Question

How many '$\alpha$' and'$\beta$'-particles will be emitted when ${}_{90}{Th}^{234}$ changes into ${}_{84}{Po}^{218}$?

Answer 1

The change is;
$\begin{array}{c}{}_{90}{Th}^{234}\\ Parent\end{array}⟶\begin{array}{c}{}_{84}{PO}^{218}\\ Endproduct\end{array}$
Decrease in mass $=(234-218)=16amu$
Mass of $1$ $\alpha$-particle $=4amu$
Therefore, number of $\alpha$-particles emitted $=\frac{16}{4}=4$
Number of $\beta$-particles emitted $=2\times$ Number of $\alpha$-particles emitted $-$ (Atomic number of parent $-$ Atomic number of end product)
$=2\times 4-(90-84)=(8-6)=2$
Hence, number of $\alpha$-particles emitted $=4$
and number of $\beta$-particles emitted $=2$