North Korea has exploded another nuclear device 鈥� and it could be a game-changer.
In an announcement earlier today, the state a 鈥渉ydrogen bomb鈥� that had been 鈥渕iniaturised鈥�.
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Nuclear experts say it is unlikely to have been what is normally called an H-bomb, the thermonuclear mainstay of nuclear arsenals in the US, Russia and China. But the term could reveal something else that uses hydrogen, and could be much more worrying: an ordinary nuclear bomb, small enough for North Korea to mount 鈥� and deliver 鈥� on a missile.
A seismic event was detected at 01:30 Greenwich Mean Time by the global network of seismographs intended to verify the Comprehensive Nuclear Test Ban Treaty (CTBT) outlawing nuclear explosions. Although non-ratification by the US and others means the treaty is not yet in force, the network is operational and has picked up other underground tests.
Unusual event
The CTBT鈥檚 technical office in Vienna that 鈥淥ur monitoring stations picked up an unusual seismic event鈥� The location is very similar to the event our system registered on 12 February 2013,鈥� when North Korea last conducted a nuclear test.
That was confirmed by Franz Ossing at the German Geological Research Centre in Potsdam, who says that the depth, geographical location and waveform of the event were identical to previous North Korean tests, making it very unlikely to be an earthquake.
But its makes it unlikely to have been a hydrogen bomb. The first nuclear bombs employed simple chain reactions involving enriched uranium or plutonium. In hydrogen bombs, developed in the US and Russia in the 1950s, the first fission reaction triggers a second fusion reaction with a hundred to a thousand times as much force.
Today鈥檚 explosion caused a seismic shiver only a bit more powerful than the last test, estimated at equal to 10聽kilotonnes of TNT. The bomb dropped on Hiroshima was 15 kT. A proper hydrogen bomb should be much bigger.
Intensified explosion
But the blast is compatible with 鈥渂oosted fission鈥�, a standard fission weapon spiked with heavy isotopes of hydrogen, or with lithium. These emit neutrons during the initial fission reaction, which trigger limited nuclear fusion reactions, intensifying the resulting explosion.
This allows a bomb designer to dispense with some of the heavy hardware normally needed to coax a mass of enriched uranium or plutonium into a chain reaction. The trick was tested by the US, Russia and China, and even South Africa, in the early days of their nuclear programmes as a means of miniaturising warheads.
鈥淣orth Korea may have tested aspects of such a one-stage design, namely the ignition of the thermonuclear material in a predominately fission nuclear explosion,鈥� says of the Institute for Science and International Security, a think tank in Washington DC that monitors nuclear activities.
In 2010, North Korea even announced it had done experiments with 鈥渇usion鈥�. The claims were dismissed, partly because seismologists saw no large explosion. But the CTBT鈥檚 worldwide network of detectors for airborne radionuclides picked up xenon and other elements in air from North Korea consistent with 鈥渉ydronuclear鈥� tests of hydrogen-boosted fission in a device that wasn鈥檛 meant to produce a fullnuclear explosion.
Hydrogen boost
Last September, that North Korea had installed equipment to produce and isolate heavy hydrogen, although using it in a bomb would require full underground tests.
That could be what happened today. The South Korean that a hydrogen-boosted fission weapon is what North Korea means by 鈥渉ydrogen bomb鈥�. Such a weapon, 鈥渃an be miniaturised, which is a considerable advantage鈥�, the agency notes.
There is no point building a big bomb if you can鈥檛 deliver it. Jeffrey Lewis of the Middlebury Institute of International Studies in Monterey, California that North Korea is focused on developing a bomb it can mount on its ever-increasing range of missiles.
Lewis, who favours resumption of long-stalled nuclear disarmament talks with North Korea, observed that while North Korea鈥檚 bombs are not nearly as big as genuine H-bombs, 鈥測ou really wouldn鈥檛 want this dropped in your neighbourhood鈥�.
Image credit: Chung Sung-Jun/Getty
