ABSTRACT
There are several possible interactions between radiation and matter, but the most important are absorption, diffraction and scattering. Absorption occurs when the frequency of the radiation corresponds to a specific energy difference for transformation of the constituent molecules or atoms from one energy level to another; this forms the basis for the spectroscopic methods of polymer characterization described in Chapter 15. When the constituent molecules or atoms are organized into regular arrays, as in the crystalline state, radiation with a wavelength similar to the lattice spacings will be diffracted, this forming the basis for crystallography and the well-known Bragg diffraction of X-rays by crystalline solids which is described in Section 17.2.1. When the constituent molecules or atoms are in a disorganized state and the frequency of the radiation does not correspond to energy level differences, the radiation is scattered in all directions by the molecules or atoms.
