$\beta$-particle is emitted in radioactivity by

During a $\beta$-decay,the mass of the atomic nucleus

What happens when an $\alpha$-particle is emitted?

$A$ radioisotope will not emit

The substance used in cancer therapy is

An atom has a mass number of $232$ and an atomic number of $90$. How many $\alpha$-particles should it emit after the emission of two $\beta$-particles,so that the resulting atom has a mass number of $212$ and an atomic number of $82$?