Neutrons are some of the smallest atomic particles and are able to pass through all solid matter. Unlike other forms of radiation, only a material rich in hydrogen is able to slow the particles enough to provide any sort of protection. Water is best, but any material that has water in it can be effective.

So yeah, what Deuce said, except more sciency. You can blame the fact that General Atomics is pretty much down the street from me.

@compasseagle89: Fusion reactions are possible and sustainable (barely) in TOKOMAK facilites. The only reason we aren’t using them for producing energy is that the total energy input far exceeds the current energy output.

@GorillaMunch: Yeah, because Chernobyl and all their other poorly shielded reactor facilities are so much further away from major population centers…