OCR A Level Physics

Revision Notes

6.8.4 Beta Minus & Beta Plus Decay

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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

Beta minus decay diagram, downloadable AS & A Level Physics revision notes

  • 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

 Beta minus decay equation, downloadable AS & A Level Physics revision notes

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

Beta plus decay diagram, downloadable AS & A Level Physics revision notes

  • 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

Beta plus decay equation, downloadable AS & A Level Physics revision notes

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 quarks, downloadable AS & A Level Physics revision notes

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 quarks, downloadable AS & A Level Physics revision notes

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

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