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Thomson is based on the assumption that the scattering due to a single atomic encounter is small, and the particular structure assumed for the atom does not admit of a very large deflexion of an α particle in traversing a single atom, unless it be supposed that the diameter of the sphere of positive electricity is minute compared with the diameter of the sphere of influence of the atom. His results apparently confirmed the main conclusions of the theory, and he deduced, on the assumption that the positive electricity was continuous, that the number of electrons in an atom was about three times its atomic weight. It was shown that the number N of the electrons within the atom could be deduced from observations of the scattering was examined experimentally by Crowther* in a later paper. θ, where θ is the average deflexion due to a single atom.The deflexion of the particle in passing through the atom is supposed to be small, while the average deflexion after a large number m of encounters was taken as m The deflexion of a negatively electrified particle in passing through the atom is ascribed to two causes - (1) the repulsion of the corpuscles distributed through the atom, and (2) the attraction of the positive electricity in the atom. The atom is supposed to consist of a number N of negatively charged corpuscles, accompanied by an equal quantity of positive electricity uniformly distributed throughout a sphere. 5 (1910)Įxplain the scattering of electrified particles in passing through small thicknesses of matter. A brief account of this paper was communicated to the Manchester Literary and Philosophical Society in February, 1911. A simple calculation shows that the atom must be a seat of an intense electric field in order to produce such a large deflexion at a single encounter.
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It seems reasonable to suppose that the deflexion through a large angle is due to a single atomic encounter, for the chance of a second encounter of a kind to produce a large deflexion must in most cases be exceedingly small. In addition, it will be seen later that the distribution of the α particles for various angles of large deflexion does not follow the probability law to be expected if such large deflexion are made up of a large number of small deviations. Geiger*** showed later that the most probable angle of deflexion for a pencil of α particles being deflected through 90 degrees is vanishingly small. thick, which was equivalent in stopping-power of the α particle to 1.6 millimetres of air. The observations, however, of Geiger and Marsden** on the scattering of α rays indicate that some of the α particles, about 1 in 20,000 were turned through an average angle of 90 degrees in passing though a layer of gold-foil about 0.00004 cm. It has generally been supposed that the scattering of a pencil of α or β rays in passing through a thin plate of matter is the result of a multitude of small scatterings by the atoms of matter traversed. There seems to be no doubt that such swiftly moving particles pass through the atoms in their path, and that the deflexions observed are due to the strong electric field traversed within the atomic system. This scattering is far more marked for the β than for the α particle on account of the much smaller momentum and energy of the former particle. It is well known that the α and the β particles suffer deflexions from their rectilinear paths by encounters with atoms of matter. Rutherford's Nucleus Paper of 1911 The Scattering of α and β Particles by Matter and the Structure of the AtomĪ scan of each page of this article from a copy of the journal itself may be found here.