The diagram presents a section of a radioactive decay series in which the nuclide thorium-$232$ undergoes $\alpha$-emission to form radium-$228$. This nuclide is also unstable and undergoes $\beta$-emission to produce a nuclide of actinium. The sequence then proceeds further. $^{{232}}_{{90}}\text{Th} \xrightarrow{\alpha} ^{{228}}_{{88}}\text{Ra} \xrightarrow{\beta} ^{{X}}_{{89}}\text{Ac} \xrightarrow{Y} ^{{228}}_{{90}}\text{Th} \xrightarrow{\alpha} ^{{224}}\text{Z} \rightarrow$ What are $X$, $Y$ and $Z$?
Physics 9702 · AS & A Level · Atoms, nuclei and radiation