At a busy border crossing, a truck passing through a radiation scanner sets off an alarm. It could be a nuclear device, but it's far more likely to be kitty litter, ceramic tile or a load of bananas.

"Nuclear materials such as uranium and plutonium are not the only materials that emit radiation," Vayl Oxford, who directs the Homeland Security Department's nuclear office, told a House Appropriations panel Tuesday.

The machines, first installed after the Sept. 11, 2001 terrorist attacks, measure gamma radiation, but cannot distinguish between low levels of gamma rays that occur naturally in innocent materials, and the makings for weapons that terrorists might use.

So the inspectors must pull the truck or container aside for a second inspection with a hand-held scanner, which, at the nation's busiest ports or border crossings, can lead to backed-up lines that anger drivers and slow commerce.

"Naturally occurring radioactive materials ... place an enormous burden on our customs offices, who must respond to all radiation alarms, including those caused by innocent goods," Oxford told the Appropriations subcommittee for homeland security. He explained that distance, dense materials like steel and lead, and the speed at which trucks carrying cargo move — about 5 mph — all affect the scanners' effectiveness.
That's the dilemma of protecting the United States from nuclear terrorism — a trade-off among accuracy, inconvenience and the expense to taxpayers. "The 11 million containers that transit the ports every year (are) an enormous moving haystack that could conceal a deadly needle," said Rep. Hal Rogers, R-Ky.

Government agencies need "to find this proverbial needle in the haystack and prevent it from causing real harm in a way that does not bring the American economic engine to a grinding halt," Rogers said.

About 600 scanners have been installed at ports and border crossings around the U.S. Government officials are working with several companies to develop new nuclear detectors that won't waste time and that can actually differentiate the potassium in a banana from that in highly enriched uranium.

Tests being conducted in Nevada this month pit new detectors against the older ones, to determine whether the higher accuracy claimed by the makers of the new machines is enough to justify their higher cost — around $377,000 each, more than six times the cost of the older models.

Later this spring, the new machines will undergo a real-world test on the New York waterfront so Customs officers can judge for themselves if they're an improvement. They're also to be used in similar tests along roads leading to the city as part of an effort to set up a protective perimeter starting in 2008.

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