Mass absorption coefficients for wave-lengths on both sides of the K limit.

(1)Experimental results for six metals. Using a water cooled Mo tube, absorption measurements were made for a sufficient range of wave-lengths in each case to determine the constants in the equations for the mass absorption coefficients above and below the K absorption discontinuity. $\frac{{\mu }_{\mathrm{K}}}{\rho }={\mathrm{K}}_{\mathrm{K}}{\lambda }^3+\frac{\sigma }{\rho }$; $\frac{{\mu }_{\mathrm{L}}}{\rho }={\mathrm{K}}_{\mathrm{K}}{\lambda }^3+\frac{\sigma }{\rho }$, in which $\frac{\sigma }{\rho }$ is the scattering coefficient, with a value of 1 or less. $\lambda$ is in angstrom units. ${\tau }_a$ is the atomic absorption coefficient at the K limit, corrected for scattering.

(2)Comparison with theories. ($\frac{k_{\mathrm{K}}}{k_{\mathrm{L}}}-1\mathrm{}$) is the ratio of the number of photo-electrons originating in the K and L levels for x-rays just shorter than the K limit. It is shown that the theories of Thomson, of Compton, and of de Broglie lead to the same values of $\frac{k_{\mathrm{K}}}{k_{\mathrm{L}}}$, which increase with decreasing atomic number in agreement with experiment except that they are about twice too large. Kramers' formula gives a value which does not vary with N and which agrees well with the experimental values for Mo to Pb, but it applies only to a single electron around the nucleus. A formula modified by use of Bohr's theory of energy levels to remove this restriction gives values nearly three times too large. No present theory, then, is supported by these experimental results.

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