The Absorption of theKαLine of Carbon in Various Gases and its Dependence upon Atomic Number

A description is given of the apparatus and methods used in a photographic investigation of absorption coefficients for the Kα line of the carbon (λ=44.6A) in different gases and in gold leaf. The mass absorption coefficients, μρ, found were as follows: He, 3600: CO₂, 4780: N₂, 3850: O₂, 5765: Ne, 13100: A, 45700: Kr, 31800: Xe, 6740: Au, 12500. Some of the atomic absorption coefficients (μₐ) derived from these values on the assumption that the absorption is independent of chemical combination are as follows: C, 0.44×{}10^-19: N, 0.89×{}10^-19: O, 1.52×{}10^-19: Ne, 4.36×{}10^-19: The wave-length of the Kα line of carbon lies between the K and LI absorption limits of these elements. The values of logμₐ when plotted against $logZ$ fall upon a straight line whose slope is 4.4. Hence in this wave-length region this should be the value of p in the equation τₐ=CλⁿZᵖ, provided that λK<λ<λL. The results of extrapolating current x-ray formulas to this wave-length are given and the values of μₐ so obtained are, in general, considerably too large. Since the exponent of Z in the above equation is found experimentally to be as large or larger than in the case of ordinary x-rays it appears that the proper exponent of λ may be considerably less than 3.