Beta particle
37872
223491462
2008-07-04T08:36:59Z
Luna Santin
1587622
Reverted edits by [[Special:Contributions/78.40.239.5|78.40.239.5]] ([[User talk:78.40.239.5|talk]]) to last version by VASANTH S.N.
[[Image:Alfa beta gamma radiation.svg|300px|thumb|Alpha radiation consists of [[helium]] nuclei and is readily stopped by a sheet of paper. Beta radiation, consisting of [[electron]]s, is halted by an aluminum plate. Gamma radiation is eventually absorbed as it penetrates a dense material.]]
'''Beta particles''' are high-energy, high-speed [[electron]]s or [[positron]]s emitted by certain types of [[radioactive]] [[Atomic nucleus|nuclei]] such as [[potassium]]-40. The beta particles emitted are a form of [[ionizing radiation]] also known as beta rays. The production of beta particles is termed [[beta decay]]. They are designated by the [[Greek alphabet|Greek letter]] beta (β).
There are two forms of beta decay, β<sup>−</sup> and β<sup>+</sup>, which respectively give rise to the [[electron]] and the [[positron]].
==β<sup>−</sup> decay (electron emission)==
{{main|Beta decay}}
[[Image:Beta-minus Decay.svg|thumb|Beta decay]]
An unstable atomic nucleus with an excess of [[neutron]]s may undergo [[beta decay|β<sup>−</sup> decay]], where a neutron is converted into a [[proton]], an [[electron]] and an [[electron antineutrino|electron-type antineutrino]] (the [[antiparticle]] of the [[neutrino]]):
:{{SubatomicParticle|neutron}} → {{SubatomicParticle|proton}} + {{SubatomicParticle|electron}} + {{SubatomicParticle|electron antineutrino}}
This process is mediated by the [[weak interaction]]. The neutron turns into a proton through the emission of a [[virtual particle|virtual]] [[weak interaction|W<sup>−</sup> boson]]. At the [[quark]] level, W<sup>−</sup> emission turns a down-type quark into an up-type quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark).
The virtual W<sup>−</sup> boson then decays into an electron and an antineutrino.
Beta decay commonly occurs among the neutron-rich fission byproducts produced in nuclear reactors. Free neutrons also decay via this process. This is the source of the copious amount of electron antineutrinos produced by fission reactors.
==β<sup>+</sup> decay (positron emission) ==
{{main|Beta decay}}
Unstable atomic nuclei with an excess of [[proton]]s may undergo [[beta decay|β<sup>+</sup> decay]], also called inverse beta decay, where a proton is converted into a [[neutron]], a [[positron]] and an electron-type [[neutrino]]:
:{{SubatomicParticle|proton}} → {{SubatomicParticle|neutron}} + {{SubatomicParticle|positron}} + {{SubatomicParticle|electron neutrino}}
Beta plus decay can only happen inside nuclei when the absolute value of the [[binding energy]] of the daughter nucleus is higher than that of the mother nucleus.
Inverse beta decay is one of the steps in [[nuclear fusion]] processes that produce energy inside stars.
==Interaction with other matter==
{{Expand-section|date=June 2008}}
Being composed of charged particles, beta radiation is more strongly ionising than gamma radiation.
When passing through matter, a beta particle is decelerated by electromagnetic interactions and may give off [[Bremsstrahlung]].
== Uses ==
Beta particles can be used to treat health conditions such as eye and bone cancer, and are also used as tracers. [[Strontium]]-90 is the material most commonly used to produce beta particles. Beta particles are also used in quality control to test the thickness of an item, such as paper, coming through a system of rollers. Some of the beta radiation is absorbed while passing through the product. If the product is made too thick or thin, a correspondingly different amount of radiation will be absorbed. A computer program monitoring the quality of the manufactured paper will then move the rollers to change the thickness of the final product.
Inverse beta decay of a [[radioactivity|radioactive]] [[Radioactive tracer|tracer]] [[isotope]] is the source of the positrons used in [[positron emission tomography]] (PET scan).
== History ==
[[Henri Becquerel]], while experimenting with [[fluorescence]], accidentally found out that [[Uranium]] exposed a black paper wrapped [[photographic]] plate with some unknown [[radiation]] that could not be turned off like [[X-ray]]s.
[[Ernest Rutherford]] continued these experiments and discovered two different kinds of radiation:
* [[alpha particles]] that did not show up on the Becquerel plates because they were easily absorbed by the black wrapping paper (actually just about any sheet of paper fully absorbs alpha particles)
* beta particles which are 100 times more penetrating that alpha particles.
He published his results in 1899.
== Health ==
Beta particles are able to penetrate living matter to a certain extent (radiation intensity from a small source of radioactive material decreases as one over the distance squared) and can change the structure of struck molecules. In most cases such change can be considered as damage with results possibly as severe as cancer and death. If the struck molecule is [[DNA]] it can show a spontaneous [[mutation]]. If this mutated DNA is in [[gametes]] the mutation may be passed to new generations. Although by far most mutations are considered genetic defects, [[evolution]] is based on the principle that occasionally a mutation will prove useful to an organism which develops from a mutated gamete and that this beneficial mutation is likely to be passed on to that organism's descendents.<ref>{{cite journal |author=Aminetzach YT, Macpherson JM, Petrov DA |title=Pesticide resistance via transposition-mediated adaptive gene truncation in Drosophila |journal=Science |volume=309 |issue=5735 |pages=764–67 |year=2005 |pmid=16051794 |doi=10.1126/science.1112699}}</ref>
Beta sources can be used in [[radiation therapy]] to kill cancer cells.
== Future use ==
Some sources claim that [[betavoltaics|betavoltaic cells]] will be available in the near future to supply power to laptops and mobile phones without recharging for the expected useful life of the product. Since such cells use materials undergoing decay their power output is limited to its [[half-life]] related to the device's power needs. For example [[tritium]] has a half life of approximately 12 years, meaning after that span of time a cell powered by this [[isotope]] would produce half the power it did when assembled assuring that at some point the betavoltaic cell would die without more tritium.{{Fact|date=June 2008}}
==See also==
*[[Electron]]
*[[Electron irradiation]]
*[[Particle physics]]
*[[Alpha particles|α (alpha) particles]]
*Rays:
**[[gamma ray|γ (gamma) rays]]
**[[neutron radiation|n (neutron) rays]]
**[[delta ray|δ (delta) rays]]
**[[epsilon ray|ε (epsilon) rays]]
== References ==
*http://www.oasisllc.com/abgx/radioactivity.htm
*http://galileo.phys.virginia.edu/classes/252/rays_and_particles.html
*http://www.physics.isu.edu/radinf/hist.htm
*http://www.nextenergynews.com/news1/next-energy-news-betavoltaic-10.1.html
*http://community.zdnet.co.uk/blog/0,1000000567,10006069o-2000331777b,00.htm
[[Category:radiation]]
[[Category:Radioactivity]]
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