Positive Ray Analysis of Lithium and Magnesium

Isotopes of lithium and magnesium have been determined by positive ray analysis, using the apparatus and method previously described in which the positive ray spectrum is determined by measuring the charge passing through a fixed slit into a Faraday cylinder as a function of the accelerating difference of potential keeping the deflecting magnetic field constant. The source of the rays was a small cylindrical anode containing the metal to be studied, which was heated by a concentric coil and bombarded by electrons. It was found that there are two isotopes of lithium with atomic weights 6 and 7, while magnesium has three isotopes with atomic weights 24, 25 and 26. The relative proportions of the isotopes of lithium varied with the conditions. For magnesium the relative numbers were 7: 1: 1. Compensation Method of Measuring Small Currents.-The current to be measured is balanced by the current through an ionization chamber, which is adjusted to equality by varying the width of the slit through which the ionizing beta rays pass.