Scientists Probe North Korea Nuke Test

[align=left]Scientists Probe North Korea Nuke Test
AP | October 9 2006
North Korea sets off an earthshaking explosion _ and claims it was nuclear. Was it? For scientists, that was not a quick and easy question to answer. [/align]
Like earthquakes, large explosions send out shockwaves that can be detected on seismographs. Big nuclear bombs make big waves, with clear signatures that make them fairly easy to detect, analyze and confirm that they were caused by splitting atoms. But smaller blasts _ as North Korea's appears to have been _ are trickier to break down.
The natural sound of the Earth, with its constant seismic activity of tectonic plates grinding together, complicates the task of trying to determine whether a smaller blast was caused by conventional explosives or a nuclear device, said Xavier Clement of France's Atomic Energy Commission.
He likened the problem to trying to "detect the violins or a flute in a symphony orchestra when you are playing the cymbals."
His agency estimated the North Korean blast at around 1 kiloton or less _ equivalent to the explosive force of 1,000 tons of TNT. For a nuclear device, that would be so weak that the French defense minister suggested that "there could have been a failure" with the North Korean reported test.
Clement said it could take days before scientists can declare with certainty whether the explosion was nuclear. And when blasts are very weak, "we could be in a situation where we cannot tell the difference between the two," he said.
The United States, Russia, China, Japan and South Korea are among the countries with equipment strong enough and close enough to monitor a North Korean test, said Russian nuclear physicist Vladimir Orlov of the Moscow-based PIR Center, a nonproliferation think-tank.
"It takes days, dozens of lab hours, to evaluate results. Now we can have only a rough estimate," he said.
The Comprehensive Nuclear Test Ban Treaty Organization, or CTBTO, has about 200 stations worldwide designed for monitoring nuclear tests as part of what it hopes will become the world's most reliable source for such tests. But until the treaty comes into force, the data are not made public, only released to governments and vetted partners.
Seismic data comes in almost immediately, and is usually passed to governments within an hour or so. Their scientists must decide what the numbers and graphs mean.
With the North Korean blast, there were wide variations. While the French atomic agency estimated around 1 kiloton and South Korea's geological institute half of that, Russia's defense minister expressed "no doubt" that North Korea detonated a nuclear test and said the force of the underground blast was equivalent to 5,000 to 15,000 tons of TNT.
"People have different way of cross cutting the data and interpreting them," said Lassina Zerbo, director of the International Data Center at the CTBTO, which is based in Vienna, Austria.
The test ban treaty, which bans all nuclear explosions, will not enter into force until it has been ratified by 44 states who possess either nuclear power or research reactors. So far 34 have ratified it. Holdouts include the United States, China, India, Pakistan, Israel and North Korea.
The CTBTO's stations are more extensive than those used by most countries. They monitor seismic events but also underwater data, radioactive particles in the air and radiowaves.
"Within 72 hours we will have full data. Then all this will be available to member states," said Zerbo.
While the North Korean explosion was small, potentially complicating monitoring efforts, sensors in South Korea were likely close enough to categorize it as nuclear, if that is what is was, said Friedrich Steinhaeusler, professor of physics at Salzburg University.
A nuclear blast also gives off a clear signature _ a clear graph of peaks and curves _ that differentiates it from other kinds of shocks, he added.
"We'll have the confirmation soon," he said.

[align=left]N.Korea nuke test relatively small: scientists
Reuters / Michael Perry | October 9 2006
North Korea's nuclear test on Monday might have been a "mini-nuke" explosion possibly as low as one kiloton, comparable to some small tests by India and Pakistan in 1998, scientists said on Monday.[/align]
The U.S. Geological Survey said it had detected a 4.2 magnitude quake in North Korea at 10:35 local time (0135 GMT) on Monday, confirming a similar report from South Korea.
Gary Gibson, senior seismologist at Australia's Seismology Research Center, said a 4.2 magnitude quake would be the result of a one kiloton explosion.
"It depends on how the thing is set off. There is not a perfect correlation between magnitude and the yield and depends to some extent on the rock type they set it off in," he said.
"It is a relatively small nuclear test."
A U.S. intelligence source agreed that a preliminary examination of the data did not indicate a large blast or a series of explosions. But the source stressed that analysts were still working toward a definitive evaluation.
"It's premature because they're still evaluating the data," the source said.
The RIA news agency quoted on Monday Russian Defense Minister Sergei Ivanov as saying that the nuclear device tested by North Korea ranged between five and 15 kilotons.
The nuclear weapon the United States exploded over Hiroshima in 1945 produced a 12.5-kiloton yield.
In 1998, India carried out five underground nuclear tests at Pokharan in the western desert state of Rajasthan and declared itself a nuclear weapons state.
The total yield of the first round of blasts measured near 60 kilotons. Two days later, it exploded sub-kiloton devices that scientists said made it capable of conducting computer tests not covered by the Comprehensive Test Ban Treaty.
"Our biggest one was in the vicinity of 45 kilotons. That was thermo-nuclear," said S.K. Malhotra, head of the public awareness division of the Department of Atomic Energy.
Nuclear analyst Andrew Davies, from the Australian Strategic Policy Institute, said if the North Korean test yield was only a kiloton, Pyongyang may be disappointed.
"A kiloton is a very low yield and would tend to suggest, I would have thought, that the device was not all they hoped it would be," Davies told Reuters.
"If a nuclear, plutonium bomb fizzles, you can still get one or two kilotons quite easily. You still get a significant energy release. But an efficient device will give you more like 20 (kilotons)."
MINI NUKES
The United States has said it is interested in developing so-called "mini nukes" -- nuclear weapons with a yield of less of than five kilotons.
Indian nuclear scientists said they thought the North Korean test was an indication that the country was going for smaller devices to ensure effective delivery.
"They are concentrating more on the small devices because of reliability of launching and effectiveness," said A.N. Prasad, former chief of the Bhabha Atomic Research Center, India's top nuclear research facility.
"If the situation demands, they can scale it up, which is not difficult. This is the best approach now."
After India exploded its devices, arch foe and neighbor Pakistan rushed to conduct its own tests.
Within days it had conducted six tests, although claims related to the number, strength and yield of the tests were doubted by scientists in India and the United States.
Pakistan said two nuclear tests had a total yield of between 34-48 kilotons, while three others were sub-kiloton. It said a sixth test yielded 10-15 kilotons.
The Southern Arizona Seismic Observatory said the two major tests yielded 9-12 kilotons, while the sixth yielded only 4-6 kilotons.
A source in Beijing who is close to the North Korean regime said Pyongyang had detonated a neutron bomb, designed to release larger amounts of deadly radiation than other nuclear weapons. There was no immediate confirmation of the claim.
(Additional reporting by Krittivas Mukherjee in MUMBAI, Simon Cameron-Moore in ISLAMABAD, James Grubel in CANBERRA and David Morgan in WASHINGTON)