No clear danger from Korean bomb fizzle

By Li Xiguang

Global Times, January 25, 2011

[By Liu Rui/Global Times ]

In the summer of 1946, under a tree outside a Yan'an cave in Shaanxi Province, Mao Zedong told US journalist Anna Louise Strong, "The atomic bomb is a paper tiger which the US reactionaries use to scare people. It looks terrible, but in fact it isn't."

Some 65 years later, is the threat of the North Korean nuclear bomb just a paper tiger?

In a warm classroom at Tsinghua University, 83-year-old He Zuoxiu, one of the leading scientists to design China's first hydrogen bomb in 1960s, lectured journalism students on how scientific judgment is more important than news judgment.

He used the North Korean nuclear case to illustrate his point. "The US nuclear scientists know that North Korea does not have an atomic bomb," He claims, "The North Korean bomb exists only in newspapers."

He wrote two equations on a white board:

n+U235 fission+2.5n

n+Pu239 fission+2.9n

"This is the basic principle of an atomic bomb," He explained. "The key to make a successful atomic bomb is to assemble a mass of fissile material into a supercritical mass to start an exponentially growing nuclear chain reaction."

"When a free neutron strikes the nucleus of an atom of material like uranium 235 or plutonium 239, the nucleus is split into two smaller fragments," the white-haired academician continued, "Energy is released when those neutrons split off from the nucleus, and the newly released neutrons strike other uranium 235 or plutonium 239 nuclei, releasing more energy and more neutrons, creating instant chain reaction."

"The key is how to control the reaction. But North Korean scientists failed to do so in their tests," He asserted.

When North Korea set off its first two bombs in 2006 and 2009, some doubted that they were real devices, and proposed that they could be gas or chemical explosions, or simply fake bombs.