With nearly 400 border crossings and more than 20 major seaports, the country is vulnerable to potential terrorists trying to smuggle in nuclear material. It's a possibility for which government officials know they must prepare.
"As unfortunate as the recent events have been down in Louisiana, a nuclear attack against a metropolitan area would be orders of magnitude worse," said Dr. Vayl Oxford, director of the Domestic Nuclear Detection Office. "And we have to figure out how to aggressively keep that from happening."
For Oxford, a big part of keeping it from happening means having the best technology available.
For years, America's front line of defense has been nothing more than sophisticated Geiger counters. But the detection devices do a poor job of discriminating between naturally occurring radiation -- which can be found in everything from kitty litter to fertilizer -- and highly enriched uranium -- a dangerous, weapons-grade material.
The uranium, and other material which can be used to make a "dirty bomb," is usually shielded by lead, thus giving off little radiation.
"They could bring the weapon today inside a cargo container that comes to one of our ports, and the technologies that we have deployed would have a low chance of finding it," said Graham Allison, director of Harvard University's Belfer Center for Science and International Affairs.
Now, scientists at government labs and private companies are working together to develop next-generation detection equipment called "portal technology."
The new devices detect even the weakest radiation and then use sophisticated computer software to specifically identify the source. It should cut down on false alarms and therefore improve security without disrupting commerce.
In an exclusive demonstration for ABC News at Sandia National Laboratories, a truck drove between two detectors and set off an alarm. In less than one second, computers told operators that the truck was carrying only low-level, naturally-occurring radiation from fertilizer.
But can the equipment detect a dirty bomb shielded inside a lead container?
"Yes, some of the gamma rays still come through the shielding," said Gene Kallenbach, countermeasures project leader. "Now the important part is the software has to be able to sort of unfold that signature."
And it does. Now, the challenge is to take these prototypes and manufacture hundreds of detection devices -- along with the "smart" software -- that can be loaded into a simple laptop computer and easily operated by security personnel.
"They don't care about the scientific mumbo jumbo," said Dean Mitchell, a technical engineer at Sandia. "What they want to see is which vehicle caused the alarm and what is the text analysis. "
The technology has also been mounted in golf cart-like vehicles and Jeeps, which appeal to port operators because of their mobility and ease of operation.
So far, the new dirty bomb detection equipment has been installed at only one major East Coast seaport.
"We have a deployment plan to get detectors in place within the next several years to cover in our mind what is about 371 ports of entry that cover the land borders and seaports," Vayl said.
The question, security analysts say, is whether they will be installed in time.
ABC News' Bill Redeker filed this report for "World News Tonight."