Tuesday, October 10, 2006 - Page updated at 12:00 AM

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PARIS – Was North Korea's nuclear device a dud, as some Western experts suspect?

The apparent low yield of the North's test could signal that its scientists, working largely in isolation, haven't quite perfected the deadly art of efficiently splitting atoms.

More than 60 years after the United States first tested a plutonium weapon — partly because scientists weren't sure that it would work — the technology is still tricky for novices to master.

"The devil is in the details," French nuclear proliferation expert Bruno Tertrais said. "It's like cooking. The fact that you have the recipe does not make you a chef."

North Korea is widely thought to have been seeking to make bombs from plutonium, the same material used in the device that the U.S. first tested on July 16, 1945, ushering in the atomic age. Robert Oppenheimer, who oversaw the U.S. weapons program, on that historic day lost his $10 bet that the bomb — nicknamed "the Gadget" — would not detonate.

Only the North Koreans likely know what sort of explosion they were hoping for and whether the test was a success, as they claimed.

But there's also a possibility that the device — if it was indeed nuclear — suffered what experts call "a fizzle," when the fissile material that provides the bang, likely plutonium in North Korea's case, detonates only partly.

"The working assumption is that more likely than not it was a nuclear bomb, although not a successful one," said one U.S. official, who requested anonymity because the matter is highly classified. It will take time and more information for analysts to reach a conclusion, he said.

The blast, which reportedly occurred in an underground shaft not far from North Korea's northeastern border with China, created a tremor that registered 4.2 on the Richter scale, according to the U.S. Geological Survey.

Experts said the magnitude was fairly small for a nuclear test, equating to 300 tons to 800 tons of TNT. By comparison, the nuclear bomb that fell on Nagasaki, Japan, in August 1945 was the equivalent of 20,000 tons of TNT.

The surest way to determine whether there was a nuclear explosion would be to collect air samples downwind of the blast site and test them for radioactive fallout. The United States operates aircraft capable of collecting such samples, but experts said it could take time for radioactive gases to escape from underground.

"It will take some time to sort out what this was and what this wasn't. People should be cautious about jumping to early conclusions," said Daryl Kimball, the executive director of the Arms Control Association, an advocacy group.

The apparent low intensity of the explosion was a key reason for suspicions that it was a dud or, at best, only partially successful.

Only Russia estimated that it was a relatively large explosion — equivalent to the force that would be unleashed by 5,000-15,000 tons of the conventional high-explosive TNT.

France and other nations had far lower estimates, ranging from 500-1,000 tons of TNT, prompting the French defense minister to comment "that there could have been a failure."

South Korea also said that it wasn't certain that the North's test was a success and that resolving that doubt would take about two weeks.

France's atomic energy agency did not want to comment further today — partly, a spokeswoman said, because it was concerned that discussing where North Korea might have gone wrong could help it fix any problems for next time.

While there is evidence that North Korea got Pakistani help with its nuclear program, the isolated, communist country also has had to figure out a lot of technical bomb-making details itself — another likely factor in a possible failed test, said Vladimir Orlov of the PIR Center, a nonproliferation think-tank.

"Both intellectually, technologically and financially, they are really in practical isolation, which is relatively good news," said Orlov.

The apparent low yield, he added, "indicates that the North Koreans really have trouble making what ordinary people would call a nuclear bomb, they really have a primitive nuclear device."

World leaders didn't wait for the details to denounce North Korea's claims.

"Such a claim itself constitutes a threat to international peace and security," President Bush said. "Once again, North Korea has defied the will of the international community, and the international community will respond."

South Korea called the test an "intolerable provocative act" and put its military on heightened alert.

China, Russia, Japan, France and the European Union joined the chorus of condemnation.

China appeared stunned, describing the test as "brazen," and said, "The Chinese government is firmly opposed to this."

Copyright © 2006 The Seattle Times Company


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