Officials said if plutonium were used, it could be remnants of a dismantled nuclear reactor and the amount would be limited, but if uranium were used in the threatened detonation, it could indicate North Korea was moving to expand its nuclear arsenal through uranium enrichment, The New York Times reported Tuesday.
Since North Korea announced in January that it would conduct a third nuclear test, officials and analysts said they suspect the reclusive country might detonate a uranium device rather than plutonium, which is believed to have been used in its tests in 2006 and 2009.
To find out which bomb is used, "you have to be very lucky," Siegfried Hecker, former director of the Los Alamos National Laboratory in New Mexico now a professor at Stanford University in California, told the Times during a conference in Seoul.
Scientists said they must quickly detect and analyze the different types of xenon gases produced in an atomic explosion to distinguish between a bomb of plutonium or highly enriched uranium.
"The problem with xenon gases is that after 10 to 20 hours after the detonation, it gets extremely difficult to tell their ratio difference between a plutonium and atomic bomb," a nuclear scientist associated with the South Korean military said. "Since North Korea conducts its nuclear tests underground, it takes two to four days for the gases to get out, if they do at all. By then, it would be too late to tell the difference."
Hecker expressed similar concerns in a Foreign Policy magazine article.
"If a next test is well contained, then we may learn nothing about the device detonated," he wrote in the article posted on the magazine's website Tuesday. "However, one of the risks Pyongyang takes in trying to demonstrate a test at a higher level is that they may produce fissures that allow radioactive seepage or possibly cause a major blowout from the tunnel."