The absorption of monochromatic X-ray beams, of wave-length in the region 50 to 20 X -units, in lead, tin, copper, and iron

In a previous paper an account has been given of the measurement of the absorption of monochromatic X-ray beams of wave-length in the region 50 to 20x -units, in carbon and aluminium. The relation of the measured coefficient of absorption to the wave-Iength did not differ from that predicted by the Klein-Nishina formula by more than 1%. The method used in that experiment has been improved, and used to measure the absorption coefficients of lead, tin, copper, and iron for similar monochromatic beams. Because lead has been used very extensively for absorption measurements the primary aim has been to measure as accurately as possible the dependence of its absorption coefficient on the wave-length of the radiation. It has not been possible to make such accurate measurements on tin, copper, and iron, but enough data has been obtained to determine the variation of the photoelectric absorption coefficient per electron with the atomic number of the absorbing element, with fair accuracy, for radiation in this region of wave-lengths. Since these absorption coefficients may find considerable application, it is considered well to give a more detailed account of the method of measurement, so that an independent judgment of their reliability may be made.