The maximum energy of the β-Rays from uranium X and other bodies

It is now generally accepted that the disintegration electrons from radioactive nuclei have a continuous distribution with energy. The end-points of these distribution curves, representing the maximum kinetic energies carried by the β-rays, have been determined in a considerable number of cases and appear to be quite definite. The purpose of this paper is twofold. First, new experimental work on the β-rays from uranium X will be presented in sections 2, 3 and 4. This includes a determination of the end-point of its normal β-ray spectrum, which was found to be 2·32 million volts, and a search for β-rays having energies from 3 to 7 million volts. None were found, and an upper limit on their number was determined. Secondly, a critical survey of the data on the end-points of a number of [3-ray spectra with a list of preferred values will be given in section 5. It will then be shown, in section 6, that a relation between the maximum energy emitted in a spectrum of β-rays and its disintegration constant appears to exist. 2. Methods of Determining the End-points of Continuous Spectra. Three methods have been used to find the maximum energies in β-ray spectra. One direct method, carried out principally by Madgwick and Gurney, consists of analysing the β-rays with the usual semicircular focussing in a magnetic field, and determining, from the field strength and the radius of curvature of the path, the velocity of the fastest particles that can be detected by electrical methods.