In the first reports released since North Korea announced its nuclear test, Chinese officials and Americans said they found in the air above the test site, evidence of a nuclear explosion. But in the last report, a U.S. official said that scientists have found preliminary evidence of a nuclear explosion.
Even the experts did not detect airborne particles that typically result from a nuclear incident, that does not mean that no nuclear explosion has occurred. This lack of evidence can mean several things:
* No nuclear explosion occurred;
* A nuclear explosion occurred, but was exceptionally small and / or has not been fully successful;
* The underground blast was completely contained (a pretty unlikely event);
* The blast was not completely contained, but the testing was done before the underground crater collapsed to form an opening in the surface of the test site, releasing radioactive particles into the atmosphere.
On October 10, 2006, a day after the disclosure of the test, the United States sent an aircraft “sniffer” to check the skies of North Korea in search of radiological evidence of a nuclear event. The plane that performs this task is the Constant Phoenix WC-135, an “atmospheric collection aircraft”, which performs regular patrols to ensure the Treaty of Limited Nuclear Test Ban of 1963. According to Air Force U.S., this airplane has sniffer “devices outflow to collect particles on a filter paper and a compressor system for whole air samples collected in holding spheres. The plane’s technology includes analysis equipment that provides results in real time, so if radioactive particles are present in the air, it is discovered immediately, so the plane flies over a specific location.
So what exactly is the WC-135 for in its atmospheric testing? It checks for ionizing radiation – radioactive isotopes, specifically several isotopes of xenon, characteristic only in nuclear events. They are produced in the act of nuclear detonation, resulting from fission that produces the explosion (see How Nuclear Bombs). Not only are atmospheric explosions that create the fallout: the nuclear tests conducted underground and under water almost always release these particles in the air. A nuclear blast is completely contained a rare event (see Is it possible to test a nuclear weapon without producing radioactive fallout?).
Although atmospheric testing can not pinpoint the exact location of a nuclear explosion, it can declare that the explosion actually occurred is in the index characteristic of xenon isotopes in the atmosphere. This finding is considered an absolute nuclear signature.
Another method to detect a nuclear explosion is by means of a seismograph, a device that monitors the tremors of the earth to pinpoint and analyze earthquake activity (among other tremors of the ground). Indeed, there is an entire network of 500 seismograph stations deployed around the world who have the job of recording incidents that make the ground tremble, and this includes any evidence of bomb blasts. The article “Detecting Underground Nuclear Blasts,” NPR reports that the seismic activity recorded on October 09 2006 stated a ground disturbance that would be equivalent to an earthquake of magnitude 4.2. This magnitude indicates an explosion of about 1 kiloton, equivalent to the power of a thousand tons of TNT.
Find out if a seismic event is an earthquake or an explosion is relatively simple. Scientists perform analysis of wave patterns, which can confirm exactly what happened. Quite simply, in an earthquake, the ground begins to shake slowly as the plates collide against each other, and then the seismic activity increases when the ground really starts to move. In an explosion, the initial burst is extremely powerful. Then, the movement of soil is becoming weaker. Find out if what happened was an explosion and not an earthquake, however, is only part of the process, as seismographs can not determine the nature if the explosion was nuclear or conventional. Furthermore, it is possible to “hide” a nuclear explosion by detonating it, for example, in a large underground cavity. This reduces the effects on the ground because all the gas released by the explosion is confined in the gaping hole. These limitations of the seismograph make atmospheric testing is a necessary component in the detection system.
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