Absorption Measurements on Very Hard X-Rays

Citation

Blackburn, John Francis (1932) Absorption Measurements on Very Hard X-Rays. Dissertation (Ph.D.), California Institute of Technology. https://resolver.caltech.edu/CaltechTHESIS:02262024-225100622

Abstract

[Introduction] Many - perhaps most - measurements of x-ray absorption coefficients have been made with inhomogeneous radiation, using the "end radiation" method. This method possesses the great advantage of involving but little apparatus and a simple experimental technique, but the measurements are difficult to interpret and it is usually impossible to determine the relation between the apparent absorption coefficient as determined by this method and the monochromatic absorption coefficient. Moreover, there are many pitfalls for the experimenter concealed in this apparently simple method, and it is the purpose of this paper to point out some of these pitfalls.

If the published values of absorption coefficients obtained by this method are compared, it is found that there is in general little agreement among the values obtained by various experimenters under supposedly identical conditions, and that most of these values are much higher than the values computed from the formulae of Klein and Nishina, Richtmyer, and others. The lack of agreement, together with the fact that the present active development of tubes for very high voltages Will involve the taking of many new measurements by this method, has made it desirable to study the method in some detail, and this paper will discuss chiefly the process of "monochromatizing" radiation by filtration.

All of the experimental work reported herein was carried out at 550 kv. and the conclusions drawn from the work are to be regarded as applying strictly only to this type of radiation, namely, the continuous spectrum emitted by x-ray tubes working at 300 kv. and higher, although with suitable modifications they will also apply to softer radiation. They do not apply to measurements of absorption made with spectrographs, nor to methods' making use of fluorescent or characteristic radiation, or of absorption edges, such as the balanced filter method of P. A. Ross. Finally, they do not apply to spectra consisting largely or wholly of well separated sharp lines or groups of lines, such as gamma-ray line spectra. Within these limits, however, it is believed that the conclusions are at least qualitatively correct.

Thesis Files