The study of some phenomena observed with monochromatic X-ray beams.

Abstract

The mass absorption coefficients of a number of pure elements ( Beryllium, Carbon, Aluminium, Iron, Nickel, Copper, Zinc, Molybdenum and Palladium ) have been measured for pure beams of Copper K ∝, and Cobalt K ∝ radiation.
The monochromatic beams were produced by the selective reflection of these wavelengths from the X-ray beam emitted by a rotating anode X-ray tube by means of a powdered crystal focussing monochromator and were detected by Geiger tubes connected to pulse counting equipment.
An attempt was made to measure the fluorescent absorption coefficients of these metals, as well as their total mass absorption coefficients, which include the scattering coefficients. The values obtained were ( within the experimental error of these measurements) in agreement with the total absorption values, so that the part of the absorption coefficient due to the scattering of the X- rays is small for these wavelengths, and can be ignored in comparison with the fluorescent absorption. The measured absorption coefficients were in good agreement with those obtained by other workers, although they did not use such pure monochromatic X-radiation. Measurements were also made with a beam of Chromium radiation which was not monochromatic but consisted of the
Chromium K∝, wavelength contaminated by the white radiation from the X- ray tube. In this case, the mass absorption coefficient varied with the thickness of material irradiated, but by graphical analysis of the transmitted intensity curves,
the values at different wavelengths present in the beam could be determined. They were not as accurate as those carried out with the pure radiations.
The variation of the atomic absorption coefficients, calculated from the results, with wavelength and atomic number, was investigated, and an empirical absorption formula deduced. It was found that the fluorescent absorption
coefficient can be represented by a formula of the form XXXX where m and n are constants only over small ranges of Z and A• Different values have to be
assigned to m and n if we are to cover all the elements over a large wavelength range. The variations in the values of the exponents m and n are discussed in the light of the results of several investigators.
An empirical formula, which gives excellent values of the K absorption ratios (jump ratios), for most of the elements, is also deduced. It shows that they vary inversely as the square root of the atomic number. Lastl y, some approximate scattering mass absorption coefficients are deduced, and plotted to show their variation with atomic number and wavelength.

Date of Award	Sept 1953
Original language	English
Awarding Institution	University College of North Wales, Bangor
Sponsors	University Of Wales & Department of Scientific and Industrial Research
Supervisor	E A Owen (Supervisor)