Abstract The field of low-energy nuclear physics has long lacked a unified nuclear structure theory derived from first principles with both simplicity and comprehensive explanatory power. Classical phenomenological models such as the liquid drop model and shell model rely on empirical parameter fitting, and fail to explain a series of long-standing puzzles: the stable upper limit of N/Z≈1.5, binding energy peaks in light nuclei, the existence of stable odd-odd nuclei, and the microscopic nature of radioactive decay. Lattice QCD, constrained by non-perturbative calculations, can only handle extremely light nuclides and provides no intuitive physical picture. This paper proposes a **ud quark Coulomb pairing nuclear structure model** (referred to as the ud nuclear bond model): at low energy scales, the microscopic nature of nuclear force is the Coulomb coordination interaction between cross-nucleon u quarks (+2/3 e) and d quarks (−1/3 e); nucleon stability is determined by the symmetry of internal quark arrangement and torsional torque; atomic nuclei use α clusters as the basic saturated unit, and realize stacking evolution through bidirectional rugby-shaped deformation bridging of neutrons and unilateral external attachment of protons. With only one global correction parameter with clear physical meaning, the model can quantitatively calculate the binding energy of nuclides from hydrogen to uranium, with errors of less than 5% for more than 90% of key nuclides, and less than 2% for iron-group and heavy nuclei. Meanwhile, it derives the upper limit of N/Z≈1.5 for stable nuclides from first principles, and uniformly explains classic problems such as the full shape of the specific binding energy curve, the existence of stable odd-odd nuclei, the microscopic mechanism of α/β decay, the neutron skin of heavy nuclei, and the dual energy states of deuterons. The model can also be naturally extended to the microscopic layered structure of neutron stars. ### Version Information This is the **final complete version (v6.0)** of this theoretical work, which is a systematically improved, logically closed and quantitatively standardized final version based on previous phased research results. ### Previous Versions quark Coulomb pairing; nature of nuclear force; alpha cluster model; nuclide stability; neutron skin; neutron star structure; low-energy nuclear physics; nuclear binding energy
Wuyuan Zhuang (Fri,) studied this question.