Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso

Alpha Rays

  • Jun-Ichi Takahashi
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_55-2



An alpha ray is a stream of alpha particles. An alpha particle consists of two protons and two neutrons bound together into a particle identical to a helium nucleus; it is produced in the radioactive process called alpha decay. Alpha particles, like helium nuclei, have a net spin of zero. The energy of alpha particles varies, depending upon the specific decay reaction, with higher-energy alpha particles being emitted from larger nuclei, but most alpha particles have energies of between 3 and 7 MeV, corresponding to extremely long to extremely short half-lives of alpha-emitting nuclides. They are a highly ionizing form of particle radiation that when resulting from radioactive alpha decay have low penetration depth. Helium nuclei, which form 10–12 % of cosmic rays, are usually of much higher energy than those produced by radioactive decay.

See Also


Penetration Depth Alpha Particle Radioactive Decay Large Nucleus Particle Radiation 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.NTT Microsystem Integration LaboratoriesAtsugiJapan