The Absorption of Ultra-Short X-Rays by Elements of High Atomic Number

Abstract

Employing a specially constructed two-crystal spectrometer and a 600-kilovolt x-ray machine, mass absorption coefficients have been measured, with an average probable error of 0.8 percent, for Pb(82), Ta(73), Sn(50), Ag(47), Mo(42), and Cb(41) in the wave-length range $30<\mathrm{}\lambda <185\mathrm{}$ X.U. Assuming the correctness of the Klein-Nishina formula for absorption due to scattering, the photoelectric absorption ${\tau }_a$ was calculated for the above elements. In the empirical equation ${\tau }_a=C_a{Z}^p{\lambda }^q$, $p$ increases from 3.51 to 3.88 as $\lambda$ decreases from 140 to 50 X.U., and $q$ increases from 2.60 to 2.80 as $Z$ decreases from 82 to 41. Agreements with data of other observers for Pb(82) are given. At 30 and 40 X.U., the present data for Pb(82) are about 10 percent higher than the theory developed by Hulme, McDougall, Buckingham and Fowler. New constants in Gray's empirical equation for ${\tau }_{\mathrm{Pb}}$ are suggested of: $a=\overline{3}.7321$, $b=1.03\mathrm{}$ and $c=0.44\mathrm{}$.