What is inside an atom?
Send alpha particles into a thin target. Watch where they go, compare two atomic models, and use the evidence to build a conclusion.
Scattering angles detected particles
No particles detected yet.
What can we conclude?
Conclusions use random-beam results. Aimed examples are labelled separately.
How the model works · scale, assumptions & sources
Paths are calculated from repulsive electric forces, not selected randomly from preset angles. Both models receive the same incoming particles. The nuclear model has a concentrated positive charge with a simple spherical electron-screening field; the plum pudding model spreads that positive charge across the atom. Individual electron collisions, recoil, energy loss and quantum effects are omitted. The mass is normalised; the energy slider scales the repulsion-to-kinetic-energy ratio.
Atom spacing, nuclear markers and the interaction region are deliberately enlarged for visibility. This is a two-dimensional slice with exaggerated close-encounter frequency, so the percentages are illustrative and are not physical predictions for real gold foil. The nucleus marker is a symbol, not a solid obstacle; backscattering is electric repulsion before contact. The displayed 1–2 layers are an ideal teaching target, not the thickness of the historical foil.
The beam runs for the selected count or simulated beam-on time, then lets all particles reach the ideal detector boundary. “Fire one” and the near-nucleus example are aimed demonstrations; their counts and angles are excluded from the random-beam histogram and conclusions. Changing thickness or energy starts a fresh dataset. Playback speed affects viewing time only, not a computed trajectory.
Historical foundation: E. Rutherford (1911), The Scattering of α and β Particles by Matter and the Structure of the Atom. The conclusions about a small, concentrated scattering centre follow the scattering evidence; electron arrangements and the existence of neutrons cannot be established by this experiment alone.