September 07, 2017 12:25
The Nuclear Safety and Security Commission on Wednesday admitted it has failed to detect any radiation from North Korea's latest nuclear test.
The NSSC and the Korea Institute of Nuclear Safety said air-sampling equipment on planes and ships and land radiation detection stations collected samples to find traces of radioactive xenon on Monday, a day after the North's latest nuclear test.
Radioactive xenon rarely exists in natural environments and is usually created by nuclear explosions and therefore considered the "smoking gun" in detecting such tests. But none has been found.
Two types of radioactive xenon exist -- Xe133 and Xe135. They can be used to determine whether uranium or plutonium were used depending on their ratios. But the agencies have had little success in collecting it to find clues after any North Korean nuclear tests.
A small amount of radioactive xenon was collected in January last year, when North Korea conducted its fourth nuclear test, claiming it was a hydrogen bomb, but the amount was too small for proper analysis.
Experts say the half-life of xenon is too short, and its tendency to dissipate in the atmosphere makes it difficult to detect. Nuclear experts said the ideal time window is five to 10 days.
"There were strong southeasterly winds around Punggye-ri at the time of the latest North Korean nuclear test, causing most of the radioactive substances to be blown into Russia." Yim Man-sung at the Korea Advanced Institute of Science and Technology said. "The winds later shifted direction southward, but it looks like most of the xenon had dissipated."
Search areas and radiation density also play a role in the success or failure of detecting radioactive xenon. Amid reports that a tunnel at the Punggye-ri test site is at the risk of collapsing, there are growing fears of a possible heavy leak of radiation. The test site sits under a very thick layer of granite, which contained radiation leakage until now.
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