alpha decay is an emission of ₂⁴He
nucleus. If an element undergoes an alpha decay, the mass of the daughter
nucleus formed is reduced by 4 compared to mass of parent atom and atomic
number is reduced by 2 compared to atomic number of parent atom.
Let's assume that the parent atom is X, atomic number is z and mass number is A. Then the formed daughter nucleus, Y should have atomic number as z-2 and mass number as A-4.
The equation is
(z) (A)X → ₂⁴α + (z-2)(A-4)Y
Example:
₉₄²³⁹Pu → ₂⁴α + ₉₂²³⁵U
