With only two electrons in the final state, the electrons' total kinetic energy would be approximately the binding energy difference of the initial and final nuclei, with the nuclear recoil accounting for the rest. Because of momentum conservation, electrons are generally emitted back-to-back. The decay rate for this process is given by Γ Γ = G | M | 2 | m β β β β | 2 , where G is the two-body phase-space factor, M is the nuclear matrix element, and m ββ is the effective Majorana mass of the electron neutrino. In the context of light Majorana neutrino exchange, m ββ is given by