Alpha decay

From Free net encyclopedia

Template:Nuclear processes Alpha decay is a form of radioactive decay in which an atomic nucleus ejects an alpha particle through the electromagnetic force and transforms into a nucleus with mass number 4 less and atomic number 2 less. For example:

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{}^2{}^{38}_{92}\hbox{U}\;\to\;{}^2{}^{34}_{90}\hbox{Th}\;+\;{}^4_2\hbox{He}^{2+}, </math> although this is usually written as:

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{}^{238}\hbox{U}\;\to\;^{234}\hbox{Th}\;+\;\alpha. </math> Note that an alpha particle is a helium nucleus, and that both mass number and atomic number are conserved. Alpha decay can essentially be thought of as nuclear fission where the parent nucleus splits into two daughter nuclei. Alpha decay is fundamentally a quantum tunneling process. Unlike beta decay, alpha decay is governed by the strong nuclear force.

Alpha particles with their typical kinetic energy of 5 MeV (that is ≈0.13% of their total energy, i.e. 110 TJ/kg), have a speed of 15,000 km/s.

Because of alpha decay, virtually all of the helium produced in the United States and elsewhere comes from trapped underground deposits associated with minerals containing uranium or thorium, and brought to the surface as a by-product of natural gas production.

Alpha particles emitted by radioactive nuclei are among the most hazardous forms of radiation, if these nuclei are incorporated within a human body. As any heavy charged particle, alpha particles lose their energy within a very short distance in dense media, causing significant damage to surrounding biomolecules. On the other hand, external alpha irradiation is not harmful because alpha particles are completely absorbed by a very thin (micrometers) dead layer of skin as well as by few centimeters of air. However, if a substance radiating alpha particles is ingested or inhaled by (or injected into) an organism it may become a risk, potentially inflicting very serious damage to the organisms' genetic makeup.de:Alphazerfall fr:Radioactivité α ko:알파 붕괴 is:Alfasundrun it:Decadimento alfa he:קרינת אלפא hu:Alfa-részecske ja:アルファ崩壊 pl:Rozpad alfa ru:Альфа-распад sl:Razpad alfa sv:Alfasönderfall zh:Α衰变