Introduction

The experimental study of X-rays involves consideration of the methods of producing X-rays over a wide range of photon energies, methods of detecting the X-radiation and analysing it in terms of intensity, photon energy and polarization, and the effect of materials placed between source and detector. We have already seen that X-radiation is produced whenever a beam of charged particles encounters any target material, solid, liquid, or gaseous, and that it is also emitted by various processes during radioactive decay. The charged particles used in X-ray generators are normally electrons, but protons or alpha particles are readily available in accelerated beams, and cause X-rays to be produced when slowed down in a target. Accelerating voltages, for electrons or other particles, may range from a few hundred volts to many MV, and the photon energies of interest extend from this upper limit down almost to the ultra-violet region of the electromagnetic spectrum. X-ray detectors depend upon the ionizing qualities of the radiation (or, very occasionally, upon nuclear excitation), and include photographic emulsions, gas-filled devices (such as the ionization chamber, and Geiger and proportional counters), the scintillation counter, and the solid-state detector. Some of these detectors have an intrinsic ability to distinguish between photons of different energy, but often this energy resolution will need to be improved upon by the use of diffraction gratings, or by utilizing Bragg reflection from single crystals.