Stopping porta-nukes
Christopher Helman, Forbes Global, 12.24.01

A terrorist sidles into a crowded train station with a radioactive bomb tucked into his suitcase. Do we have the technology to spot it?

Dirty nukes--suitcase-size bombs made of explosives studded with scavenged chunks of radioactive material--could become the next tool of terrorism, far more devastating than hijackings and anthrax. Can they be stopped?

"If a nuclear attack comes, it won't be from an ICBM but more likely in the hold of a container ship," says Paul Leventhal, president of the Nuclear Control Institute in Washington, D.C. "The threat is very real. It's hard to grasp because it's so unthinkable. Denial is a key factor in our weak state of security."

New technology is the key to strengthening security. Until recently the only equipment for spotting a suitcase bomb was an unwieldy machine the size of a refrigerator that used liquid nitrogen to cool crystal detectors down to 184 degrees Celsius below zero and took hours to produce a reading. U.S. federal agencies are deploying new detectors that put the Geiger counter's 90-year-old technology to shame. They are fast enough to scan trucks and cars as they pass through toll booths, portable enough to be used almost anywhere and sensitive enough to distinguish between a weapons-grade isotope and the less dangerous form in an X-ray machine.

Berkeley Nucleonics, a privately held company in San Rafael, California, sells an $8,000 handheld detector, called SAM 935, that uses sodium iodide crystals and powerful software that can identify 90 isotopes in one second. Berkeley's chief rival, SAIC in San Diego, has sold hundreds of its cesium iodide handheld screeners to the FBI and other agencies.

SAIC also makes larger "portal" detectors that look like the metal detectors at airports. Packed into two suitcases, these $10,000 snoopers also use sodium iodide crystals to spot radiation on people, but they can't distinguish between isotopes. That requires a scan with a more precise handheld device. "This time next year there will be hundreds of these used at critical points across the U.S.," says James Winso, a director of SAIC.

Signs of the growing risk occurred long before Sept. 11. Since 1993 nearly 400 cases of illegal trafficking in nuclear and radioactive materials have been tracked by the International Atomic Energy Agency in Vienna. In 18 instances small amounts of bomb-grade uranium or plutonium were involved. In July four men were arrested in Georgia, the former Soviet republic, on a charge of plotting to sell 2 kilograms of enriched uranium 235; it takes 25 kilos of it to build a bomb.

Customs agents carry devices like basic Geiger counters in their shirt pockets to measure radiation exposure. But though the Geiger counter spots radiation easily, it can't determine which isotope is present and therefore is unable to tell whether danger is at hand. Geiger counters use an electrically charged wire inside a metal tube filled with methane and argon gas. A window at one end lets in ionizing radiation from a decaying isotope. The radiation ionizes an atom in the gas mixture, setting off a cascade of electrons that hit the wire and register as an electric pulse counted by a meter or amplified into the familiar "click-click."

The newer detectors forgo wires and gas in favor of highly engineered crystals made from sodium iodide or cesium iodide. These crystals, the size of ice cubes, are grown slowly in ovens heated as high as 980 degrees Celsius, increasing by just one centimeter a day. They are so dense that they can absorb radiation entirely. When exposed to an isotope, the crystals flash for 50 billionths of a second. Since every isotope that spews gamma or X rays or charged particles does so in a unique way--an atomic fingerprint, of sorts--the color and intensity of the flash tells the detector which isotope is present and in what quantity.

SAM 935, introduced in 1995 and upgraded annually, looks like a big can of shaving cream and has a crystal positioned inside the opening at one end. Once an isotope causes the crystal to flash, a photosensitive cathode releases electrons into a vacuum tube where a chain reaction produces a cascade, as in the Geiger counter. Resulting electrical pulses are analyzed by software that can determine which isotopes are present.

Founded in 1960, Berkeley Nucleonics, which peddles measurement devices to the nuclear and chemical industries, has annual sales of less than $50 million. It has sold hundreds of the new detector units to the military, the Environmental Protection Agency, the Department of Energy and emergency response teams.

Terrorists could find a way around some of these scanners--for example, by lining a suitcase with lead. SAIC and Berkeley Nucleonics can respond with additional detectors that pick up neutrons. In the end nuclear security comes down to a battle of brainpower.

As Winso says, "A lot of these terrorists have fine German or American engineering educations. They're smart."

Let us hope our guys are smarter.