The nucleus was postulated as small and dense to account for the scattering of alphaparticles from thin gold foil, as observed in a series of experiments performed under Rutherford’s direction in 1910–11 (see Figure). The diagram shows a simplified plan of his gold foil experiment. Aradioactive source capable of emitting alpha particles (i.e., positively charged particles more than 7,000 times as massive as electrons) was enclosed within a protective lead shield.
[The RutherfordModel of the Nuclear Atom]
Considering the results of Geiger and Marsden's experiment and the failure of Thomson's atomic model, E. Rutherford (UK, 1871 - 1937) proposed a model in which theelectric charge +Ze in an atom is not distributed over the whole area of the atom but concentrates in a small area (1911).
He thought as follows: The charge +Ze is localized to be acluster or a group and the alpha particle is scattered by Coulomb's repulsive force, (C. A. de Coulomb: France, 1736 - 1806). Namely, his idea is that the large-angle scattering of the alphaparticle is brought about by a single scattering due to Coulomb's repulsive force between the charge of the alpha particle, +2e, and that of the cluster, +Ze. The cluster is called atomicnucleus or simply nucleus. Rutherford's atomic model is often called Rutherford model or sometimes Rutherford model of the nuclear atom.
A schematic image of the Rutherford model is shown in...