IV.R138 — Neutron stability inside nuclei

Free neutrons decay in ~10 minutes, but neutrons inside most nuclei are stable because nuclear binding lowers the neutron's effective mass, making Q_beta = (m_n - m_p - m_e)c^2 - B_n + B_p negative; when Q_beta < 0 the decay is energetically forbidden --- a readout-level phenomenon, the ontic neutron being unchanged.