Beta decay

Nuclear processes

Neutron Capture
- The R-process
- The S-process
Proton capture:
- The P-process

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⁺).

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

$\mathrm{n}\rightarrow\mathrm{p}+\mathrm{e}^-+\bar{\nu}_e$

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

$\mathrm{p}\rightarrow\mathrm{n}+\mathrm{e}^++{\nu}_e$

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.

Beta decay

See also