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Encyclopedia > Spallation

In general, spallation is a process in which fragments of material are ejected from a body due to impact or stress. In nuclear physics, it 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. In the context of impact physics it describes ejection or vaporization of material from a target during impact by a projectile. In planetary physics, spallation describes meteoritic impacts on a planetary surface and the effects of a stellar wind on a planetary atmosphere. In the context of mining or geology, spallation can refer to pieces of rock breaking off a rock face due to the internal stresses in the rock; it commonly occurs on mine shaft walls. In the context of anthropology, spallation is a process used to make stone tools such as arrowheads by knapping. Nuclear physics is the branch of physics concerned with the nucleus of the atom. ... In physics a nucleon is a collective name for two baryons: the neutron and the proton. ... // Properties [1][2] In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... ... A projectile is any object sent through space by the application of a force. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ... This article is about mineral extraction. ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Shaft mining is a type of underground mining done by use of a mine shaft. ... Anthropology is the study of the anatomical and mental composition of humanity through the examination of historical and present geographical distribution, cultural history, acculturation, cultural relationships, and racial classifications. ... American Indian arrowheads of several shapes and functions Japanese arrowheads of several shapes and functions Arrowhead can refer to: the point of an arrow; some plants in the genus Sagittaria; the Arrowhead region of northeastern Minnesota; a place name in southern California, derived from an arrowhead-shaped geologic formation in... A flintknapper is an individual who shapes flint or other stone through the process of knapping or lithic reduction, to manufacture stone tools, strikers for flintlock firearms, or to produce flat-faced stones for building or facing walls. ...

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Nuclear spallation

See also Cosmic ray spallation Cosmic ray spallation is a form of naturally occuring nuclear fission and nucleosynthesis. ...


Nuclear 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 meteorites 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. The composition of the cosmic rays themselves also indicates that they have suffered spallation before reaching Earth, because the proportion of light elements such as Li, B,and Be in them exceeds average cosmic abundances; these elements in the cosmic rays were evidently formed from spallation of Oxygen, Nitrogen, Carbon and perhaps Silicon in the cosmic ray sources or during their lengthy travel here. Cosmogenic isotopes of aluminium, beryllium, chlorine, iodine and neon, formed by spallation of terrestrial elements under cosmic ray bombardment, have been detected on earth. Layers of Atmosphere - not to scale (NOAA)[2] Earths atmosphere is a layer of gases surrounding the planet Earth and retained by the Earths gravity. ... Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... Willamette Meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earths surface without being destroyed. ... Apparent magnitude: up to -12. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number beryllium, Be, 4 Chemical series alkaline earth metals Group, Period, Block 2, 2, s Appearance white-gray metallic Atomic mass 9. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Atomic mass 126. ... General Name, Symbol, Number neon, Ne, 10 Chemical series noble gases Group, Period, Block 18, 2, p Appearance colorless Atomic mass 20. ...


Nuclear spallation is one of the processes by which a particle accelerator may be used to produce a beam of neutrons. A mercury, tantalum or other heavy metal 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. The concept of nuclear spallation was first coined by Nobelist Glenn T. Seaborg in his doctoral thesis on the inelastic scattering of neutrons in 1937.[1] A 1960s single stage 2 MeV linear Van de Graaff accelerator, here opened for maintenance A particle accelerator is a device that uses electric fields to propel electrically charged particles to high speeds and magnetic fields to contain them. ... ≈≈ This article or section does not cite its references or sources. ... General Name, Symbol, Number mercury, Hg, 80 Chemical series transition metals Group, Period, Block 12, 6, d Appearance silvery Atomic mass 200. ... General Name, Symbol, Number tantalum, Ta, 73 Chemical series transition metals Group, Period, Block 5, 6, d Appearance gray blue Atomic mass 180. ... A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions. ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ... Core of a small nuclear reactor used for research. ... Glenn T. Seaborg Glenn Theodore Seaborg (April 19, 1912 – February 25, 1999) was an American chemist prominent in the discovery and isolation of ten transuranic elements including plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium and seaborgium, which was named in his honor. ...


Laser spallation

Laser induced spallation is a recent experimental technique developed to understand the adhesion of thin films with substrates. A high energy pulsed laser (typically Nd:YAG) is used to create a compressive stress pulse in the substrate wherein it propagates and reflects of as a tensile wave at the free boundary. This tensile pulse spalls/peels the thin film while propagating towards the substrate. Using theory of wave propagation in solids it is possible to extract the interface strength. The stress pulse created in this fashion is usually around 3-8 nanoseconds in duration while its magnitude varies as a function of laser fluence. Due to the non-contact application of load, this technique is very well suited to spall ultra-thin films (1 micron in thickness or less). It is also possible to mode convert a longitudinal stress wave into a shear stress using a pulse shaping prism and achieve shear spallation. Dew drops adhering to a spider web Adhesion is the molecular attraction exerted between bodies in contact. ... Thin films are thin material layers ranging from fractions of a nanometre to several micrometres in thickness. ... An etched silicon wafer In microelectronics, a wafer is a thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are constructed by doping (for example, diffusion or ion implantation), etching, and deposition of various materials. ... For other uses, see Laser (disambiguation). ... Compressive stress is the stress applied to materials resulting in their compaction (decrease of volume). ... An etched silicon wafer In microelectronics, a wafer is a thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are constructed by doping (for example, diffusion or ion implantation), etching, and deposition of various materials. ... Wave propagation refers to the ways waves travel through a medium (waveguide). ... A nanosecond is an SI derived unit of time equal to 10-9 of a second. ... For other uses, see Laser (disambiguation). ... Thin films are thin material layers ranging from fractions of a nanometre to several micrometres in thickness. ... Shear stress is a stress state where the stress is parallel to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ... In physics and mechanics, shear refers to a deformation that causes parallel surfaces to slide past one another (as opposed to compression and tension, which cause parallel surfaces to move towards or away from one another). ...


Production of Neutrons at a Spallation Neutron Source

Generally the production of neutrons at a spallation source begins with a high powered accelerator. This is more often than not a synchrotron. As an example, the ISIS Neutron source is based on some components of the former Nimrod synchrotron. Nimrod was uncompetitive for high energy physics so it was replaced with a new synchrotron, initially using the original injectors, but which produces a highly intense pulsed beam of protons. Whereas Nimrod would produce around 2ųA at 7GeV, ISIS produces 200 ųA at 800 MeV. This is pulsed at the rate of 50 Hz, and this intense beam of protons is focused onto a target. Experiments have been done with depleted uranium targets but although these produce the most intense neutron beams, they also have the shortest lives. Generally, therefore, tantalum targets have been used. Spallation processes in the target produce the neutrons, initially at very high energies - a good fraction of the proton energy. These neutrons are then slowed in moderators filled with liquid hydrogen or liquid methane to the energies that are needed for the scattering instruments. Whilst protons can be focused since they have charge, chargeless neutrons cannot be, so in this arrangement the instruments are arranged around the moderators. Depleted uranium storage yard. ... General Name, Symbol, Number tantalum, Ta, 73 Chemical series transition metals Group, Period, Block 5, 6, d Appearance gray blue Atomic mass 180. ... LH2 is an acronym used in the aerospace industry, which stands for Liquid Hydrogen. ...


Reference

See also

April 2005 aerial photo of the SNS site, Oak Ridge, Tennessee, USA. The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built in Oak Ridge, Tennessee, USA, by the U.S. Department of Energy (DOE). ... ISIS experimental hall The ISIS facility is a scientific research institution, situated at the Rutherford Appleton Laboratory in Oxfordshire, UK. It contains a pulsed spallation neutron source, the most powerful in the world, which enables muon and neutron scattering science to probe the structure and properties of matter, from the...

External links


  Results from FactBites:
 
Spallation - Wikipedia, the free encyclopedia (221 words)
In 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 meteorites and the moon.
Spallation is one of the processes by which a particle accelerator may be used to produce a beam of neutrons.
  More results at FactBites »

 
 

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