Beta Minus & Beta Plus Decay (OCR A Level Physics): Revision Note

Beta Minus and Beta Plus Decay

• Beta decay happens via the weak interaction

  • This is one of the four fundamental forces and it’s responsible for radioactive decays

Beta-Minus Decay

• A beta-minus, β^-, particle is a high energy electron emitted from the nucleus

• β^- decay is when a neutron turns into a proton emitting an electron and an anti-electron neutrino

• When a β^- particle is emitted from a nucleus:

  • The number of protons increases by 1: proton number increases by 1

  • The total number of nucleons stays the same: nucleon number remains the same

Equation for beta minus emission

• The new nucleus formed from the decay is called the “daughter” nucleus (nitrogen in the example above)

Beta-Plus Decay

• A beta-plus, β⁺, particle is a high energy positron emitted from the nucleus

• β⁺ decay is when a proton turns into a neutron emitting a positron (anti-electron) and an electron neutrino

• When a β⁺ particle is emitted from a nucleus:

  • The number of protons decreases by 1: proton number decreases by 1

  • The total number of nucleons stays the same: nucleon number remains the same

Equation for beta plus emission

Quark Model of Beta Minus Decay

• Recall that β^- decay is when a neutron turns into a proton emitting an electron and anti-electron neutrino

• More specifically, a neutron turns into a proton because a down quark turning into an up quark

Beta minus decay is when a down quark turns into an up quark

Quark Model of Beta Plus Decay

• Recall that β⁺ decay is when a proton turns into a neutron emitting an positron and an electron neutrino

• More specifically, a proton turns into a neutron because an up quark turns into a down quark

Beta plus decay is when an up quark turns into a down quark