Why is it so significant? Because the people in question were working with something much like the internals of a nuclear weapon. Yet but for the criticality accident they caused through carelessness, the radiation dose rates would have been nominal. Moral? Nuclear bombs (as opposed to "dirty bombs") aren't as radioactive as you might think.
Which means that installing radiation detectors in public places would probably be good for little besides PR:
Finally, NEST operations would go into effect if a credible threat of a dirty bomb or a full-fledged nuclear weapon were to manifest itself. If the information available would allow the U.S. teams to locate the city affected, hundreds of team members would fan out along a matrix of the threat region to detect the bomb. Carrying gamma- and neutron-detectors inside carrying cases to preserve secrecy, the NEST members would cover the suspect area on foot, in vans and helicopters — going in and out of buildings hoping to register the tell-tale signals of a hidden bomb. Once found, the bomb is x-rayed, "sniffed" and otherwise analyzed to determine its characteristics.US commercial nuclear power plants don't figure into scenarios for nuclear weapons. There's nothing onsite that you can make into a nuclear bomb - the enrichment is too low, and there's no apparatus for enriching it onsite. There's stuff that's good for dirty bombs, but likely it's so dirty that the creeps stealing it would be incapacitated themselves before they got it anywhere where it could cause much harm.
Obviously, intelligence that helps localize the bomb is the main key to success. Just as obviously, intelligence of such quality is seldom available — as proven on Sept. 11. Such a search could be truly looking for a needle in a haystack, as detection normally would succeed only if the detectors come within a few feet or so of the hidden bomb.
Maybe something like this will help with detection.
At any rate, nuclear terror threats are old news:
...it has been reported that between 1975 and 1981 NEST personnel were sent to investigate threats in Boston, Los Angeles, Spokane, Pittsburgh, New York, Sacramento, Tennessee, and Reno...