angles of deflection. The alpha particles emitted from A was narrowed to a beam by a small circular hole at D. Geiger placed a metal foil in the path of the rays at D and E to observe how the zone of flashes changed. He could also vary the velocity of the alpha particles by placing extra sheets of mica or aluminium at A. From the measurements he took, Geiger came to the following conclusions: the most probable angle of deflection increases with the thickness of the material the most probable angle of deflection is proportional to the atomic mass of the substance the most probable angle of deflection decreases with the velocity of the alpha particles the probability that a particle will be deflected by more than 90° is vanishingly small Rutherford mathematically models the scattering pattern Considering the results of the above experiments, Rutherford published a landmark paper in 1911 titled "The Scattering of α and β Particles by Matter and the Structure of the Atom" wherein he proposed that the atom contains at its center a volume of electric charge that is very small and intense (in fact, Rutherford treats it as a point charge in his calculations). For the purpose of his mathematical calculations he assumed this central charge was positive, but he admitted he could not prove this and that he had to wait for other experiments to develop his theory. Rutherford developed a mathematical equation that modeled how the foil should scatter the alpha particles if all the positive charge and most of the atomic mass was concentrated in a single point at the center of an atom. s = the number of alpha particles falling on unit area at an angle of deflection Φ r = distance from point of incidence of α rays on scattering material X = total number of particles falling on the scattering material n = number of atoms in a unit volume of the material t = thickness of the foil Qn = positive charge of the atomic nucleus Qα = positive charge of the alpha particles m = mass of an alpha particle v = velocity of the alpha particle From the scattering data, Rutherford estimated the central charge Qn to be about +100 units (see Rutherford model) The 1913 experiment In a 1913 paper, The Laws of Deflexion of α Particles through Large Angles, Geiger and