Question

The empirical mass formula is 

^A_ZM = 0.99198A − 0.000841Z + 0.01968A^2/3 + 0.0007668Z² A^−1/3 +0.09966(Z − A/2)²A⁻¹ − δ

in atomic mass units, where δ = ±0.01204 A^−1/2 or 0. 

Determine whether or not the nuclide ²⁷₁₂Mg is stable to β decay.

Answer 1

As the right hand side is positive ²⁷₁₂Mg is heavier than ²⁷₁₃Al, and therefore it is unstable against β− decay.