The magnetic spectrum of the β-rays excited by γ-rays

Abstract

In recent years, the photo-electric effect of light has been worked out in considerable detail, especially as regards the dependence of the velocity of the ejected electron on the frequency of the absorbed light, but very little knowledge exists about the analogous phenomenon in the region of higher frequencies. A very simple method of investigating the velocities of the β -rays was used by Rutherford, Robinson, and Rawlinson. They found that the γ-rays from radium B and C, when passed through heavy metals, such as gold or lead, caused the emission of several groups of electrons, each group consisting initially of electrons of the same velocity. They showed that this fact alone gave information about the connection between the β -rays and γ -rays of radio-active bodies, but, in addition, they made the interesting observation that the velocity of the electrons liberated from gold had 1 to 2 per cent, higher velocity than those from lead. This fact receives a simple explanation if it be assumed that the energy of the emitted electron is equal to some energy characteristic only of the γ -ray, minus the energy necessary to remove the electron from the atom. The difference in the energies of the electrons ejected from gold and lead by the same γ -rays is then explained by the difference in the work of removal of these electrons from their respective atoms. Since the general relation of the gold atom to the lead atom is known, it should be possible to deduce from the experimental values for this difference in the work of removal, from what part of the atom the electron originated, and then values might be obtained for the energy characteristic of the γ -ray. The work to be described was undertaken with these points in view, the experimental determination consisting in the measurement of the energies of the electrons ejected from various metals by the γ -rays of radium B and C, with the special object of measuring accurately the differencies of these energies from metal to metal. As wide a range of metals as was practicable was used, in order to test any explanation of these energy differences.