This paper proposes a novel neutron composite model, describing the neutron as a two-level bound state composed of a proton (p), an electron (eu207b), and a sterile antineutrino ��̄ ��) through electromagnetic and magnetic moment interactions. The core mechanism lies in the orbital instability caused by magnetic moment perturbations within the Wu207b bound state (eu207b-��̄ ��), which drives βu207b decay. By introducing quantization conditions for orbital angular momentum, a closed self-consistent system of equations is constructed and solved. For the first time, this theory directly derives key internal parameters of the neutron from first principles, including its radius (~1.28 fm) and the orbital velocity of the Wu207b bound state (~0.115c). It also predicts the magnetic moment of the sterile antineutrino (3.64×10u207b¹u2070����) and its relativistic velocity within the bound state (0.54c)[1]. Based on this framework, the neutron lifetime is naturally predicted as 878.4 seconds, with a deviation of only -0.20% compared to the experimental value (880.2±1.0 seconds)[2]. Furthermore, the probabilistic nature of decay (half-life) is attributed to quantum tunneling effects at the critical point of orbital instability, unifying the dynamical process of decay with quantum statistical outcomes within a single theoretical framework.