Further Experimental Tests of Theories of the Absorption of X-Rays

When a beam of x-rays passes through a slab of absorbing material photo-electrons are in general expelled from all levels. If the beam is (1) monochromatic and (2) of wave-length shorter than the $K$ absorption limit of the absorber, the ratio, ${R_L}^K$, of the number of photoelectrons coming from ($K, L, M\cdots$) levels to the number coming from ($L, M\cdots$) levels is given by the maximum value ${\tau }_{max}$ reached by the atomic absorption coefficient as the limit is approached from the short wave-length side to the minimum value ${\tau }_{min}$ reached as the limit is approached from the long wave-length side. Because of absence of data on scattering coefficients it is impossible to obtain accurate experimental values of ${R_L}^K$ for purposes of comparing with experiment the theories of x-ray absorption proposed by Thomson, Compton, de Broglie and Kramers. A careful repetition of the measurements previously reported (Phys. Rev. 27, 1 (1926) shows that, after making any reasonable assumption as to the magnitude of scattering coefficients, the experimental values of ${R_L}^K$ are more nearly in agreement with Kramer's theory, excepting for a small observed variation of ${R_L}^K$ with $\lambda$. However the absolute magnitude of the absorption discontinuity, i.e. ${\tau }_{max}-{\tau }_{min}$, is given very closely by de Broglie's theory.