Alpha decay: Difference between revisions
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[[Alpha particle]]s have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the [[speed of light]]. There is surprisingly small variation around this energy, due to [[Geiger–Nuttall law|the strong dependence]] of the half-life of this process on the energy produced. Because of their relatively large mass, the electric charge of {{val|+2|u=e}} and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of [[air]]. | [[Alpha particle]]s have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the [[speed of light]]. There is surprisingly small variation around this energy, due to [[Geiger–Nuttall law|the strong dependence]] of the half-life of this process on the energy produced. Because of their relatively large mass, the electric charge of {{val|+2|u=e}} and relatively low velocity, alpha particles are very likely to interact with other atoms and lose their energy, and their forward motion can be stopped by a few centimeters of [[air]]. | ||
Approximately 99% of the [[helium]] produced on [[Earth]] is the result of the alpha decay of underground deposits of [[mineral]]s containing [[uranium]] or [[thorium]]. The helium is brought to the surface as a by-product of [[natural gas]] production. | Approximately 99% of the [[helium]] produced on [[Earth]] is the result of the alpha decay of underground deposits of [[mineral]]s containing [[uranium]] or [[thorium]].{{According to whom|date=October 2025}} The helium is brought to the surface as a by-product of [[natural gas]] production. | ||
== History == | == History == | ||
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|bibcode = 1928Natur.122..439G |doi-access=free | |bibcode = 1928Natur.122..439G |doi-access=free | ||
}}</ref> was hailed as a very striking confirmation of quantum theory. Essentially, the alpha particle escapes from the nucleus not by acquiring enough energy to pass over the wall confining it, but by tunneling through the wall. Gurney and Condon made the following observation in their paper on it: | }}</ref> was hailed as a very striking confirmation of quantum theory. Essentially, the alpha particle escapes from the nucleus not by acquiring enough energy to pass over the wall confining it, but by tunneling through the wall. Gurney and Condon made the following observation in their paper on it: | ||
<blockquote>It has hitherto been necessary to postulate some special arbitrary | <blockquote>It has hitherto been necessary to postulate some special arbitrary "instability" of the nucleus, but in the following note, it is pointed out that disintegration is a natural consequence of the laws of quantum mechanics without any special hypothesis... Much has been written of the explosive violence with which the α-particle is hurled from its place in the nucleus. But from the process pictured above, one would rather say that the α-particle almost slips away unnoticed.<ref name="gurney-Condon"/></blockquote> | ||
The theory supposes that the alpha particle can be considered an independent particle within a nucleus, that is in constant motion but held within the nucleus by strong interaction. At each collision with the repulsive potential barrier of the electromagnetic force, there is a small non-zero probability that it will tunnel its way out. An alpha particle with a speed of 1.5×10<sup>7</sup> m/s within a nuclear diameter of approximately 10<sup>−14</sup> m will collide with the barrier more than 10<sup>21</sup> times per second. However, if the probability of escape at each collision is very small, the half-life of the radioisotope will be very long, since it is the time required for the total probability of escape to reach 50%. As an extreme example, the half-life of the isotope [[bismuth-209]] is {{val|2.01|e=19|u=years}}. | The theory supposes that the alpha particle can be considered an independent particle within a nucleus, that is in constant motion but held within the nucleus by strong interaction. At each collision with the repulsive potential barrier of the electromagnetic force, there is a small non-zero probability that it will tunnel its way out. An alpha particle with a speed of 1.5×10<sup>7</sup> m/s within a nuclear diameter of approximately 10<sup>−14</sup> m will collide with the barrier more than 10<sup>21</sup> times per second. However, if the probability of escape at each collision is very small, the half-life of the radioisotope will be very long, since it is the time required for the total probability of escape to reach 50%. As an extreme example, the half-life of the isotope [[bismuth-209]] is {{val|2.01|e=19|u=years}}. | ||
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== Uses == | == Uses == | ||
[[ | [[Alpha emitter]]s are used in [[smoke detector]]s. The alpha particles [[ionize]] air in an open [[ion chamber]] and a small [[Electric current|current]] flows through the ionized air. Smoke particles from the fire that enter the chamber reduce the current, triggering the smoke detector's alarm.<ref>{{Cite web |title=Ionization vs photoelectric |url=https://www.nfpa.org/education-and-research/home-fire-safety/smoke-alarms/ionization-vs-photoelectric |access-date=2025-08-06 |website=www.nfpa.org |language=en}}</ref> | ||
[[Radium-223]] is also an [[alpha emitter]]. | [[Radium-223]] is also an [[alpha emitter]]. Its use has been trialed with successful results in treating [[bone metastasis]] resulting from [[Castration-resistant metastatic prostate cancer]].<ref>{{Cite journal |last1=Gupta |first1=Nishant |last2=Devgan |first2=Arushi |last3=Bansal |first3=Itisha |last4=Olsavsky |first4=Thomas D. |last5=Li |first5=Shuo |last6=Abdelbaki |first6=Ahmed |last7=Kumar |first7=Yogesh |date=October 2017 |title=Usefulness of radium-223 in patients with bone metastases |journal=Proceedings (Baylor University. Medical Center) |volume=30 |issue=4 |pages=424–426 |doi=10.1080/08998280.2017.11930213 |issn=0899-8280 |pmc=5595381 |pmid=28966451}}</ref> | ||
Alpha decay can provide a safe power source for [[radioisotope thermoelectric generator]]s used for [[space probe]]s<ref>{{cite web |url=http://solarsystem.nasa.gov/rps/rtg.cfm |archive-url=https://web.archive.org/web/20120807005925/http://solarsystem.nasa.gov/rps/rtg.cfm |url-status=dead |archive-date=7 August 2012 |title=Radioisotope Thermoelectric Generator |work=Solar System Exploration |publisher=[[NASA]] |access-date=25 March 2013}}</ref> and were used for [[Artificial pacemaker|artificial heart pacemakers]].<ref>{{cite web |url=http://osrp.lanl.gov/pacemakers.shtml |title=Nuclear-Powered Cardiac Pacemakers |work=Off-Site Source Recovery Project |publisher=[[LANL]] |access-date=25 March 2013}}</ref> Alpha decay is much more easily shielded against than other forms of radioactive decay.{{ | Alpha decay can provide a safe power source for [[radioisotope thermoelectric generator]]s used for [[space probe]]s<ref>{{cite web |url=http://solarsystem.nasa.gov/rps/rtg.cfm |archive-url=https://web.archive.org/web/20120807005925/http://solarsystem.nasa.gov/rps/rtg.cfm |url-status=dead |archive-date=7 August 2012 |title=Radioisotope Thermoelectric Generator |work=Solar System Exploration |publisher=[[NASA]] |access-date=25 March 2013}}</ref> and were used for [[Artificial pacemaker|artificial heart pacemakers]].<ref>{{cite web |url=http://osrp.lanl.gov/pacemakers.shtml |title=Nuclear-Powered Cardiac Pacemakers |work=Off-Site Source Recovery Project |publisher=[[LANL]] |access-date=25 March 2013}}</ref> Alpha decay is much more easily shielded against than other forms of radioactive decay.<ref name="BBC Bitesize">{{cite web |title=Types of radiation – Nuclear radiation – National 5 Physics Revision – BBC Bitesize |url=https://www.bbc.co.uk/bitesize/guides/zt9s2nb/revision/3 |website=BBC Bitesize |accessdate=14 August 2025}}</ref> | ||
[[Static eliminator]]s typically use [[polonium-210]], an alpha emitter, to ionize the air, allowing the "static cling" to dissipate more rapidly.{{ | [[Static eliminator]]s typically use [[polonium-210]], an alpha emitter, to ionize the air, allowing the "static cling" to dissipate more rapidly.<ref>{{cite web |title=Static Eliminators (1960s and 1980s) |url=https://www.orau.org/health-physics-museum/collection/consumer/miscellaneous/static-eliminators.html |website=Museum of Radiation and Radioactivity |publisher=Oak Ridge Associated Universities |access-date=26 October 2025 |language=en}}</ref> | ||
== Toxicity == | == Toxicity == | ||
Highly charged and heavy, alpha particles lose their several [[MeV]] of energy within a small volume of material, along with a very short [[mean free path]]. This increases the chance of [[double-strand break]]s to the DNA in cases of internal contamination, when ingested, inhaled, injected or introduced through the skin. Otherwise, touching an alpha source is typically not harmful, as alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells that make up the [[epidermis]]; however, many alpha | Highly charged and heavy, alpha particles lose their several [[MeV]] of energy within a small volume of material, along with a very short [[mean free path]]. This increases the chance of [[double-strand break]]s to the DNA in cases of internal contamination, when ingested, inhaled, injected or introduced through the skin. Otherwise, touching an alpha source is typically not harmful, as alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells that make up the [[epidermis]]; however, the [[decay chain]] of many alpha emitting isotopes, for example [[Radium 226]], contain daughter nuclei that undergo [[beta decay|beta]]- and/or [[gamma decay|gamma]]-decay.<ref>{{cite web |title=Radium-226 Decay Chain |url=https://www.nist.gov/image-23773 |website=NIST |access-date=26 October 2025 |language=en}}</ref> | ||
[[Relative biological effectiveness]] (RBE) quantifies the ability of radiation to cause certain biological effects, notably either [[cancer]] or [[necrosis|cell-death]], for equivalent radiation exposure. Alpha radiation has a high [[linear energy transfer]] (LET) coefficient, which is about one ionization of a molecule/atom for every [[angstrom]] of travel by the alpha particle. The RBE has been set at the value of 20 for alpha radiation by various government regulations. The RBE is set at 10 for [[neutron]] irradiation, and at 1 for [[Beta decay|beta radiation]] and ionizing photons. | [[Relative biological effectiveness]] (RBE) quantifies the ability of radiation to cause certain biological effects, notably either [[cancer]] or [[necrosis|cell-death]], for equivalent radiation exposure. Alpha radiation has a high [[linear energy transfer]] (LET) coefficient, which is about one ionization of a molecule/atom for every [[angstrom]] of travel by the alpha particle. The RBE has been set at the value of 20 for alpha radiation by various government regulations. The RBE is set at 10 for [[neutron]] irradiation, and at 1 for [[Beta decay|beta radiation]] and ionizing photons. | ||
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== External links == | == External links == | ||
* [[Image:Ndslivechart.png]] '''[http://www-nds.iaea.org/livechart The LIVEChart of Nuclides | * [[Image:Ndslivechart.png]] '''[http://www-nds.iaea.org/livechart The LIVEChart of Nuclides – IAEA ]''' with filter on alpha decay | ||
* [http://nagysandor.eu/AsimovTeka/AlphaExamples/index_en.html Alpha decay with 3 animated examples] showing the recoil of daughter | * [http://nagysandor.eu/AsimovTeka/AlphaExamples/index_en.html Alpha decay with 3 animated examples] showing the recoil of daughter | ||
== See also == | == See also == | ||
* [[Beta decay]] | * [[Beta decay]] | ||
* [[Gamma decay]] | * [[Gamma decay]] | ||
* [[ List | * [[List of alpha-emitting nuclides ]] | ||
{{Nuclear processes}} | {{Nuclear processes}} | ||