Other Definitions
spallation (dict)
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SpallationIn nuclear physics, spallation is the process in which a heavy nucleus emits a large number of nucleons as a result of being hit by a high-energy proton, thus greatly reducing its atomic weight. Spallation occurs naturally in earth's atmosphere owing to the impacts of cosmic rays, and also on the surfaces of bodies in space such as meteors and the moon. Evidence of cosmic ray spallation is evidence that the material in question has been exposed on the surface of the body of which it is part, and gives a means of measuring the length of time of exposure. Cosmogenic isotopes of aluminium, beryllium, chlorine, iodine and neon, formed in this manner, have been detected on earth. Spallation is one of the processes by which a particle accelerator may be used to produce a beam of neutrons. A mercury target is used, and 20 to 30 neutrons are expelled after each impact. Although this is a far more expensive way of producing neutron beams than by a chain reaction of nuclear fission in a nuclear reactor, it has the advantage that the beam can be pulsed with relative ease. External links
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