy explanation written up but it got lost by accident. Sorry. :( In a nutshell, that'll never happen.

Arg. Had a moderately long, not quite Randall Munroe worthy explanation written up but it got lost by accident. Sorry. :( In a nutshell, that'll never happen. You'd have to be the unluckiest astronaut to ever live. These particles reach Earth at a rate less than 1 per century per square kilometer. So you'd have to hang out in space for like a hundred million years... The original particle never reaches the ground. It gets annihilated in a collision some tens of kilometers up in the atmosphere. If you were hit, I'm not sure the cascade would do significant damage before it exited your body on the other side.