Nickel sheets approximately 5×${10}^{-6\mathrm{}}$ cm in thickness were bombarded with 70 kv electrons and the intensity of the resulting $K\alpha$ radiation was measured by a special air-filled ionization chamber connected to a calibrated quadrant electrometer. Isolation of the $K\alpha$ line was effected by Ross filters of cobalt and iron, supplemented by additional filters for evaluation of a correction for the continuous background radiation. After due consideration of the effects of electron scattering in the target and all relevant x-ray absorptions, it was concluded from the observed intensities that the cross section of the nickel atom for $K$ ionization by 70 kv electrons is (3.38±0.2) × ${10}^{-22\mathrm{}}$ ${\mathrm{cm}}^2$. From this result and Williams' equation for electron energy loss it is deduced that the efficiency of production of nickel $K$-radiation by electrons of 70 kev energy is 0.35 percent.

• Received 10 December 1944

DOI:https://doi.org/10.1103/PhysRev.67.153