Now this is pretty damn interesting:

Researchers were scratching their heads earlier today at a meeting convened by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) over puzzling results from last month’s nuclear test by North Korea. While the test produced a clearly recognizable seismic signal that was picked up by CTBTO’s worldwide network of sensors, the organization’s atmospheric detectors failed to pick up a whiff of the expected radionuclides in air. Even a deep underground test is usually expected to leak radionuclides, so their absence in this case caused quite a stir. Anders Ringbom of the Swedish Defense Research Agency in Stockholm says CTBTO’s detectors for radioactive noble gases—a telltale signature of a nuclear test—can pick up a couple of hundred atoms from a cubic meter of air. On the lack of a signal, he said: “I was a little surprised, yes.”

Some 400 scientists gathered here, CTBTO’s home base, this week to discuss the results of a series of studies carried out by external researchers over the past year to test the capabilities of the system for detecting clandestine tests and to consider other scientific uses for the wealth of data collected. The system comprises 337 sensors across the globe looking for seismic signals, radionuclides, hydroacoustic signals in the oceans, and very low frequency infrasound in the air. Seismologists at the meeting say that the 25 May Korean test was an unmistakably man-made event and showed characteristics that make it almost certainly a nuclear rather than a chemical explosion. But the presence of radioactive xenon is considered the smoking gun for the nuclear nature of an explosion—and it wasn’t detected.

Here’s the problem: if the scientific community does not find evidence of xenon, then this raises questions about our ability to effectively monitor and enforce compliance with the Comprehensive Test Ban Treaty (CTBT), which the United States has failed to ratify. Susan Watts of the BBC writes:

But there was one thing everybody in the room wanted to know. Had the network of sensors picked up radionuclides from the North Korean explosion two weeks ago? Seismologists here today say they are comfortable that explosion was a nuclear test, but detecting radionuclide evidence in the form of radioactive gas is the “smoking gun”. And the big news here is that they have not found that signal.

What’s more, scientists don’t really seem to know why. One delegate, an expert on radionuclide detection from Sweden, told the conference how well the network performed after North Korea’s nuclear test in 2006. Twelve days after that event the network picked up just a few hundreds of atoms of the noble gas Xenon 133 in Canada. He confessed to being “surprised” that this time round, so far, there has been nothing. He said he is sure the sensors are working properly. So why might there be no signal, and does it matter?

The eminent seismologist Professor Paul Richards from Columbia University implied it didn’t matter so much. The network includes a range of technologies – using seismic, infrasound, hydroacoustic and radionuclide technologies precisely to give the world what he described as a “a quiver of arrows”. Thus if one arrow doesn’t hit the target, then others will; if one detection set-up sees no nuclear signature, others will. And his personal view is that this was most likely a nuclear test.

So was there a deliberate attempt by the North Koreans to contain the explosion? Or was the explosion contained by accident? Some larger yield nuclear explosions can apparently “melt” the rock around them, so less noble gas seeps out. Attempts to explain the lack of a noble gas signal remain educated guesses at the moment. The official line here is that all this highlights the need for more countries to ratify the Treaty, so that it can come into force, thus allowing on-site inspection teams to move in to check out such tests.

In the meantime, scientists here might be keeping their fingers crossed that something shows up soon, but they seem already to be resigned to the possibility that it may not.

Still, some news sources are raising the possibility that the North Koreans faked an explosion:

eports indicate that a global network of sensors designed to verify nuclear testing has failed to pick up radioactive gases from North Korea’s nuclear blast, which indicates that the country might have used conventional explosives to mimic a nuclear test.

North Korea conducted what it claims was its second nuclear test on May 25 this year. Within seconds, a global network of seismographs had detected the shock wave from the blast.

The seismographs are operated by the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), a Vienna-based body that would enforce a global ban on nuclear testing if enough nations were to sign up to the treaty.

The CTBTO seismographs showed that the tremors caused by the explosion were of magnitude 4.5, far larger than the nation’s first nuclear test in October 2006.

According to a report in Nature News, the seismic signature of the test strongly suggested that the blast was man made, but the CTBTO hoped to use a follow-up set of measurements to verify its nuclear nature. […]

Zerbo points out that the CTBTO network is far more complete in 2009 than it was in 2006 and that all stations were operational at the time of the test.

“If we didn’t measure it, it’s unlikely that anyone outside of North Korea’s borders did,” he said.

The lack of isotopes has become an interesting puzzle for proliferation researchers. It could mean that the North Koreans used conventional explosives to mimic a nuclear test.

Such a mock test would be unusual, although not unprecedented.

In the 1980s, the United States government set off several multi-kilotonne chemical explosions to test how various weapons and communication systems would respond to a nuclear blast. (ANI)

Given that the last test struck many as a likely fizzle, I suppose this isn’t outside the realm of possibility.