The Coulomb barrier, named after Coulomb's law, which is named after physicist Charles-Augustin de Coulomb (1736–1806), is the energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a  nuclear reaction. This energy barrier is given by the electrostatic potential energy:

where

k is the Coulomb's constant = 8.9876×10⁹ N m² C^-2;

e₀ is the permittivity of free space;

q₁, q₂ are the charges of the interacting particles;

r is the interaction radius.