RADIOACTIVE gases that could have come from North Korea’s nuclear test in February have unexpectedly been detected, possibly providing the first “smoking gun” evidence of the explosion.
However, the 9 April measurement by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) – almost two months after Pyongyang said it had carried out the underground detonation – has given no indication of whether plutonium or highly-enriched uranium was used.
The time that had passed before the so-called Noble gases were picked up made it “very difficult” to distinguish between the two fissile materials, said CTBTO spokeswoman Annika Thunborg.
The isolated east Asian state is believed to have tested plutonium bombs in 2006 and 2009. Any switch to uranium would increase international alarm as it could enable Pyongyang to greatly expand its arsenal.
Pyongyang’s third nuclear test was registered virtually instantaneously via seismic signals around the world, but no radioactive traces that would have constituted conclusive proof were found in the weeks afterwards.
The Vienna-based CTBTO, which has a worldwide network of monitoring stations, said in mid-March that it was highly unlikely any such radioactivity would be detected.
However, yesterday’s statement said it made a significant detection of radioactive Noble gases two weeks ago in Takasaki, Japan, about 620 miles from the test site. Lower levels were picked up at another station, in Ussuriysk, Russia.
“Detection of radioactive noble gas more than seven weeks after an event is indeed unusual. We did not expect this and it did not happen in 2009,” the CTBTO said, referring to the reclusive country’s previous nuclear test.
Large amounts of xenon gases are produced in fission, a nuclear reaction occurring both in nuclear arms and reactors.
“We are confident that the (North Korean) test site is among the possible source regions,” the CTBTO said. But it could still not “exclude completely” that the radioactive traces came from somewhere else.
North Korea abandoned plutonium production six years ago in response to international pressure, but later acknowledged that it had built facilities to produce enriched uranium, which can also be used in bombs if refined to a high degree.
Experts say plutonium, a byproduct of nuclear reactors, can be difficult to use as bomb material because specifications have to be precise. It could be easy for North Korea to make large quantities of highly enriched uranium.