Hi there, I'm an instructor teaching a Physics course for Radiography students designed for students with little to no Physics background. In prepping the course, I've come up with a couple of questions that are bothering me and hope someone here can be of assistance. My questions pertain to x-ray production in radiography which is generally accomplished by firing beams of electrons at a metal target, generally made of Tungsten or an alloy of Tungsten. The resulting spectrum of x-rays is then described in terms of Bremsstrahlung and Characteristic x-ray production mechanisms. Any Radiography Physics texts I've come across describe Characteristic x-ray production by invoking essentially the Bohr model of the atom, wherein x-rays are produced by an electron in a higher shell dropping down to a lower shell in the atom. It is claimed that this model explains why characteristic x-rays show discrete emission lines in the spectrum, with energies defined by the differences in the electron binding energy between the shells. My belief is that this simplified explanation would be strictly only true for isolated target atoms, not for x-ray emission from the solid anode consisting of a large number of atoms. I've always qualitatively thought from my (very limited) understanding of solid state physics, that electron energy levels in a solid metal were better understood in terms of nearly continuous energy bands. My question then is how to reconcile the simple Bohr model description of characteristic x-rays with the presumably more complicated situation in a solid metal. Here are my questions: 1. In an actual x-ray spectrum from a metal target, characteristic radiation production is visible as a set of distinct peaks. Does each peak correspond to a photon of a single wavelength (i.e. are the peaks monoenergetic?), or does each peak correspond to a narrow range of energies (corresponding to transitions from a range of energy levels between bands), so that the peak appears to be monoenergetic without truly being so? My feeling is that it must be the latter, but I can't find a good reference source that addresses this 2. In looking up x-ray spectra data, characteristic line data are often provided for elements. I assume that these must be for isolated atoms of elements and not a large collection of atoms in a crystal lattice? 3. Is there a good reference paper or text that addresses some of these points that doesn't require extensive knowledge of solid state physics to parse? Thanks for your time. Chris.