Nuclear detectionDetecting a North Korea nuclear test

Amid growing speculation that a North Korean nuclear test was imminent, the five permanent members of the UN Security Council urged the reclusive state to “refrain from further actions which may cause grave security concerns in the region, including any nuclear tests,” in a joint statement issued by the United States, Britain, France, Russia, and China.

North Korea has thus far run two nuclear tests, in 2006 and 2009, using plutonium as the weapon’s material. It is expected that this next test will use highly enriched uranium instead of plutonium.

According to Pakistan’s Daily Times, in 2007 the North stopped operating its plutonium-producing reactor at Yongbyon, as part of an international agreement which it later abandoned. Then in 2010, North Korea disclosed to a visiting group of U.S. scientists the existence of a uranium enrichment facility Yongbyon with 2,000 centrifuges. The scientists have said that the plant, which was supposed to be producing fuel for a light water reactor for power generation, could easily be reconfigured to produce weapon-grade uranium.

Satellite photos of the test site at Punggye-ri show working progress.

How, however, would the world know of the test, if it took place?

The monitoring tools that scientists have available to them have improved in quality and quantity since North Korea last tested a nuclear weapon in 2009, according to a Herald Sun report.

Seismic monitoring is the fastest, most effective way of detecting a nuclear explosion. Seismic waves travel at about five miles per second, and the closest monitoring stations are in Japan and South Korea.

The Comprehensive Test Ban Treaty Organization (CTBTO) has a total of 287 detection facilities available, consisting of 157 seismic monitoring stations, forty-five infrasound stations, sixty-five radionuclide stations, and ten hydroacoustic stations, in combination with labs.

Stations within the region of an explosion can detect yields as small as twenty tons, or 0.02 kilotons.

Radionuclide signals is an extremely sensitive technique that uses sensors to detect the products of an explosion that seep out of the ground or are released into the air. Atmospheric transport modeling is then applied to the data, which will approximate the point of origin and identify where the plume is headed. This technology is slower than some of the others, and is largely used as confirmation.

Infrasound waves, frequencies of .01 Hertz (cycles per second) to ten Hertz, are below the range of human hearing are typically produced by explosions in the atmosphere, though they may be produced by underground explosions. A very small infrasound signal was detected in the 2009 test.

Hydroacoustic technology can detect explosions in or near the water by detecting and tracking the movement of sound waves in the water column. These monitors are sensitive enough to detect an explosion smaller than one ton.

The U.S Air Force Technical Applications Center uses a WC-135 aircraft to fly to the location of a debris plume and gather particulate matter for laboratory analysis.

Satellites can detect optical flashes, electromagnetic pulse, and nuclear radiation.

The CTBTO provides technical data and event analysis, but does not pass judgment on whether an event is an earthquake, chemical blast, or nuclear explosion.

That determination is made by the individual countries, particularly those with the technical capabilities to make such judgments.