The Weak Interaction (AQA A Level Physics): Revision Note

The Weak Interaction

• The weak interaction is responsible for the radioactive decay of atoms

• The exchange particle that carries this force is the W^–, W⁺ or Z⁰ boson

  • The type of exchange particle depends on the type of interaction

β decay

• β^– and β⁺ decay are examples of the weak interaction in action

• In β^– decay, a neutron turns into a proton emitting an electron and an anti-electron neutrino

• The W^– boson is the exchange particle in this interaction

Feynman diagram showing beta minus decay. The W^– boson is the exchange particle

• In β⁺ decay, a proton turns into a neutron emitting a positron and an electron neutrino

• The W⁺ boson is the exchange particle in this interaction

Feynman diagram showing beta plus decay. The W⁺ boson is the exchange particle

Electron Capture & Electron–Proton Collisions

• Electrons and protons are attracted to each other via the electromagnetic interaction

  • However, when they interact with each other, it is the weak interaction that facilitates the collision

• Both electron capture and electron-proton collisions have the same decay equation

• Electron capture is when an atomic electron is absorbed by a proton in the nucleus resulting in the release of a neutron and an electron neutrino

  • This decay is mediated by the W⁺ boson

• Electron-proton collisions are similar; when an electron collides with a proton, a neutron and an electron neutrino are emitted

  • This decay is mediated by the W^– boson

Feynman diagrams for electron capture and an electron-proton collision. These are equal except for the sign of the W boson