In physics, the decay mode describes a particular way a particle decays.

For radioactive decay (the decay of nuclides) the decay modes are:

• alpha decay (emission of a Helium-4 nucleus).
• β⁻ decay (emission of an electron)
• β⁺ decay (emission of a positron)
• electron capture
• proton emission
• spontaneous fission

Typically one decay mode predominates for a particular nuclide. Branching ratios are used when this is not true.

A decay will sometimes leave the nucleus in an excited state. When long lived these states are called isomers. These isomers will typically decay to the ground state of the nuclide, but unlike the radioactive decays above these isomeric transitions do not change one nuclide into others. These decays are:

• Emission of a high-energy photon (gamma emission)
• Ionizing the atom (internal conversion)