= Liquid-drop fission energy
{title2=$Q(y)=a_SA^{2/3}[1-y^{2/3}-(1-y)^{2/3}]+a_CZ^2A^{-1/3}[1-y^{5/3}-(1-y)^{5/3}]$}
For two spherical fragments with the same proton fraction as the parent, let $(A_1,Z_1)=y(A,Z)$ and $(A_2,Z_2)=(1-y)(A,Z)$. In the <semi-empirical mass formula> without <nuclear pairing>, nucleon rest energies, the volume term and the <nuclear symmetry energy> cancel in the parent-minus-fragment mass difference. The remaining <Q value> is the displayed competition between increased surface energy and reduced <nuclear Coulomb energy>. Its symmetric value is positive when
$$
\frac{Z^2}{A}>\frac{a_S}{a_C}\frac{2^{1/3}-1}{1-2^{-2/3}}.
$$
This is an energy-release condition, not the disappearance of a <fission barrier> or a prediction of a short <mean lifetime>.
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