What do bananas, smoke alarms, toilets and large granite buildings have in common? Like many objects, they're sufficiently radioactive to set off radiation detectors. Efforts since 9/11 to prevent the detonation of a dirty bomb—an explosive device designed to spread harmful or lethal radiation, as well as panic— are plagued by the risk of false alarms, known as false positives. When 350,000 or so radiation-therapy patients in Europe and the United States can conceivably cause detectors to light up (if they get close enough), you know a solution is not 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 given off by 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 of the detectors, at $27,000 apiece, from the Beijing firm RAE-KLH Technologies to check people and vehicles entering the Olympic Village, airports and other venues. Such detectors are limited in that they can work only at choke points such as entrances to buildings or compounds: they resemble the large walk-through metal-detector gates used at airports. To search for dirty-bomb radiation at large calls for cheaper electronics technologies, which are 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, Connecticut, began "wrapping" buildings with radiation-detecting cameras that cost less than half as much as the RAE Portal. The detectors differentiate between benign and dangerous radiation as people enter and leave the building, a big help for organizations such as hospitals and research labs that are trying to prevent the theft of radioactive material.
Some researchers are incorporating everything needed to detect radiation on to computer chips, which are smaller and more reliable than sophisticated spectroscopic radiation detectors that have moving parts. The security firm eV Products in Saxonburg, Pennsylvania, is already marketing a chip that's a cubic centimeter in size. In large volumes, the company says, the device would cost less than $50 each. eV Products has provided batch quantities of 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 West Lafayette, 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 will 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, who will have to collect the data, to participate. Yet legislation mandating participation would 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. "You meet the enemy at his point of desire," and "make it most difficult for him" at the place he prefers to attack, says Longman.
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 Lawrence Livermore National Laboratory, a Department of Energy agency in Livermore, California, is working on a device, called RadNet, which he thinks will be ready to test in a few hundred cell phones in 18 months.
Funding at U.S. government labs and agencies has slowed, however, perhaps due to uncertainty over the budget priorities of the next administration. Even so, the U.S. Department of Homeland Security has said it will financially 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 unexpected role in protecting national security.
