1. Step 1: ${}_{Z}^{A}\mathrm{X} \rightarrow {}_{Z-2}^{A-4}\mathrm{D}_1$. Mass number decreases by 4 ($A \to A-4$) and atomic number decreases by 2 ($Z \to Z-2$). This corresponds to the emission of an \alpha particle ($\alpha$, ${}_{2}^{4}\mathrm{He}$) .
2. Step 2: ${}_{Z-2}^{A-4}\mathrm{D}_1 \rightarrow {}_{Z-1}^{A-4}\mathrm{D}_2$. Mass number remains unchanged ($A-4 \to A-4$), but atomic number increases by 1 ($(Z-2) \to (Z-1)$). This corresponds to the emission of a beta-minus particle ($e^-$, ${}_{-1}^{0}e$) .
3. Step 3: ${}_{Z-1}^{A-4}\mathrm{D}_2 \rightarrow {}_{Z-3}^{A-8}\mathrm{D}_3$. Mass number decreases by 4 ($(A-4) \to (A-8)$) and atomic number decreases by 2 ($(Z-1) \to (Z-3)$). This corresponds to the emission of another \alpha particle ($\alpha$, ${}_{2}^{4}\mathrm{He}$).
4. Step 4: ${}_{Z-3}^{A-8}\mathrm{D}_3 \rightarrow {}_{Z-4}^{A-8}\mathrm{D}_4$. Mass number remains unchanged, but atomic number decreases by 1 ($(Z-3) \to (Z-4)$). This corresponds to the emission of a positron ($e^+$, ${}_{+1}^{0}e$ or $\beta^+$) .
5. Step 5: ${}_{Z-4}^{A-8}\mathrm{D}_4 \rightarrow {}_{Z-4}^{A-8}\mathrm{D}_5$. Both mass number and atomic number remain unchanged. This indicates a transition from an excited state to a lower energy state via the emission of a \gamma ray ($\gamma$) .

Sequence: $\alpha, e^-, \alpha, e^+, \gamma$.