This question about nuclear reactor shielding got me wondering, what forms of radiation are the hardest to shield? I suppose Neutrinos will have to be excluded since they're the obvious winner.
So assuming an equal kinetic energy, what's the hardest radiation to shield? I think I've read Muons penetrate to much greater depths in accelerators but surely there are other things that are hard to attenuate.
I'm not really looking for a list so much as an explanation for what makes a particular particle (or groups of particles in the case of Alpha particles) difficult to shield.