Structural Decomposition of the Neutron-Proton Mass Difference: Precise Closure of 1.293 MeV

The mass difference between the neutron and the proton plus electron is 1.293 MeV/c², a value treated in the Standard Model of particle physics as the experimentally measured Q-value of neutron β-decay, whose internal structure is not questioned by the theory. This paper demonstrates that 1.293 MeV can be precisely decomposed into the sum of the energies of two independent physical processes: the constraint release share of 0.511 MeV (i.e., the electron rest energy, independently derived from stable nuclide data in a preceding paper) and the kinetic release share of 0.782 MeV (the electron energy spectrum endpoint value of neutron decay, independently determined by direct experimental measurement). The sum of the two precisely closes: 1.293 = 0.511 + 0.782. This precise decomposition shows that the neutron-proton mass difference is not an irreducible fundamental quantity, but the sum of two channels of energy release in a disintegration event. Together with the independent derivations of electron rest energy and proton mass in the two preceding papers, three core entries in the table of fundamental constants—electron rest energy, proton mass, and neutron-proton mass difference—have all been shown to be not original settings of the universe, but the results of energy distribution through different channels in the same neutron disintegration event.