There are already commercial oilfield tools that use neutron generators with relatively low power input requirements. I'm not seeing how to make a useful weapon out of something like that, though. What can it do that isn't already done better by normal guns and bombs?

I guess you could use it to attack people inside a building without directly destroying the building, but I would figure that if you got a high enough neutron flux to reliably kill everyone inside the building, you'd also get enough activation radiation to render the building uninhabitable for at least weeks. You might well need fancy decontamination, and possibly to demolish the building and haul away parts of it. Seems easier to just use a bomb.