- (a) Quarks are elementary particles.
(i) State what is meant by an elementary particle. [1]
(ii) List the fundamental forces that act on quarks. [4]
(iii) The lambda baryon (Λ⁰) has quark content uds. It decays according to the reaction Λ⁰ → p + π⁻. The quark content of the pion is ūd. State and explain which fundamental interaction is responsible for this decay. [2]
(b) (i) By reference to the concept of binding energy, explain why the combined mass of the nucleons of a nucleus is greater than the mass of the nucleus. [2]
(ii) The following binding energies per nucleon are available:
Th: 7.645074 MeV Ra: 7.679917 MeV He: 7.073915 MeV
Determine the energy released in the decay ²²⁸₉₀Th → ²²⁴₈₈Ra + ⁴₂He. [2]
(iii) It is observed that, sometimes, the alpha decay of thorium is accompanied by gamma‑ray emission. Suggest an explanation for this observation. [1]