But it is well possible that some people could still try. The Four Lions, only in the real world.
The other stuff sure, but it takes a truly mind boggling amount of radiation to incapacitate someone (near) instantly. A lot more than that.
100-150 Gy? The only concrete number I found looking around for ‘instant’ was 1000 Gy to likely kill someone within an hour.
It's a fascinating(if very morbid) read if you want to have a look:
https://www-pub.iaea.org/MTCD/publications/PDF/Pub925_web.pd...
The point is, that maybe the terrorists wouldn't be inacapacitated, but they certainly wouldn't be able to ignore the effects for very long if at all.
I think incapacitation is what matters. The human body will fight death for some time, but it won't be able to running around with a heavy backpack of fission material. Various tissues will scream bloody hell almost immediately from being torn apart by the radiation.
Definitely a death sentence either way.
These people are not stupid and would likely know what they are getting in to. I'd be more worried about a single unhinged person, but that's why we have security guards, and the problem would likely solve itself in short order in that case.
https://www-pub.iaea.org/MTCD/publications/PDF/Pub925_web.pd...