The True Absorption Coefficients for the Elements from Gold to Bismuth in the Neighborhood of theL-Absorption Edges

Abstract

The $L$ x-ray absorption spectra of the metals gold to bismuth were examined with a calcite crystal spectrometer and ionization chamber. Thin films of thallium, lead and bismuth were evaporated onto very thin sheets of mica. The true absorption coefficients $\tau \left(L_{\mathrm{I}}\right)$, $\tau \left(L_{\mathrm{II}}\right)$, and $\tau \left(L_{\mathrm{III}}\right)$ corresponding to the photoelectric absorption by the three types of $L$ electrons were found to vary approximately as ${\lambda }^{2.56}$ for each of the five elements gold to bismuth. With this relation the coefficients were computed for a given wave-length. Their ratio $\tau \left(L_{\mathrm{I}}\right):\tau \left(L_{\mathrm{II}}\right):\tau \left(L_{\mathrm{III}}\right)$ (which is therefore independent of the wave-length) was found to be constant over the range 0.5 to 1.5A and to have approximately the same value for each of the five elements. The value of the ratio was found to be 19: 32: 49. This ratio also gives the relative numbers of photoelectrons ejected from the three $L$ shells by radiation of a given frequency. Ratios of $\tau \left(L_{\mathrm{I}}\right)$, $\tau \left(L_{\mathrm{II}}\right)$ and $\tau \left(L_{\mathrm{III}}\right)$ which are evaluated at their respective absorption edges $L_{\mathrm{I}}$, $L_{\mathrm{II}}$ and $L_{\mathrm{III}}$ were also determined. This ratio of $\frac{\tau \left(L_{\mathrm{II}}\right)}{\tau \left(L_{\mathrm{III}}\right)}$ was found to be approximately 0.45 for each element and is in good agreement with the value predicted by relativistic theory. The ratio $\frac{\tau \left(L_{\mathrm{I}}\right)}{\left[\tau \right(L_{\mathrm{II}})+\tau (L_{\mathrm{III}}\left)\right]}$ has been found theoretically only by means of a nonrelativistic treatment of absorption. The experimental value, 0.163, is not in good agreement with the predicted value.