User blog comment:PerhapsTheOtherOne/Speculative Spitballing: Goliath/@comment-25555436-20150608190144/@comment-7622429-20150608200635

Wrong on your part, again. In pretty much every Godzilla film, anytime militaries fire upon the creatures, they either ignore it, or simply swat/blast the buggers. You can't say they're doing damage because we see no visual indication of such sort. There's a reason daikaiju are the Trope-namer of the "Giant Equals Invincible" trope. Countless sources have gone on to state that, indeed, these creatures are generally immune to firearms and artillery, etc. You can visually see that no damage is done, via their mannerisms or the look of the suits themselves.

Also, a nuclear bomb isn't just radiation. It's nuclear fission that literally rips apart atoms in the immediate vicinity, plus the thermal and kinetic force. Radiation doesn't happen until at least a few minutes after the initial explosion.