Some obvious MISTAKES

As regards the bomb, the primary is a plutonium bomb, probably only 10 kilotonnes or so ("only"). Since the SS-18 warheads are thermonuclear bombs, they have a jacket of lithium deuteride that boosts the complete device up to 500 kt. If all you want to do is blow up the UN, then a 10 kt device will do the job adequately.

Now, the way the putonium bomb works is that the explosives surrounding the core squeeze the plutonium, increasing the density to the criticality point where the chain reaction causes a nuclear explosion. The timing and configuration of the explosive lenses is critical. Get the timing off by microseconds, or the angle of the lens wrong by milliradians and the plutonium gets squeezeed unevenly and the thing won't blow. Get it wrong badly enough, and the plutonium won't even get hot enough to melt. So what Kidman's character is trying to do is disable one of the lenses or at least knock it off alignment so that when the timer reached zero, the explosives went off, but the plutonium didn't get critical. It's possible that she disabled the lens completely and the plutonium just got hammered into an odd shape by the pressure of the explosion, without even melting. So, no nuclear explosion, no radiation pulse to speak of, no vapourised plutonium, no plutonium dust.

If you want to make a dirty bomb, you need to do more than just strap radioisotopes to some HE. If the isotopes are metal, then the explosion will just knock some radioactive metal bits around, easy to trace and easy to remove. Only amateur terrorists plan to make a dirty bomb this way. If all you've got is ordinary HE, then you'll cause more damage and misery with ordinary ball-bearings and nails.

As to your other points:

1. SNAFU. Somebody decided that, obviously, the lock-down didn't apply to diplomats. After all, what would diplomats be doing with a bomb?

2. Ordinary flight, wasn't it? One of the stopped ones, maybe? Obviously, you can't stop flights in the middle of the Atlantic, they have to land somewhere.

3. Dramatic necessity. The viewpoint character has to do the job, otherwise the film loses focus. In the real world, the job would get done by someone else, so it's not a great sacrifice to realism for Cloony and Kidman to do it. On the other hand, time is short, so if Clooney and Kidman are the guys with the knowledge then they should be at the sharp end so they can get any intel they need without having to spend time briefing and debriefing others.

4. There was a perimeter, but Gavrik (sp?) slipped out before it was established. Rather than show all that, the director just bypassed that entire uninteresting scene.

5. The sniper *beep* up. People do that, sometimes at the most inconvenient times. Often, in fact, that's what makes them *beep* He didn't _want_ his bullet to perforate the little girl. I can sympathise.

6. No, maybe not. They were just told to stop anyone with a backpack and search them. This was way before 9/11, remember, back when the US didn't take this stuff seriously. And they'd already stopped a dozen people before coming to Gavrik without finding anything, so they'd probably lost all enthusiasm for this game.

7. Clooney heard someone sneaking up behind him and reacted to that, as a soldier would. At that point, Gavrik might have had his hand on the deadman switch, whereas he probably wouldn't have when he was just walking down the street. And maybe it's just as difficult for Clooney's character to shoot a man in cold blood as it is for the sniper to shoot a little girl.