The Beta-Ray Spectra ofCu64at Low Energies

An electrostatic beta-ray spectrometer has been constructed utilizing the focusing action of the electric field between concentric cylindrical conductors. A Geiger tube counter using an argon-alcohol mixture was used; a technique for making windows for the counter was developed whereby electrons of energies as low as 5 kev could be counted. A source of radioactive ${\mathrm{Cu}}^{64}$ was mounted on a very thin collodion film in order to eliminate the effects of back scattering. The positron and electron spectrum of ${\mathrm{Cu}}^{64}$ was plotted with the apparatus in the region below 50 kev. It was found that the ratio of the number of positrons to the number of electrons in this region did not agree with the number predicted by the Fermi theory of beta-disintegration.