TBILISI (Georgia): In the 1970s, scientists in the former Soviet Union developed scores of powerful radioactive devices and dispatched them to the countryside for a project known cryptically as Gamma Kolos, or “Gamma Ears.” Its purpose: to deliberately expose plants to radiation and measure the effects.

Some of the tests were aimed at simulating farming conditions after a nuclear war. In rugged eastern Georgia, researchers bombarded wheat seed with radiation to see if the plants would grow better. All the experiments used a common source of radiation, a lead-shielded canister containing enough radioactive cesium 137, US officials now say, to contaminate a small city.

The experiments stopped long ago, but last year’s terrorist attacks on New York and the Pentagon have kindled an intense interest in Gamma Kolos that revolves around a single question:

Where is the cesium now?

Spurred by fears of a “dirty bomb” attack that could spread radioactive poisons across major cities, US and international nuclear experts have begun searching former Soviet republics to recover the remains of the Gamma Kolos project before someone else does.

Unknown in the West until recently, the Soviet project is viewed as especially dangerous because its cesium devices could be easily exploited for terrorism: small, portable and possessing a potent core of cesium chloride in the form of pellets or, more frequently, a fine powder. Cesium 137, a silvery metal isotope used commonly in medical radiotherapy, emits powerful gamma radiation and has a half-life of three decades.

“It’s like talc — extremely dispersible,” said Abel Gonzales, director of radiation and waste safety for the International Atomic Energy Agency, the United Nations-chartered nuclear watchdog. “You don’t even need a bomb. Just open a can and people will die.”

With heightened urgency and new backing from the US Energy Department, the IAEA led a 10-month sweep of the former Soviet republic of Georgia, now a troubled but independent state. The search turned up five of the Gamma Kolos devices, all of which are now in safe storage. Four more devices have been found in Moldova, while in Russia US officials are helping to construct security systems for agricultural research centres where large quantities of powdered cesium are stored.

But elsewhere across the old Soviet empire, the search is hampered by a lack of funding and a dearth of information. None of the cesium devices is known to have been stolen, but in some Central Asian states there are no records showing how many of the devices exist or what has happened to them. Estimates of the total number of devices are vague — “anywhere from 100 to 1,000,” not counting stocks of cesium in loose storage in Russia, a senior IAEA official said.

Russia is beginning to cooperate in the search, although it cannot yet account for all the cesium, Bush administration officials said.

“I can tell you the Russians themselves are very worried about the cesium that’s still out there in some of the (former Soviet) republics,” a top official of the US Nuclear Security Administration said, speaking on the condition of anonymity.

At least some of the republics share that concern. In Georgia, officials are combing the countryside with radiation detectors following a string of accidents in which civilians stumbled upon abandoned radioactive devices and suffered severe radiation burns. In at least one instance, the radioactive device had drawn the interest of local businessmen who were hoping to sell it on the black market, according to US and Georgian government officials.

“We’re not a nuclear country, yet we have these problems with nuclear material,” said Zurab Tavartkiladze, Georgia’s deputy environmental minister. “How many more are out there? We don’t know, because we don’t know how many existed to start with.”

While the United States has spent billions of dollars in the past decade helping secure or destroy Soviet-era nuclear and chemical weapons, only since September 2001 has the US effort expanded to include nonfissile radioactive material such as cesium 137. The interest first arose from intelligence reports last fall that Al Qaeda terrorists were exploring the use of radiological weapons known as dirty bombs. It grew with the discovery by US troops of detailed bomb-building instructions in Afghan caves used by Al Qaeda forces. In June, the Justice Department announced it had foiled an alleged Al Qaeda plot to explode such a device in a US city, possibly the capital.

The concerns prompted Energy Secretary Spencer Abraham in September to call for a global housecleaning to find and secure material that could be used in dirty bombs — a threat that was made “horrifyingly clear” by the events of the previous 12 months, he said.

“After September 11 (2001), there could be no doubt, if there ever was one, that terrorists would use nuclear materials to harm innocent citizens of the civilized nations of the world — if they could acquire them,” Abraham said.

Although far less lethal than traditional nuclear weapons, dirty bombs could be attractive to terrorists because they can inflict widespread disruption for relatively little cost. With conventional explosives and a few ounces of cesium 137 or strontium 90, a dirty bomb could contaminate large swaths of real estate with dangerous radiation, unleashing panic and rendering some areas uninhabitable for decades.

In a computer simulation of a dirty bomb attack on New York, the detonation of 3,500 curies of cesium chloride in Lower Manhattan — about 50 grams or 1.75 ounces — would spread radioactive fallout over 60 city blocks. Immediate casualties would be limited to victims of the immediate blast, but the aftereffects, including relocation and cleanup, would cost tens of billions of dollars, said Michael A. Levi, a physicist and director of the Federation of American Scientists’ Strategic Security Project, which conducted the study.

“The financial costs, from the loss of property to business losses, could be huge,” Levi said. “People may refuse to return, and others may be unwilling to travel to the area. The threshold for scaring people away from some activities is very low.” —Dawn/LAT-WP News Service (c) The Washington Post