Perhaps A Little Too Late

Nuke detectors to ring New York, official says
"WASHINGTON (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."

Perhaps the following story is why they decided to do this.

ISRAELI EMBASSY IN NYC A RADIATION HOT SPOT
"One alleged radiation hot spot on Manhattan's east side has the potential for becoming a political hot spot: A strong radiation spike from the area of the Israeli Embassy. Officials would not comment on why they thought that particular area allegedly showed such a stunning peak in radiation."