Alpha decay is an emission of a ₂⁴He nucleus. After an alpha decay, the formed daughter nuclide
has the reduced mass number by 4 and reduced atomic number by 2 with
compared to the parent atom.
After an alpha decay of ₉₂²³⁸U, the formed daughter atom should be Th (Thorium) which has atomic number as 92 - 2 =
90. The equation is,
₉₂²³⁸U → ₉₀²²⁹Th + ₂⁴He
The sum of mass
number and sum of atomic number should be equal in both side.
