Atom Builder.

n (udd) → p (uud) + e⁻ + ν̄ₑ

A down quark becomes an up quark through the weak interaction, mediated by a virtual W⁻: d → u + W⁻*, W⁻* → e⁻ + ν̄ₑ. This is one quantum process; the W is not an on-shell particle flying out of the nucleus. The electron and electron antineutrino are created in the decay, not stored inside the neutron.

Z increases by 1, N decreases by 1, and A = Z + N stays fixed. Charge is conserved: 0 = (+1) + (−1) + 0. Lepton number is conserved: 0 = 1 − 1; baryon number stays 1. The beta electron escapes; it does not join the bound shells or automatically neutralize the atom.

Removing a proton with the controls takes it out of the nucleus; it does not turn it into a neutron. A proton-to-neutron change by beta-plus decay emits a positron and an electron neutrino: p → n + e⁺ + νₑ. That is a different channel and is not animated here.

Decay must be energetically allowed by the parent and daughter nuclear states. Removing a proton can create a beta emitter, but neutron–proton counts alone do not establish a decay channel. We demonstrate the first listed IAEA mode only when it is ordinary β⁻.

Decay Now advances the simulation by one decay. Your atom stays unchanged until you click or edit it. Real radioactive decay is spontaneous; the button is a teaching control. The 0.8-second animation is unrelated to the measured half-life shown in the isotope details. A half-life describes an ensemble, not a deadline for one nucleus.

Paths, speeds, and the visible conversion are schematic. Actual decays share energy and momentum between the electron, antineutrino, and recoiling daughter. We do not simulate spectra, angular correlations, recoil, competing branches, gamma cascades, isomers, or changes in decay rates caused by ionization. A daughter may still be radioactive; click Decay Now again for another supported β⁻ step.

Berkeley Lab: beta decay ↗ · DOE: quarks and the weak force ↗