Interest in the continuous β-ray spectrum has been revived during the past few years by the discovery of induced β-ray activity and the difficulty which has been experienced in incorporating an account of the phenomenon in the theory of the nucleus. Attention has been focused on two features of the spectrum: the high-energy limit, the accurate measurement of which yields the total change in nuclear energy associated with the β disintegration, and the form of the energy distribution curve, which is discriminative in theories of the β-ray emission process. Owing to the convenience of R aE as a source, the β-ray spectrum of this element has received considerable attention, and a comprehensive table of previous work published in a recent paper by O’Conor (1937) shows that recent values of the high-energy limit obtained with magnetic spectrometers are in fair agreement. The form of the R aE spectrum, however, is still not known with any certainty. This can be made clear with the help of Table I, which sets out the results and significant experimental details of the work carried out since 1935 with magnetic spectrometers. Some recent work with cloud expansion chambers is not included because the results are rather discordant. With the relatively low energy electrons of R aE and the high probability of nuclear collisions in the chamber, measurements of the energies of the β-particles are extremely difficult, and the results are probably not as reliable as those obtained with magnetic spectrometers.
Climbing three-Reggeon ladders: Four-loop amplitudes in the high-energy limit in full color
