X-ray Generation and Properties
X-rays are electromagnetic radiations having energies in the range of 1 keV-100 keV. For diffration studies, short wavelenth X-rays in the range of few angstroms (1 keV-120 keV) are used. Because the wavelength of X-rays is comparable to the size of atoms, they are ideally suitable for assessing the structural information of materials .
X-rays are produced generally by either from X-ray tubes or synchrotron radiation. Most widely used X-ray source is from X-ray tube, on which X-rays are produced when high speed electrons collide with a metal target. As electrons collide with atoms in the target and slow down, a continuous spectrum of x-rays are emitted. The high energy electrons also eject inner shell electrons in atoms through the ionization process. When a free electron fills the shell, a X-ray photon with energy characteristic of the target material is emitted.
Common targets used in X-ray tube include Co, Cu and Mo, which are having wavelengths of 1.79 Å, 1.54 Å and 0.8 Å, respectively.
The energy " E " of a X-ray photon and it's wavelength (l) is related by the equation
E = hc/l
h = planck's constant
c = speed of light
An X-ray tube contains:
(i) a source of electrons
(ii) a high accelerating voltage
(iii) a metal target
Figure 1: Schematic cross section of an X-ray tube.