ELECTRON-SLOWING-DOWN SPECTRUM IN Cu OF BETA RAYS FROM Cu$sup 6$$sup 4$

The electron flux spectrum resulting from the slowing down of electrons from /sup 64/Cu uniformly distributed in Cu was measured from 0.1 ev to 37 kev for both a plane disk source and a black body cavity source. The cavity source consisted of a hollow Cu frustrum with walls infinitely thick for /sup 64/Cu beta rays. A matching thick cover allowed only electrons from inside the cavity to enter the Keplertron, a spherical electrostatic beta spectrometer. The cavity data agreed well from 1 kev to 37 kev with a simplified calculation of the Spencer-Fano theory. Below 1 kev, the experimental flux exceeded the calculated flux by as much as 35% at 30 ev. A stopping power derived from proton dath was used in the theory for electrons below 5.5 kev. A buildup of several orders of magnitude in the electron flux below 1 kev was observed. The disk data was lower than the cavity data at all energies above 1 kev, the former approaching the latter at higher energies. The beth spectrometer was calibrated for transmission and resolution from 1.5 ev to 3 kev using an isotropic electron gun and at 31.4 kev using the /sup 152/Sm Auger line. (auth