Scientists at Lawrence Livermore National Laboratory in California began testing a device in May that can quickly detect concealed nuclear materials. The invention could plug a gaping hole in American security: the unexamined 6 million ship containers that enter U.S. ports every year.
Physically searching every container would cause shipping to grind to a halt. Today’s scanners—just big X-ray devices—would miss a terrorist’s nuclear bomb or a lump of enriched plutonium if it were shielded in a simple steel box. The Livermore scanner is not so easily fooled. It bombards a suspect cargo with neutrons. If the neutrons hit fissile material, gamma rays are produced that can be instantly picked up by low-cost detectors. The technique, called active neutron interrogation, readily penetrates most shielding, although it does have an Achilles’ heel. “Lead is transparent to neutrons, but hydrocarbons like agricultural products are tougher,” says Dennis Slaughter, one of the scanner’s originators.
Researchers say that the neutrons emitted by the scanner would pose no threat to operators, to cargo, or even to human stowaways. Livermore physicist Adam Bernstein, leader of detector design, says he and his team are close to their goal: detecting as little as a few pounds of plutonium while taking less than a minute to scan each container and creating no more than one in 1,000 false alarms. Bernstein expects to have a full-size prototype ready to start sniffing cargo containers within a couple of years.