Officials to analyze air particles to verify blast

The South Korean government is launching a detailed analysis of North Korea’s fourth nuclear test on Wednesday that includes a review of image data to check the activity that took place around the nuclear testing site.

Domestic and international experts are also tracking down possible airborne radioactive particles released by the test to confirm whether North Korea did detonate a hydrogen bomb as it asserted.

The Korea Institute of Nuclear Safety, the Korea Atomic Energy Research Institute and other relevant agencies plan to mobilize all their efforts to collect air samples, as Korea has been equipped to do so since North Korea’s first nuclear test in 2006.

Detection of radioactive particles, or radionuclides, will be especially helpful in determining what kind of a test was conducted and if it was with a hydrogen bomb as claimed.

North Korea on state television announced that it had successfully tested its first hydrogen bomb some two hours after a seismic event was detected by meteorological agencies around the world on Wednesday morning.

However, experts have been skeptical over whether a hydrogen bomb was really what was detonated based on the seismic activity, which did not exceed a magnitude of 5.1-earthquake on the Richter scale.

This was interpreted by some analysts to be too weak for a hydrogen bomb.

The seismic readings are in line with North Korea’s previous underground nuclear tests in 2006, 2009 and 2013 that took place at the Punggye-ri site in Kilju County, North Hamgyong Province.

“Following a nuclear test, a large amount of gas is released,” a South Korean intelligence source said. “In the case that xenon or krypton is collected, it can be determined whether it was a plutonium or uranium explosion.”

Radioactive chemicals such as xenon or krypton, so-called smoking guns, can help demonstrate whether the North tested a plutonium- or uranium-fueled device.

Xenon isotypes, a radioactive material, would indicate that the North tested a plutonium-fueled device. Krypton would indicate a uranium-fueled device.

Pyongyang’s first two tests were uranium-fueled; however, the analyses to determine whether North Korea used an enriched-uranium device for its third nuclear test in February 2013 have proven inconclusive.

In the case that it was, in fact, a hydrogen bomb, as Pyongyang claims it was, helium or lithium should be detected.

The U.S. Air Force has deployed its WC-135 Constant Phoenix, which has air-sampling equipment, to collect and analyze gas and debris in the atmosphere.

Japanese Chief Cabinet Secretary Yoshihide Suga said that its Air Force has also deployed planes to collect air samples to test possible radioactive materials at its Japan Chemical Analysis Center. Russia and China are monitoring radiation levels, too.

“When gas is leaked after a nuclear test, there is a two to four-week time frame to detect it,” a South Korean government official said.

After Pyongyang’s first nuclear test, a station in northern Canada detected traces of xenon in the air. However, it was difficult to collect samples from the second test onward.

BY JEONG YONG-SOO, SARAH KIM [kim.sarah@joongang.co.kr]