During the Cold War, there were several attempts to ban nuclear tests and the concept of having a Comprehensive Nuclear Test Ban Treaty (CTBT) came into existence. The idea, however, could not get wide acceptance as most of the developing world saw it as an attempt to divide the world into nuclear haves and nuclear have-nots. After the collapse of the Soviet Union, negotiations started in 1994 and it was realised that even the nuclear powers at the time the United States of America, Russia, China, France and the United Kingdom would not sign the treaty unless there was an international verification regime to monitor every nuclear explosion carried out anywhere in the world. The treaty is yet to become law as many countries, including India, Pakistan and North Korea, that have become nuclear powers now have not signed it. Perhaps the only visible role of the treaty in today’s world is the comprehensive verification regime that detects all nuclear explosions.
The verification regime of CTBT includes a global net work of stations designed to detect any nuclear explosion -underground, underwater or in the atmosphere. The main elements of this regime are the International Monitoring System (IMS), International Data Centre (IDC) and the global communication infrastructure.There are 321monitoring stations and 16 laboratories under the IMS to detect any sign of a nuclear explosion on the planet. The communication system includes a network of six satellites and several terrestrial links to send the data to the IDC.
There are four monitoring methodologies –seismic, hydroacoustic, infrasound and radionuclide monitoring. Underground nuclear testing started in the 1950s and it was soon recognised that seismic observations could be used to verify the location as well as the strength of tests. Earthquakes as well as manmade events like nuclear explosions or the use of explosives in mines generate seismic waves. The seismic monitoring system consists of 170 seismic stations -50 primary and 120 auxiliary . Pri mary stations work continuously and relay data to the IDC. Auxiliary stations provide data only on request.These waves travel so fast that events causing them can be located by seismic stations over a period ranging from a few seconds to about 10 minutes after the event.
A nuclear explosion done underwater or near the surface of the ocean gen erates sound waves that can be detected by the hydroacoustic monitoring system.The system uses technology that measures change in water pressure caused by the sound of the explosion. The network consists of 11 stations. Six of these hydro phone sensors are located in the oceans, while another five are located on steep sloped islands.
Nuclear explosions carried out in the atmosphere or at a shallow depth underground generate infrasound waves. Infrasound is acoustic waves with very low frequencies below the frequency audible to human ears. The typical audible frequency that the human ear can hear ranges between 20 to 20,000 Hertz. Infrasound is produced by nuclear explosions, volcanic eruptions, earthquakes, meteors and so on. The IMS infrasound network consists of 60 stations located in 35 countries.
When a nuclear explosion takes place, nearly 90% of the energy is released within minutes of the blast in the form of shockwaves and heat generated by the explosive energy . The remaining 10% of the energy is released slowly in the form of residual radiation through the process of radioactive decay of the fission products of which most are highly unstable. Shallow underground and underwater explosions can also release radiation in the atmosphere, though wellcontained nuclear explosions in water or underground don’t cause atmospheric radiation. This radiation as well as radioactive particles can travel several kilometres borne by the wind. There are 80 stations across the world to measure this, supported by 16 laboratories to analyse the samples.
Via Times of India.