[kamesstory]

Probably had to do with density, if the target is cascading reactions by nuclei to nuclei contact. Solids have a higher chance of contact.

[JoeAltmaier]

Not convinced. The excited atom will travel in a straight line without slowing until it contacts another atom same as in a pellet. The mean free path is longer, but the chance of collision is about the same?

[ncmncm]

Better yet, a wire feed.