A Measurement of the Absolute Probability ofK-Electron Ionization of Silver by Cathode Rays

The method of Ross's balanced foils was used to separate the $K\alpha$ quanta from the thin silver foil target radiation. The x-ray energy was absorbed in C${\mathrm{H}}_3$Br and S${\mathrm{O}}_2$ in a standard ionization chamber and the ionization currents measured by means of a Compton electrometer and calibrated ionization system. Stockmeyer's value for the energy per ion pair for these gases was used to compute the number of quanta absorbed in the chamber. The number of Ag $K$ ionizations per bombarding electron was then calculated, after the necessary target and absorption corrections. Measurements were made on 10 thin targets of average thickness 0.17 micron, and the $K$-electron ionization cross section for silver for 70.0 kv electrons was determined to be $\Phi \mathrm{}\left(U\right)=(4.80\mathrm{}\pm 0.43)\times {10}^{-23\mathrm{}}$ ${\mathrm{cm}}^2$. The measurements of relative probabilities of $K$ electron ionization for silver by Webster, Hansen and Duveneck are normalized at 70.0 kv, ($U=2.75\mathrm{}$) by the above value of $\Phi \mathrm{}\left(U\right)\mathrm{}$, and these experimental data compared with classical quantum theory and the wave mechanics theories of Massey, Mohr and Burhop, Soden and Wetzel. The theories of Soden and Wetzel compare more favorably with the experimental data than those of Massey, Mohr and Burhop, or indeed with the classical theory.