3.2.1.6
Beta decay involves a quark changing flavour
Quarks, Leptons & Conservation Laws — AQA A-Level Physics
- Beta decay occurs because the weak interaction can change one flavour of quark into another.
β⁻ decay at quark level
- A down quark changes into an up quark: $d \rightarrow u + e^{-} + \bar{\nu}_e$
- This converts a neutron ($udd$) into a proton ($uud$).
- The $W^{-}$ boson carries away the change in chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. It then decays into the electron and anti-neutrino.
β⁺ decay at quark level
- An up quark changes into a down quark: $u \rightarrow d + e^{+} + \nu_e$
- This converts a proton ($uud$) into a neutron ($udd$).
- The $W^{+}$ boson carries away the change in chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).. It then decays into the positron and neutrino.
Examiner Tips and Tricks
- In Feynman diagrams at quark level, you draw the individual quark changing flavour.
- The other two quarks in the nucleon are unaffected — they are sometimes called 'spectator quarks'.
Related:Particle Interactions