Electron capture

Nuclear physics

Radioactive decay Nuclear fission Nuclear fusion Classical decays Alpha decay · Beta decay · Gamma radiation · Cluster decay Advanced decays Double beta decay · Double electron capture · Internal conversion · Isomeric transition Emission processes Neutron emission · Positron emission · Proton emission Capturing Electron capture · Neutron capture R · S · P · Rp Fission Spontaneous fission · Spallation · Cosmic ray spallation · Photodisintegration Nucleosynthesis Stellar Nucleosynthesis Big Bang nucleosynthesis Supernova nucleosynthesis Scientists Henri Becquerel · Marie Curie · Pierre Curie

Electron capture (sometimes called Inverse Beta Decay) is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom and insufficient energy to emit a positron; however, it continues to be an inviable decay mode for radioactive isotopes that can decay by positron emission. If the energy difference between the parent atom and the daughter atom is less than 1.022 MeV, positron emission is forbidden and electron capture is the sole decay mode. For example, Rubidium-83 will decay to Krypton-83 solely by electron capture (the energy difference is about 0.9 MeV).

In this case, one of the orbital electrons, usually from the K or L electron shell (K-electron capture, also K-capture, or L-electron capture, L-capture), is captured by a proton in the nucleus, forming a neutron and a neutrino. Since the proton is changed to a neutron, the number of neutrons increases by 1, the number of protons decreases by 1, and the atomic mass number remains unchanged. By changing the number of protons, electron capture transforms the nuclide into a new element. The atom moves into an excited state with the inner shell missing an electron. When transiting to the ground state, the atom will emit an X-ray photon (a type of electromagnetic radiation) and/or Auger electrons.

$\mathrm {p} ^{+}+\mathrm {e} ^{-}\rightarrow \mathrm {n} +{\nu }_{e}\,$

examples:

$\mathrm {{}_{13}^{26}Al} +\mathrm {e} ^{-}\rightarrow \mathrm {{}_{12}^{26}Mg} +{\nu }_{e}$

$\mathrm {{}_{28}^{59}Ni} +\mathrm {e} ^{-}\rightarrow \mathrm {{}_{27}^{59}Co} +{\nu }_{e}$

$\mathrm {{}_{19}^{40}K} +\mathrm {e} ^{-}\rightarrow \mathrm {{}_{18}^{40}Ar} +{\nu }_{e}$

Radioactive isotopes which decay by pure electron capture can, in theory, be inhibited from radioactive decay if they are fully ionized ("stripped" is sometimes used to describe such ions). It is hypothesized that such elements, if formed by the r-process in exploding supernovae, are ejected fully ionized and so do not undergo radioactive decay as long as they do not encounter electrons in outer space. Anomalies in elemental distributions are thought to be partly a result of this effect on electron capture.

Chemical bonds can also affect the rate of electron capture to a small degree (generally less than 1%) depending on the proximity of electrons to the nucleus.[1]

Around the elements in the middle of the periodic table, isotopes that are lighter than stable isotopes of the same element tend to decay through electron capture, while isotopes heavier than the stable ones decay with a process called negative beta decay. A good example of this effect would be silver, as its light isotopes use electron capture and the heavier ones decay by negative beta emission.

See also

• Alpha decay
• Beta decay
• Radioactive decay

References

ISBN links support NWE through referral fees

• Krane, Kenneth S., and David Halliday. 1988. Introductory Nuclear Physics. New York: Wiley. ISBN 047180553X.

• Martin, Brian. 2006. Nuclear and Particle Physics: An Introduction. Hoboken, NJ: Wiley. ISBN 0470025328.

• Poenaru, D. N. 1996. Nuclear Decay Modes. Fundamental and Applied Nuclear Physics Series. Philadelphia: Institute of Physics. ISBN 0750303387.

• Seiden, Abraham. 2004. Particle Physics: A Comprehensive Introduction. San Francisco, CA: Addison Wesley. ISBN 0805387366.

• Tipler, Paul and Ralph Llewellyn. 2002. Modern Physics. 4th ed. New York, NY: W.H. Freeman. ISBN 0-7167-4345-0.

• Turner, James E. 1995. Atoms, Radiation, and Radiation Protection. 2nd ed. New York: Wiley. ISBN 0471595810.

External links

• Electron Capture. Jefferson Lab. Retrieved October 22, 2007.

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