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Beta decay

(Redirected from Beta emission)
Nuclear processes

Radioactive decay processes


In nuclear physics, beta decay (sometimes called neutron decay) is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. In the case of electron emission, it is referred to as "beta minus" (β); in the case of a positron, "beta plus" (β+) (positron emission).

In β decay, the weak nuclear force converts a neutron into a proton while emitting an electron and an anti-neutrino:


In β+ decay, a proton is converted into a neutron, a positron and a neutrino:


If the proton and neutron are part of an atomic nucleus, these decay processes transmute one chemical element into another. For example:

\mathrm{{}^1{}^{37}_{55}Cs}\rightarrow\mathrm{{}^1{}^{37}_{56}Ba}+\mathrm{e}^-+\bar{\nu}_e (beta minus)
\mathrm{~^{22}_{11}Na}\rightarrow\mathrm{~^{22}_{10}Ne}+\mathrm{e}^++{\nu}_e (beta plus)

Historically, the study of beta decay provided the first physical evidence of the neutrino. The energies of electrons emitted by beta decay were observed to be non-discrete (some being more energetic than others). A problem arose in trying to explain what happened to the missing energy if an electron was emitted with less than maximum energy — the law of conservation of energy appeared to be violated. To solve this, Wolfgang Pauli proposed that the "missing" energy was actually carried away by another yet undiscovered particle — the neutrino. This was analysed in more detail by Enrico Fermi.

The Beta decay can be considered as a perturbation as described in quantum mechanics, and thus follow Fermi's Golden Rule.

See also

Last updated: 03-01-2005 22:12:50