Explore experiments

The gold foil: finding the nucleus

One grid cell is 10 femtometres. One mass unit is one atomic mass unit, one charge unit is one elementary charge — so the nucleus on screen literally reads mass 197, charge 79, and that is gold. Eleven alpha particles enter at 1.5 x 10^7 m/s, each aimed to miss by a different distance. Nothing here is a scattering formula being drawn: it is Coulomb's law with the real constant, integrated 120 times a second, and the one aimed dead centre stops 29.6 fm out and comes back.