An energetically allowed β⁺ decay occurs in a hypothetical nucleus with nucleon number 36 and proton number 15. Up and down quarks have charges +2e/3 and −e/3. (a) State the daughter's nucleon and proton numbers. (b) Describe the nucleon and quark changes and name both emitted leptons. (c) Check charge conservation at quark level.

Question

Accepted Answer

Daughter A = 36, Z = 14; p → n + positron + electron neutrino; u → d. Beta decay changes one nucleon type without removing a nucleon. Therefore A remains 36, while a proton becomes a neutron and Z falls to 14. A proton has quark composition uud and the resulting neutron is udd, so one up quark changes into a down quark. The other two quarks remain unchanged. The emitted leptons are a positron and an electron neutrino. At quark level, +2e/3 = −e/3 + e + 0, demonstrating that total electric charge is conserved. The charged beta particle is created in the decay; it is not an electron expelled from an atomic shell. The accompanying neutrino or antineutrino is electrically neutral and also carries energy and momentum. Energetic allowance is specified rather than inferred from charge bookkeeping alone.

Quark bookkeeping in beta-plus decay 4

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