Alpha decay

2 less. For example:(The second form is preferred because the first form appears electrically unbalanced. Fundamentally, the recoiling nucleus is very quickly stripped of two electrons to neutralize the ionized helium cation.)

An alpha particle is the same as a helium-4 nucleus, and both mass number and atomic number are the same.Alpha decay is a form of nuclear fission where the parent atom splits into two daughter products. Alpha decay is fundamentally a quantum tunneling process. Unlike beta decay, alpha decay is governed by the weak nuclear force.

Alpha particles have a typical kinetic energy of 5 MeV (that is ≈0.13% of their total energy, i.e. 110 TJ/kg) and a speed of 15,000 km/s. This corresponds to a speed of around 0.05c. Because of their relatively large mass, +2 charge and relatively low velocity, they are very likely to interact with other atoms and lose their energy, so their forward motion is effectively stopped within a few centimeters of air.

Most of the helium produced on Earth comes from the alpha decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production.


By 1928, George Gamow had solved the theory of the alpha decay via tunneling. The alpha particle is trapped in a potential well by the nucleus. Classically, it is forbidden to escape, but according to the then newly discovered principles of quantum mechanics, it has a tiny (but non-zero) probability of "tunneling" through the barrier and appearing on the other side to escape the nucleus.


Americium-241, an alpha-emitter, is used in smoke detectors. The alpha particles ionize air between a small gap. A small current is passed through that ionized air. Smoke particles from fire that enter the air gap reduce the current flow, sounding the alarm.

Alpha decay can provide a safe power source for radioisotope thermoelectric generators used for space probes and artificial heart pacemakers. Alpha decay is much more easily shielded against than other forms of radioactive decay. Plutonium-238, for example, requires only 2.5 mm of lead shielding to protect against unwanted radiation.

Static Eliminators typically use Polonium-210, an alpha emitter, to ionize air, allowing the 'static cling' to more rapidly dissipate.


Being relatively heavy and positively charged, alpha particles tend to have a very short mean free path, and quickly lose kinetic energy within a short distance of their source. This results in several MeV being deposited in a relatively small volume of material. This increases the chance of cellular damage in cases of internal contamination. In general, external alpha radiation is not harmful since alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells. Even touching an alpha source is usually not harmful, though many alpha sources also are accompanied by beta-emitting radiodaughters, and alpha emission is also accompanied by gamma photon emission. If substances emitting alpha particles are ingested, inhaled, injected or introduced through the skin, then it could result in a measurable dose.

The Relative Biological Effectiveness (RBE) is a measure of the fact that alpha radiation is more effective at causing certain biological effects, notably either cancer or cell-death, compared to photon or beta radiation, for equivalent radiation exposure. This is generally attributable to the high Linear Energy Transfer (LET), which is about one ionization of a chemical bond 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 and ionizing photon radiation.

However, another component of alpha radiation is the recoil of the parent nucleus, due to the conservation of momentum requiring the parent nucleus to recoil, much like the 'kick' of a rifle butt when a bullet goes in the opposite direction. This gives a significant amount of energy to the recoil nucleus, which also causes ionizaton damage. The total energy of the recoil nucleus is readily calculable, and is roughly the weight of the alpha (4 amu) divided by the weight of the parent (typically about 200 amu) times the total energy of the alpha. By some estimates, this might account for most of the internal radiation damage, as the recoil nuclei are typically heavy metals which preferentially collect on the chromosomes. In some studies [Winters-TH, Franza-JR, Radioactivity in Cigarette Smoke, New England Journal of Medicine, 1982; 306(6): 364-365 ] , this has resulted in a RBE approaching 1,000 instead of the value used in governmental regulations.

The largest natural contributor to public radiation dose is radon, a naturally occurring, radioactive gas found in soil and rock [ [ ANS : Public Information : Resources : Radiation Dose Chart ] ] . If the gas is inhaled, some of the radon particles may attach to the inner lining of the lung. These particles continue to decay, emitting alpha particles which can damage cells in the lung tissue. [EPA Radiation Information: Radon. October 6 2006, [] , Accessed Dec. 6 2006] . The death of Marie Curie at age 66 from leukemia was likely caused by prolonged exposure to high doses of ionizing radiation. Curie worked extensively with Radium, which decays into Radon [Health Physics Society, "Did Marie Curie die of a radiation overexposure?" [] ] , along with other radioactive materials that emit beta and gamma rays.

The 2006 assassination of Russian dissident Alexander Litvinenko is thought to have been caused by poisoning with Polonium-210, an alpha emitter.

See also

*Beta decay


[ Alpha emitters by increasing energy (Appendix 1)]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • alpha decay — noun radioactive decay of an atomic nucleus that is accompanied by the emission of an alpha particle • Hypernyms: ↑decay, ↑radioactive decay, ↑disintegration * * * noun : the radioactive decay of an atomic nucleus by emission of an alpha particle …   Useful english dictionary

  • alpha decay — Physics. a radioactive process in which an alpha particle is emitted from the nucleus of an atom, decreasing its atomic number by two. [1935 40] * * * Type of radioactive disintegration (see radioactivity) in which some unstable atomic nuclei… …   Universalium

  • alpha decay — alfa skilimas statusas T sritis Standartizacija ir metrologija apibrėžtis Radioaktyviojo atomo branduolio savaiminis virsmas kitu branduoliu išspinduliuojant alfa daleles. atitikmenys: angl. alpha decay; alpha desintegration; alpha particle… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • alpha decay — alfa skilimas statusas T sritis fizika atitikmenys: angl. alpha decay; alpha particle decay vok. Alphaumwandlung, f; Alphazerfall, m rus. альфа распад, m pranc. désintégration alpha, f …   Fizikos terminų žodynas

  • alpha decay — alfa skilimas statusas T sritis apsauga nuo naikinimo priemonių apibrėžtis Savaiminis branduolio virsmas, kurio metu branduolys spinduliuoja ↑ alfa dalelę. Alfa skilimo metu susidaro radioaktyvusis branduolys, kurio eilės numeris, pradinio… …   Apsaugos nuo naikinimo priemonių enciklopedinis žodynas

  • alpha decay — alfa skilimas statusas T sritis chemija apibrėžtis Radioaktyviojo atomo branduolio virsmas, kurio metu išspinduliuojama alfa dalelė. atitikmenys: angl. alpha decay; alpha desintegration; alpha particle desintegration rus. альфа распад …   Chemijos terminų aiškinamasis žodynas

  • alpha decay — noun Radioactive decay by emitting an alpha particle …   Wiktionary

  • alpha decay — a form of radioactive decay in which an alpha particle (two neutrons plus two protons) is emitted, decreasing both the size and the charge of the nucleus and yielding a daughter product that is a different element. It often occurs serially …   Medical dictionary

  • alpha decay — /ælfə dəˈkeɪ/ (say alfuh duh kay) noun radioactive disintegration in which alpha particles are emitted …   Australian English dictionary

  • alpha decay energy — alfa skilimo energija statusas T sritis fizika atitikmenys: angl. alpha decay energy; alpha disintegration energy vok. Alpha Umwandlungsenergie, f; Alpha Zerfallsenergie, f rus. энергия альфа распада, f pranc. énergie de désintégration alpha, f …   Fizikos terminų žodynas

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”