Well God isn't going to miraculously have a nuke appear for some nutcase religious freak terrorist to explode. God, just like everyone else, has to abide by the laws of nuclear physics. Anything else is Tom Clancy & Hollywood.
There are basic facts of nuclear science which must be adherred to. Now I made various comments on a another thread some time ago on this topic & they're as relevant then as now. Contrary to popular myth, nukes are about the hardest thing on Earth to build. Not only do you need U-235 or Platonium, which needs to be weapons grade to top it off (in other words over 90% pure), you also need to figure out which way you're going to go in nuke design. So you have your pick - U-235 or Platonium. I'm not even going to talk about a terrorist H-Bomb as it's even far beyond the abilities of even several nuclear capable states to build successfully.
Now the U-235 bomb requires more than merely slaming together two pieces of weapons grade U-235. This first part will be impossible anyway for terrorists to get because it's very rare & only a few countries have it. Using reactor grade U-235 isn't going to give you critical mass let alone a dangerous reaction, as the common reactor grade U-235 is only about 30% pure. Considering we're talking about 5kg of U-235, I'd highly doubt that a runaway reaction will even take place. But there's much more to the U-235 bomb than just the U-235. You need two isotops of lithium which are only used for one thing - that's getting the critical mass to take place for the explosion. Well if you think getting U-235 difficult to get there's no chance you'll get these isotops.
The Plutonium bomb can be easier, as you don't need the two isotops of lithium, but then again you still need 5kg of weapons grade plutonmium. Guess what? That's even harder to get than weapons grade U-235. So you're stuck even before you start. And this is besides the fact that you need the all important atomic triggers in order to get the exact imposion that is required in order to have the Plutonium go critical mass & thus the explosion. Well these atomic triggers are used for basically one thing - a Plutonium bomb. Like everything else required for a nuke, they don't drop off the back of a truck, but a highly guarded. In other words, the terrorists won't be getting the triggers either.
The only real choice for a terrorist is to steal a nuke. Forget it. The Bomb business is the most dangerous one on planet Earth & is taken deadly seriously. Anyone trying to steal one will, either die in the attempt, or will be hunted down & killed even if, and it's one huge IF, they manage to steal one. And this is besides the point that everyone's Bombs have some sort of security system on them requiring the necessary code(s). Believe me, all this has been gone into by the powers that be & every angle has been covered.
The only realistic option for terrorists is the dirty bomb. That is they use industrial nuclear waste & explode it using a conventional device, on top of a tall building, where the wind carries the nuclear waste as fallout over a city. The only hassle is, thanks to numberous studies, it has been found that this idea not very effective. It's been calculated that somewhere between 1 000 - 10 000 people might get cancer as a result of such a dirty bomb, but this is in the long term casuality region & it doesn't have the desired effect of a high number of deaths. Having said that, there would be the perceived threat, now obviously known by the public, that they are under nuclear attack. And it's this perceived threat, which will have a much more impact upon countries, than the actual threat from terrorist nuclear attack. But, in reality, little has changed other than the terrorists have tried a different apporach. In the aftermath, however, of such an attack by a dirty bomb, you can expect that all nuclear waste, in future, would be guarded as highly as if they were Bombs.