Radioactive Decay

Radioactive decay is the spontaneous transformation of an unstable nucleus into a more stable configuration through the emission of particles or electromagnetic radiation.

Definition

Radioactive decay is the statistical, spontaneous process by which an unstable atomic nucleus loses energy by emitting alpha particles, beta particles, or gamma rays, transforming into a different nuclide at a rate characterized by its half-life.

Scope

This topic covers the three classic modes of radioactivity, alpha, beta, and gamma decay, together with related processes such as electron capture and internal conversion. It treats the exponential decay law and the concept of half-life, the quantum-tunneling explanation of alpha decay, the weak-interaction origin of beta decay, and decay chains that lead unstable nuclei toward the valley of stability.

Core questions

• What distinguishes alpha, beta, and gamma decay?
• Why does decay follow an exponential law with a fixed half-life?
• How does quantum tunneling explain the rates of alpha decay?
• How is beta decay tied to the weak interaction and the neutrino?

Key concepts

• Alpha decay
• Beta decay and electron capture
• Gamma emission and internal conversion
• Half-life and decay constant
• Quantum tunneling
• Decay chains

Key theories

Gamow theory of alpha decay

Gamow explained alpha decay as quantum tunneling of an alpha particle through the Coulomb barrier, accounting for the strong dependence of half-life on decay energy.

Fermi theory of beta decay

Fermi formulated beta decay as a weak-interaction process in which a neutron converts to a proton with emission of an electron and an antineutrino, predicting the shape of the beta energy spectrum.

Clinical relevance

Radioactive decay enables radiometric dating of rocks and artifacts, powers radioisotope thermoelectric generators, and provides the radioisotopes used in medical imaging and radiation therapy, while its products and radiation require careful handling for radiological safety.

History

Radioactivity was discovered by Becquerel in 1896 and investigated by Marie and Pierre Curie, while Rutherford distinguished alpha, beta, and gamma radiation and formulated the exponential decay law. Gamow's 1928 quantum-tunneling theory of alpha decay and Fermi's 1934 theory of beta decay placed radioactive decay on a firm quantum-mechanical footing, the latter introducing the weak interaction and confirming Pauli's neutrino hypothesis.

Key figures

• Ernest Rutherford
• George Gamow
• Enrico Fermi
• Marie Curie

Seminal works

• gamow1928
• fermi1934

Frequently asked questions

Can we predict when a single nucleus will decay?

No. Radioactive decay is fundamentally random for an individual nucleus. Only the probability of decay in a given time, and hence the statistical behavior of large numbers of nuclei, can be predicted through the half-life.

What is the difference between alpha and beta decay?

Alpha decay emits a helium nucleus, reducing the mass number by four, and is governed by the strong and electromagnetic forces. Beta decay converts a neutron and proton into one another via the weak interaction, emitting an electron or positron and a neutrino.