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sweet stuff i see that and raise you thisFINDING HIDDEN NUKES
BY JIM WILSON
Published on: May 1, 1997
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Gerhardt's claim jibed with an earlier news story. In March 1993, South Africa President F.W. de Klerk had admitted that his country had at one time possessed a secretly developed, small nuclear arsenal, but that it had junked it in 1989 in order to sign the Nuclear Non-Proliferation Treaty. Had Gerhardt been a more credible source, the mystery might have been solved. The problem was that Gerhardt had been convicted of spying for the Soviet Union. And so to this day, the incident lacks a verifiable explanation.

The convoluted story, which is not widely known outside the intelligence community, underscores what is perhaps the greatest challenge facing scientists as the world's major powers begin to dismantle their nuclear arsenals. If an aboveground nuclear explosion like the one that is presumed responsible for the Vela Flash is difficult to prove, imagine the difficulty in ferreting out evidence of a blast that was intentionally hidden.

"If a country wants to evade detection, you can think of a variety of subterfuges," Charles Carrigan, a geophysicist and an expert on the Comprehensive Test Ban Treaty (CTBT), told Popular Mechanics during our recent visit to Lawrence Livermore National Laboratory (LLNL), in Livermore, California.

Currently, one of the best hiding places for a nuclear test is in a mine shaft, says Carrigan. But after the treaty goes into effect, in about two years, even the deepest hole will be a less secure hiding place. "A 1-kiloton explosion can look like a magnitude 4 earthquake," Carrigan explains. And so within minutes of a nuclear detonation, the CTBT technicians that monitor the seismic activity, atmospheric sound waves, underwater sound waves, and radioactive particle and gas detection data streaming into the International Data Center in Vienna, Austria, will have their first signal that something is amiss.

Then the hard work begins. The data from the sensor network will identify the approximate site of the explosion within about 400 sq. miles. Then someone would have to inspect the suspect terrain, most likely a mining region, and bring back legally acceptable proof that a nuclear detonation–rather than an earthquake or mining explosion or accident–occurred.

The key to making this happen, says Carrigan, is the ability to detect small amounts of two exotic gases–xenon-133 and argon-37–produced in nuclear explosions as they rise to the surface along natural faults and cracks. "If you detect them coming up fissures or faults, that means something happened very recently," Carrigan says. By "small" he means really, really small. Finding evidence of hidden nukes by detecting these gases at ultralow levels is the equivalent of finding a ping-pong ball filled with chemicals in Lake Michigan.

To do this, Carrigan and colleagues Jay Zucca–a fellow geophysicist–Ray Heinle, Bryant Hudson and John Nitao (all physicists) performed an ingenious experiment. In 1993, they simulated a deeply buried underground nuclear explosion by mixing small amounts of two non-radioactive gases–helium-3 and sulfur hexafluoride–inside an underground chemical explosion at the Department of Energy's Nevada Test Site.

Dubbed the nonproliferation experiment, the chemical explosion did not produce any new cracks in the ground, but still, over time, the two gases showed up in metal air-sampling tubes pushed between 3 and 15 ft. into the ground in existing fissures.

The gases appeared during periods of low atmospheric pressure, such as just before or during storms, often snowstorms, when the pressure allowed the gases to rise to the surface along the faults. Nearly 200 gas samples were taken over about one and a half years. The heavy sulfur hexafluoride appeared first, 50 days after the detonation, with the lighter helium showing up more than a year afterward, at 375 days.

This surprising result occurred–just as computer models predicted–because the heavier sulfur hexafluoride gas spread out less and moved directly up the fractures, Carrigan says. Meanwhile, the helium diffused sideways into the porous structure of the rocks and therefore took longer to rise. (See illustration above.)

The researchers predict that if a 1000-ton nuclear test were staged under atmospheric conditions similar to the 1993 experiment, xenon-133 and argon-37 produced by the nuclear explosions would be detectable at 50 and 80 days after the detonation, respectively. If low-pressure systems roll in, they would turn up even sooner. Precise timing is important, because xenon's half-life is 5.3 days and argon's is 34.8 days. A gas has reached its half-life when there is half as much of it as the initial amount.

For this reason, the LLNL team believes on-site inspections for nuclear tests should be timed with the arrival of the low-pressure systems that cause storms. They also suggest that air sampling stations be placed in existing cracks and fissures, even hundreds of yards from a test's estimated ground zero, rather than having placement based solely on proximity to the estimated ground zero. "We can't absolutely guarantee there won't be cheating," says Carrigan. "But we've made it much more difficult."

http://www.popularmechanics.com/science/law_enforcement/1280891.html?page=2&c=y