The beta-ray spectrum of radium E was examined with a magnetic spectrometer, by using coincidence counting, under various conditions of source strength, mounting and aperture of defining slits. It is concluded that the experimental high energy end point depends on the source strength used, as well as the width of the defining slits. Data from all but very strong sources gave a K.U. plot which was linear within the limits of error set by statistical fluctuations and finite slit widths. Extrapolation of the K.U. plot gave 1.25±0.03 Mev as the high energy end point.

• Received 15 May 1937

DOI:https://doi.org/10.1103/PhysRev.52.303