Absolute Energies ofKα-Radiation from Thick Targets of Silver

Abstract

$K\alpha$-radiation from a thick silver target bombarded at 40 kev was isolated by Ross filters of 42 Mo and 45 Rh and the total energy measured with a large air-filled ion chamber and found to be 8.6 × ${10}^{-12\mathrm{}}$ erg per electron. This standardizes the curve of intensity vs. bombardment voltage measured in arbitrary units up to 180 kv by Webster, Hansen, and Duveneck. A quantitative explanation of the curve is developed upon the basis of the absolute cross section of the silver atom for $K$-ionization by electron impact, known over a considerable range of bombardment voltages from measurements by Webster, Hansen, and Duveneck and by J. C. Clark. From this cross section and the rate of energy loss of the bombardment electron the absolute energy of Ag $K\alpha$ is calculated and found to agree with the observed values within the limits of the errors of observation. The mass scattering coefficient of air at $\lambda 0.56\mathrm{A}$ is found by calculation to be 0.244 ${\mathrm{cm}}^2$ ${\mathrm{g}}^{-1\mathrm{}}$.