This in from CNN:
ASHINGTON (CNN) -- New York City will be protected by a ring of devices to detect nuclear or dirty bombs before the end of the year, the Department of Homeland Security said Friday.
A dirty bomb is one that spreads radiation without employing a nuclear explosion.
The Department of Homeland Security hopes the circle of sensors will give warning if a bomb is transported into the city by land.
Most previous detection efforts have focused on preventing a bomb from being smuggled into the city by sea.
Under the "Securing the Cities" initiative, detectors will be placed along highways, at truck stops, in weigh stations and at other sites on the perimeter of New York, as well as locations closer to the city center, an official said. Locations will not be made public "for obvious reasons," the official said.