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:

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:

(beta minus)

(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