ABSTRACT
This chapter discusses the processes that occur when photons, electrons, ions and particles interact with materials. The penetration depth or mean free path of the incident beam determines the depth and volume of material that will be sampled. The penetration of photons shows considerable and dramatic variations between different types of material and photon energy or wavelength. The penetration of X-rays into a material shows less variation from one material to another than visible light and is easier to predict. Although a neutron is approximately one thousand times the mass of an electron and as a consequence is more particle like, it still possesses sufficient wave character to be diffracted by materials. While electrons are readily described as having a dual wave–particle character, their mass allows a considerable momentum, particularly when accelerated to several hundred kiloelectron volts in the transmission electron microscope, to be transferred.
