The Absorption of X-Rays of Wave-Length down to.08A

Abstract

Mass absorption coffiecients of C, paraffine, S and 16 metal elements from Al to U for wave-lengths.56 to.08A have been measured in continuation of previous ${\mathrm{work}}^{1}$ which covered most of these elements in the range.71 to.10A. The general radiation from a tungsten target (operated at voltages up to 200 kv) was dispersed by a crystal into an ionization chamber. By using Soller multiple slit collimators about ten times as great intensity was obtained as with a single slit of the same resolving power. The main results of the previous paper were confirmed and extended, especially the steady decrease in the "jump" of the absorption in going from the L to the K regions, as the atomic number increases. The scattering of paraffine wax is distinctly greater than that of C or Al, probably due to the richness of H in paraffine. The empirical formula $\frac{\ensuremath{\mu}}{\ensuremath{\rho}}=\frac{C{\ensuremath{\lambda}}^{2.92}{N}^{4}}{A}+\frac{\ensuremath{\sigma}}{\ensuremath{\rho}}$, applied to the experimental results gives values of $\frac{\ensuremath{\sigma}}{\ensuremath{\rho}}$ which increase in general with atomic number, becoming about 1 for the heavier elements, W to Bi. The values of $C$ obtained are.0132 for the K series and.00181 for the L series; these give calculated values which agree within 5 percent with the experimental. Experiments with end-filtered high voltage rays. Without collimators or crystal, the ionization chamber in the path of the direct beam of rays filtered through 1 cm tin and 2 cm aluminum, showed increased ionization when a carbon block was interposed, but when two Soller collimators were used with planes crossed so as to eliminate all oblique rays, normal absorption coefficients were obtained corresponding to.075A. This method may be useful for the shortest rays.