As a police pilot, I was asked to participate in a desk top exercise dirty bomb scenario where police helicopters were called to the scene of a small nuclear lap top sized device being detonated in the middle of the city.
Bearing in mind, at the first shout of something like this going off, dozens of police/fire/medical staff would be diverted directly to the scene to attend the injured. The helos would act as comms links / FLIR for heat sources, fire chief taxi's etc etc.
ALL would be contaminated.
Only after all this had happened would someone then realise that a more measured approach would be needed. But of course by then, for those involved it would have been too late.
The general consensus of opinion was that there was no alternative - needs must

I wonder how many 'gold control' supervisors are aware of ESOR's (emergency stand off ranges) and OSOR's (operational)???
When the Berlin Wall came down and the cold war came to an end opening up communist Russia, a part of their military inventory was 21 large lap top hard case sized nuke's. They were designed to be deployed covertly inside a major city centre and detonated by sleepers who would be issued with these weapons. Only 17 have been accounted for to date