On the capture of electrons by moving electrified particles

When an α-particle passes through matter it may capture an electron and continue on its way as a singly ionised helium atom. It is of interest to calculate the chance of such a capture on a classical basis and compare the results with the experimental data of Rutherford, Henderson, and Jacobsen. Fowler has calculated this chance by applying equilibrium statistical theory although the conditions do not very closely resemble equilibrium conditions. In the following paper the process of capture is considered in detail, and two cases are treated in which the three-body collision which is involved can be broken up into two successive two-body collisions. I.—On the Capture of Electrons from Light Atoms by very Swift Particles. Supposea particle of charge E moves with velocity V through matter containing atoms per unit volume, each atom consisting of a nucleus of charge Z surrounded by electrons of chargee and massm at distancesr , and that is large compared with the velocities of the electrons. The sequence of event in a capture must be like that indicated in diagram 1; corresponding number on the two paths represent simultaneous positions of the particle and the electron. First there is a close “collision” of the particle and the electron at A, in which the electron has its small velocity altered nearly to V and so must go off at nearly 60° to the direction of motion of the particle; then the election must pass near the nucleus at B and be deflected through nearly 60 to the its direction of motion nearly parallel to that of the particle ; at the same time the particle will have reached C, where ABC is nearly enough an equilateral triangle.