Nucleus $P$ contains 144 neutrons and 93 protons. Nucleus $P$ is unstable and changes by $\alpha$-decay to produce nucleus $Q$. Nucleus $Q$ then changes by $\beta^-$ decay to produce nucleus $R$. On the graph, nucleus $P$ is shown by point $P$. Which point on the graph shows nucleus $R$?
Physics 9702 · AS & A Level · Atoms, nuclei and radiation