Authorities in the Central Asian Republic of Kyrgyzstan are investigating why a train traveling from Kyrgyzstan to Iran was carrying radioactive cargo.
The amount of radioactive material was not enough to make a weapon.
But the Kyrgyz government says it still doesn't know how or when the material was placed on board the train.
On Dec. 31, 2007, emergency workers gathered at Belovodskaya station in Bishkek, the capital of Kyrgyzstan, to greet a train that was turned back after it set off radiation detectors in Uzbekistan en route to Iran.
Specialists pinpointed one car, which was emitting radiation at levels 1,000 times higher than normal.
Emergency workers say the source lay in a pile of dirt and garbage beneath 50 tons of scrap metal.
Kyrgyz newspapers report that this is the third time in three years authorities have intercepted trains leaving Kyrgyzstan with radioactive cargo.
In this case, Kyrgyz officials say the radioactive substance consisted of several grams of cesium-137, which is often used in medical and industrial instruments.
Alexander Melikishvili, of the James Martin Center for Nonproliferation Studies, says that in powder form, cesium-137 could also be used to make a dirty bomb.
"From the perspective of a terrorist, the ideal device would entail cesium-137, with some sort of conventional explosive," he says.
There wasn't enough cesium-137 aboard this train for a weapon, prompting some to conclude it accidentally got mixed in with the scrap metal.
The Central Asian republics are littered with former Soviet nuclear test sites, uranium-processing plants and radioactive waste dumps.
Roger Kangas of the National Defense University in Washington, D.C., says cash-strapped governments like Kyrgyzstan's have a hard time securing this radioactive legacy of the Soviet Union.
"When you come up against porous borders, problems of corruption, the profitability of perhaps shipping some of this material out, you can see they're really up against a tall challenge here," he says.
Last spring, two former government officials stood trial in neighboring Tajikistan for allegedly trying to sell canisters of plutonium and cesium-137 on the black market.
Watchdog organizations say nuclear smugglers are arrested in this region every year.
To combat the trade in radioactive goods, the United States and Russia have distributed radiation-detection equipment at Central Asian border checkpoints.
But before it was stopped last month, Kyrgyzstan's radioactive cargo train apparently passed through at least two of these borders undetected.
"The radiation control at the borders is the line of defense that … if it's properly carried out, stops the illicit trafficking," says Melikishvili, the nonproliferation expert.
The Kyrgyz government announced Thursday that it would request help from the International Atomic Energy Agency to install more radiation detectors on its borders.