SCATTERING

Most of the light that enters our eyes has been scattered and when we see objects we see them because of the diffuse scattering of light they produce. Even the sky is blue because of how it scatters sunlight. But scattering is also an important mechanism for observing very small objects. As a classic example, recall how Lord Rutherford unveiled the internal structure of the atom by studying the scattering pattern of alpha particles directed at gold atoms. The abnormally large number of particles backscattered by these gold atoms pointed to the existence of a small, but very dense, center which we now refer to as the nucleus.

In the next chapter, we develop the basic framework for the scattering of waves by condensed matter by looking at how electromagnetic waves scatter from the electrons contained in the particles. Although this is strictly relevant only for the scattering of X-rays and visible light, much of the formalism that develops will apply equally to other waves, including particle waves (electrons or neutrons) that interact with things other than electrons. In the following chapter (Chapter 6), we look at how X-rays scatter from crystals. There we will find scattering that is reminiscent of how visible light is scattered by a diffraction grating in that the scattered radiation exits as a set of discrete beams. This discrete (Bragg) diffraction is contrasted in Chapter 7 by the continuous pattern of scattering produced by glasses or liquids.