Smart Detectors Against Dirty Nukes

March 12 -- It's a nightmare scenario that could take place in the not-too-distant future, say some experts. Terrorists craft and explode a "dirty bomb" — an explosive weapon laced with nuclear or radioactive material such as cesium or cobalt.

Security experts recently testified before Congress that such bombs won't kill as many people as an outright explosion from a true nuclear weapon. But they said a dirty bomb could spread invisible and deadly radiation for miles and contaminate areas for years — making such devices an ideal weapon of terror.

In order to ward off such potential disasters, the U.S. government is taking several steps, including the use of new, "smart" radiation detectors.

According to experts, traditional radiation detectors — Geiger counters — don't tell users enough about material that's giving off waves of radiation.

"As you get closer, the Geiger counter clicks faster," says Ralph James, associate lab director for the Energy, Environment and National Security Group at Brookhaven National Labs in Upton, N.Y.

But that happens if the material is plutonium 239 — a material in nuclear weapons — or americium 241 — a material used in smoke detectors in every house. "That [clicking] is simply not enough information when detecting a radiological weapon," says James.

Seeking Radioactive Signatures

The new sensors, called gamma ray detectors, use exotic chemicals such as germanium and cadmium zinc telluride. More sensitive to certain types of radiation, these chemical sensors help give searchers a more accurate idea of the kind of nuclear threat they are facing.

Every radioactive element gives off a certain unique pattern or "signature" of energy, says James.

"They're just like different frequencies on a radio dial," he says. "In smart detectors, we have the ability to discern isotopes in weapons — like uranium or plutonium — from a wide range of naturally occurring isotopes."

In other words, the smart detectors will give security and law enforcement personnel a better way to screen out potentially false alarms — such as a shipping container that really contains only minute amounts of cesium for medical experiments.