"We'll have people walking around with various detectors and devices.
They'll come up to people, they'll look for anything unusual," said Tom D'Agostino of the National Nuclear Security Administration.
But, the nuke swat teams are only part of the defense against improvised nuclear weapons and dirty bombs.
Nuclear scientists say the closer we are to the ground, the closer we are to the radiation and the better we can see it.
From the air Department of Energy scientists can also zero in on nuclear threats. We rode along on this training flight as undercover scientists searched for "planted" radioactive cesium.
We can't show you the cesium but a spike on a radiation monitor directed the chopper right to the target.
"What that says to me is that I have a radioactive isotope emitting energy, this is more than likely where the source is," a technician said.
In big cities, like Washington, nukes and dirty bombs could be difficult to detect. "Naturally-occurring" radiation is everywhere given off by the granite from office buildings and the tombstones at Arlington National Cemetery. So, scientists are also working to chart existing radiation sources.
"It's important to establish a baseline of what radiation is there already so in case there is an incident we won't be led astray by anomalies" said a nuclear scientist.
The nation's top two terror targets: Washington and New York are already "mapped." Chicago is next.
Skeptics downplay the risk of terrorist nukes, but the consequences of an attack are unthinkable.
So these radiation-hunters warn: we can't afford to stop looking for the nuclear threat.