NUCLEAR, BIOLOGICAL AND CHEMICAL WEAPONS
October 30, 2006: The recent nuclear weapons test in northeast Korea, revived interest in such arcane subjects as "partially successful" nuclear weapons, faking a nuclear explosion and arcane detection methods. The North Korean test showed up on earthquake detectors (seismographs) as a small (4.2 magnitude) quake. A few quick calculations revealed that this indicated an explosion of less than one kiloton (equal to 1,000 tons of conventional explosives). Since the North Koreans were using plutonium for their bomb, and the smallest plutonium bomb is (for technical reasons) at least twenty kilotons, this set of alarm bells. This indicated that the North Koreans were either faking it (with conventional explosives), or had a poorly built bomb that only partially went off.
Fortunately, there are ways to find out if such a large explosion is real or fake. A nuclear explosion, even a "fizzle" (a bomb that does not detonate all its nuclear material), will emit some unique chemicals into the atmosphere. This will happen even with an underground explosion, because the earth is full of cracks and crevices that allow some of the gasses to escape into the atmosphere. American recon aircraft, off the coast of North Korea, did indeed pick up the presence of unusually high levels of argon 37 and xenon 133. These two elements are present naturally in very small quantities. One of the things American recon aircraft do over the years, is check the natural levels of these rare elements. With this baseline, it's easy to see when a nuclear explosion has occurred nearby, because the normal levels of these two elements spike.
Having instruments that can detect minute quantities of rare elements has made it impossible to fake a nuclear test. And there have been some very large conventional explosions. In 1985, some 4.500 tons of ammonium nitrate and fuel oil (a "fertilizer bomb) was detonated by American researchers, to create an explosion similar to a nuclear one. Seismographs indicated that this explosion similar to what would be expected for an eight kiloton nuclear bomb. There have been similarly large explosions before, but always accidental. In 1947, a ship carrying 8,500 tons of ammonium nitrate exploded in a Texas port, destroying the surrounding area, and killing over 500 people. These large conventional explosions create the mushroom shaped cloud we associate with nuclear explosions. Such clouds are typical of any large explosion, nuclear or not. But unless certain types of radiation are present, you know the explosion is non-nuclear.
Poor bomb design, or low quality components, have caused fizzles in the past. In 1998, several of Pakistan's nuclear weapons tests failed in a similar fashion to the current North Korean one. It may be that design that was sold to North Korea by the Pakistani nuclear scientists that, at that time, were running an illegal nuclear weapons sales business on the side.