I'm working on a head project, and I wanted to keep this faction in question as close to hard sci fi as possible, and instead of the usual sci fi military tropes, they will basically try and nuke the shit out of anyone who tries to land on their planets. No plasma, no lasers, no honor duels with holtzman shields and chainswords, just fission bombs until the problem goes away.

Now this faction is composed to professional terraformers, so cleaning up the radiation afterwards isn't a huge deal. But given their views on using nukes, is there a way to precisely align nuclear material so it becomes 'superclean' as in producing almost no fallout either by using lager amounts of the material directly (I think right now a nuclear bomb only uses 2% of the material and the rest is blown off) or is better at converting into gramma radiation so it;s incredibly lethal at time of contact but quickly goes to safe levels.

Is such a thing possible, even in theory? And if so, what might be the limitations? C ause I was thinking they actually use Davy Crocketts (20 tons of TNT) as skirmishing weapons, literally launched out of the beds of local police trucks like the new VAMPIRE missile systems.