The process allows a nuclear interaction to take place at lower energies than would be expected from a simple calculation of the Coulomb barrier between a deuteron and a target nucleus. This is because, as the deuteron approaches the positively charged target nucleus, it experiences a charge polarization where the "proton-end" faces away from the target and the "neutron-end" faces towards the target. The fusion proceeds when the binding energy of the neutron and the target nucleus exceeds the binding energy of the deuteron itself; the proton formerly in the deuteron is then repelled from the new, heavier, nucleus.