In a radioactive decay chain, ${ }_{90}^{232} \mathrm{Th}$ nucleus decays to ${ }_{82}^{212} \mathrm{~Pb}$ nucleus. Let $N_\alpha$ and $N_\beta$ be the number of $\alpha$ and $\beta^{-}$particles, respectively, emitted in this decay process. Which of the following statements is (are) true?
