Beta decay and quark flavour change

Overview

Recall questions on Beta decay and quark flavour change.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What happens to an individual quark during β⁻ decay?

   Model answer

   A down quark changes into an up quark, so the flavour of that quark is altered.

2. 2

   Write the equation for β⁻ decay at the level of the nucleons.

   Model answer

   n → p + e⁻ + ν̄ₑ. A neutron becomes a proton with the emission of an electron and an electron antineutrino.

3. 3

   Write the equation for β⁻ decay at the level of the quarks.

   Model answer

   d → u + e⁻ + ν̄ₑ. The neutron udd therefore becomes the proton uud.

4. 4

   Which of the four interactions is responsible for beta decay?

   Model answer

   Beta decay is brought about by the weak interaction.

5. 5

   Explain why the strong or electromagnetic interaction cannot cause beta decay.

   Model answer

   Neither the strong nor the electromagnetic interaction can change the flavour of a quark. Only the weak interaction can turn a down quark into an up quark or the reverse.

6. 6

   Why is a neutrino or antineutrino always involved in a beta decay?

   Model answer

   Lepton number must be conserved, and the electron created in β⁻ decay has lepton number +1. An antineutrino of lepton number −1 must accompany it so that the total stays at zero.

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