(a)[1]
From the list below, underline every particle that is a lepton: antineutrino, positron, proton, quark.
(b)
A magnesium-27 nucleus at rest, $^{27}_{12}\text{Mg}$, decays by emitting a $\beta^-$ particle and $\gamma$ radiation. An incomplete equation to show this decay is $^{27}_{12}\text{Mg} \rightarrow X + \beta^- + \gamma$.
(b(i))[2]
State the nucleon number together with the proton number for nucleus $X$.
(b(ii))[1]
State the interaction responsible for this decay.
(b(iii))[2]
State two possible reasons why the combined kinetic energy of the $\beta^-$ particle and the energy of the $\gamma$ radiation is smaller than the total energy released when the magnesium nucleus decays.