Tuesday, November 7, 2006
Many physicists suspect that North Korea's recent nuclear test was what weapons designers used to call a fizzle.
There was a nuclear chain reaction and enough energy was released to send seismic waves from one end of the planet to the other. Even more would have been generated, but the device probably blew itself apart too fast.
This is not totally surprising, because making a workable atomic bomb is not easy. Thank goodness.
The idea is to take a sphere of pure plutonium-239 and compress it into a solid, super-critical ball. Then neutrons split nuclei, which emit more neutrons, which split more nuclei, and the chain reaction proceeds exponentially.
The smaller nuclei have extra binding energy, which they shed as gamma rays, x-rays, and a tremendous explosion.
However, the sphere must be compressed precisely and rapidly. Generally, the sphere is surrounded by carefully shaped conventional explosives. All of these charges have to be detonated at essentially the same instant. Not easy.
Circuitry originally depended on ultra-high speed switches called klystrons. Until a few days ago people interested in the details could find them online in old Iraqi military papers posted by the U.S. government for some strange reason.
When the Web existence of the atomic secrets became known they were quickly taken down.
The whole episode is bizarre.
The principles of atomic weapons are well known and the subject of many books. The difficulties lie in the details, like, how do you rig the explosives.
Once that gets out, assuming it hasn't already courtesy of the U.S., the world will be in a heap of trouble.