What do bananas, smoke alarms, toilets and large granite buildings have in common? They're all sufficiently radioactive to set off detectors. Efforts since 9/11 to prevent the detonation of a dirty bomb—an explosive device designed to spread lethal radiation as well as panic—are plagued by the risk of false alarms. When 350,000 or so radiation-therapy patients in the United States and Europe can cause detectors to light up if they get close enough, you know a solution isn't going to be easy to find.
And it hasn't been. The current state of the art, "spectroscopic" detectors, can distinguish between the harmless beta rays given off by the potassium-40 in bananas and the very dangerous gamma rays from uranium and plutonium, which are used to produce nuclear fuel and nuclear weapons. But they're expensive. In the run-up to the Olympics, China bought many detectors, at $27,000 each, from the Beijing firm RAE-KLH Technologies to check people and vehicles entering the Olympic Village, airports and other venues. The detectors, too, are limited because they can work only at choke points, such as entrances to buildings or compounds, resembling the walk-through metal-detector gates used at airports. By contrast, to search for dirty-bomb radiation at large calls for cheaper electronics technologies, which are just now starting to become available.
One new technology uses surveillance cameras with sensors tuned to radiation. In June, Splinternet Holdings, a security firm in Norwalk, Conn., began "wrapping" buildings with radiation-detecting cameras that cost less than half as much as the Chinese model. The detectors differentiate between benign and dangerous radiation, a big help for organizations such as hospitals that are trying to prevent the theft of radioactive material.
Some researchers are incorporating everything needed to detect radiation onto computer chips, which are smaller and more reliable than sophisticated spectroscopic radiation detectors. The security firm eV Products in Saxonburg, Pa., is already marketing a chip that's only a cubic centimeter in size. In large volumes, the company says, the device would cost less than $50; eV Products has provided several hundred to classified U.S. government programs. Rick Smith, head of sales, says his government clients are handicapped by the desire to develop overly complex systems able to identify biological and chemical threats as well. Such requirements would add years of research, and result in larger, more-expensive sensors.
Technologists at Purdue University in Indiana are determined to avoid that pitfall. "We have to fight this American knee-jerk toward the highest tech," says Andrew Longman, a project leader. The Purdue team is designing a detection system that's so small it could fit into cell phones. The project, known as Distributed Nuclear Detection by Ubiquitous Cell Phone, would help locate dirty bombs or nuclear weapons by "triangulating" the source of radiation when people carrying mobile phones pass by. (The greater the number of equipped cell phones, the greater the precision: phones closest to radioactive material would register stronger signals.) The Purdue project and others like it represent a "major shift" in combating radiation terrorism, says Rita Colwell, a former director of the National Science Foundation and now a professor at the University of Maryland.
The most effective system, says Longman, will be as inexpensive as possible, so hundreds of thousands or millions will carry sensors inside their cell phones. The Purdue team is lobbying Congress to require cell-phone users and telecoms, which will have to collect the data, to participate. Yet legislation mandating participation may not be necessary. Government agencies could simply pay mobile owners and telecoms that agree to opt in. Deploying detectors in mobile phones is promising, experts say, because the greatest concentration will be in cities, precisely where dirty bombers are most likely to strike.
The race to deploy a mobile-detection system is on. The technology could soon cost less than $100 per cell phone, says John Peeters, CEO of Gentag, a Washington, D.C.-based company developing a system similar to the Purdue model. Simon Labov, an engineer at the Lawrence Livermore National Laboratory in northern California, is working on a device, called RadNet, which he thinks will be ready to test in 18 months.
Funding at U.S. government labs and agencies has slowed, however, perhaps because of uncertainty over the budget priorities of the next administration. Even so, the Department of Homeland Security has said it will support the most promising system. This could include compensation for participating citizens, who will have to carry slightly larger cell phones equipped with radiation detectors. While cash might entice some, the designers of mobile-phone detection systems note that many people would likely opt in simply to play a new and surprising role in protecting national security.