Neptunium-237 has a Atomic mass of 237 g/mol. The reaction of decay is shown as, ²³⁷₉₃Np ---------> ᵇₐX + ⁴₂He
where, X = Unknown Element
ᵇ = Atomic Mass of Unknown Element
ᵃ = Atomic number of Unknown Element
Solving for ᵇ,
237 = ᵇ + 4
ᵇ = 237 - 4
ᵇ = 233
Solving for ₐ ,
93 = ₐ + 2
ₐ = 93 - 2
ₐ = 91
Now, Putting values in ᵇ and ₐ of X,
²³³₉₁X
Searching Periodic table for atomic number 91.
²³³₉₁Pa
Result: The child Isotope is Protactinium (Pa) having atomic number 91 and Atomic mass 233 g/mol