The Absorption Coefficient of Hard Gamma-Rays

Citation

Chao, Chung-Yao (1930) The Absorption Coefficient of Hard Gamma-Rays. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ZG7Q-QN03. https://resolver.caltech.edu/CaltechTHESIS:03092011-115217519

Abstract

The relation between the frequency of hard radiations and the absorption co-efficient is not experimentally well established at the present time. In the following work the absorption coefficient of γ-rays of ThC" is carefully investigated owing to their homogeneity.

As a result, the observed absorption coefficient of light elements is found to agree fairly well with the theoretical formula of Klein and Nishina. Running from low to high atomic numbers, the absorption per electron is, however, found to increase continuously. This was not noticed before because it was usually covered by the photo-electric absorption of the soft components in a non-homogeneous beam. Furthermore, in some cases emphasis was given to the mass absorption coefficient which is exceptionally high for the hydrogen compounds, consequently the characteristic of the continuous increase of the absorption coefficient per electron was neglected.

In order to interpret this anomalous absorption, several scattering experiments are carried out. The forward scattering can be accounted for by the assumption that all the external electrons behave as if they are free in high frequency radiations around a few x-units. Theoretically the part of the anomalous absorption of heavy elements might be due to the scattering of electrons inside the nucleus or that of tightly bound electrons. The fact that, although such a process does not contribute much scattering in the forward direction its contribution in large scattering angles may become important is also indicted in the experiment.

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