From what I’ve learned about Enhanced Radiation weapons (“Neutron Bombs”), they can be built so that a 1-Kt Neutron Bomb explosion produces as much radiation as a normal 10-kt fission bomb.
My question is: Is there an upper size limit to such a weapon? Could you build a neutron bomb in the multimegaton range?
And this is putting aside practical military uses, of course—I’m just talking about the physical and technological possibility.
…I should probably add that, no, I do not plan on trying to build one of the bloddy things, myself.
Best answer I found is:
Due to the rapid attenuation of neutron energy by the atmosphere (it drops by a factor of 10 every 500 m in addition to the effects of spreading) ER weapons are only effective at short ranges, and thus are found in relatively low yields. ER warheads are also designed to minimize the amount of fission energy and blast effect produced relative to the neutron yield. The principal reason for this was to allow their use close to friendly forces.
So I would say no, you couldn’t make a MT range ER bomb because the heat & blast overpower the neutron yield fairly quickly as you escalate in size.