Although North Korea's bombs were tested in a mountain cave, radioactive isotopes were detected by a US military aircraft. Seismic readings were also obtained at the nearby Chinese city of Dandong. "The blast was less than a kiloton," He said, "It was a fizzle."
By comparison, the first plutonium nuclear device tested by the US in 1945 yielded 20 kilotons. If the North Korean nuclear test is less than even a kiloton in yield, it could be classified as a "fizzle," indicating that some aspect of the bomb design or nuclear material production did not function correctly, He explained.
In his research, He also found that North Korea used impure plutonium 239 as fissile material mixed with some plutonium 230. "As a result, North Korea produced a dud."
On October 16, 1964, when a Chinese defense leader reported to Mao Zedong that China had successfully tested its first atomic bomb, Mao could not believe it and reportedly questioned, "Probably you are cheating me by exploding a huge pile of explosives." It was not until after Mao saw the scientific data measured by the top nuclear scientists that he allowed the official Xinhua News Agency to dispatch bulletins announcing China's successful test of the bomb, and a nationwide celebration was launched.
But after the nuclear tests, North Korean leaders hurriedly organized mass celebrations while the US lost no time in denouncing North Korea. The US and South Korea used North Korea's "nuclear paper tiger" as an excuse for carrying out large-scale military drills in the Yellow Sea, which included a nuclear-powered US aircraft carrier, and were viewed by China as a grave military provocation.
Pyongyang is certainly trying. US nuclear scientist Siegfried Hecker, who recently went to North Korea, says North Korea has secretly built a facility with 2,000 centrifuges to enrich uranium.
"Uranium enrichment would give the North a better way to make atomic bombs than its previous plutonium-based program," He commented.
"But with only 2,000 centrifuges, it will take the North at least 10 years to produce 30 to 50 kilograms of uranium 235 to make a real bomb."
The author is a professor of Tsinghua University. His blog: blog.sina.com.cn/lixiguang2010. xiguang@tsinghua.edu.cn