Beta decay - Definition and Overview

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⁻), while in the case of a positron emission as "beta plus" (β⁺).

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

<math>\mathrm{n}\rightarrow\mathrm{p}+\mathrm{e}^-+\bar{\nu}_e<math>

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

<math>\mathrm{p}\rightarrow\mathrm{n}+\mathrm{e}^++{\nu}_e<math>

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

<math>\mathrm{{}^1{}^{37}_{55}Cs}\rightarrow\mathrm{{}^1{}^{37}_{56}Ba}+\mathrm{e}^-+\bar{\nu}_e<math> (beta minus)

<math>\mathrm{~^{22}_{11}Na}\rightarrow\mathrm{~^{22}_{10}Ne}+\mathrm{e}^++{\nu}_e<math> (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

• beta particle
• positron emission
• particle radiation
• radioactive isotope