An Overview: Concepts, Units, and the Bohr Atom

Abstract

Our understanding of the structure of atoms and atomic nuclei is based on scattering experiments. Such experiments determine the interaction of a beam of elementary particles—photons, electrons, neutrons, ions, etc.—with the atom or nucleus of a known element. (In this context, we consider all incident radiation as particles, including photons.) The classical example is Rutherford scattering, in which the scattering of incident alpha particles from a thin solid foil confirmed the picture of an atom as composed of a small positively charged nucleus surrounded by electrons in circular orbits. As these fundamental interactions became understood, the scientific community recognized the importance of the inverse process—namely, measuring the interaction of radiation with targets of unknown elements to determine atomic composition. Such determinations are called materials analysis. For example, alpha particles scatter from different nuclei in a distinct and well-understood manner. Measurements of the intensity and energy of the scattered particles provides a direct measure of elemental composition. The emphasis in this book is twofold: (1) to describe in a quantitative fashion those fundamental interactions that are used in modern materials analysis and (2) to illustrate the use of this understanding in practical materials analysis problems.