Chemistry Reference
In-Depth Information
X-RAY SOURCE AND OPTICS
3.1 X-RAY GENERATION AND CHARACTERISTICS
A variety of X-ray sources, from sealed X-ray tube and rotating anode generator
(RAG) to synchrotron radiation can be used in X-ray diffraction. The sealed tube
generator and rotating anode generator produce X-ray radiation with the same
physical principle. Electrons are emitted from the cathode and are accelerated by
high voltages between the cathode and anode. The anode is made of a selected metal,
so it is also called metal target. When the electron beam hits the target, X-rays are
produced and radiate in all directions. This section gives a brief introduction to X-ray
sources and X-ray optics related to two-dimensional X-ray diffraction. The history
and principle of X-ray generation can be found in many literature [1,2].
3.1.1 X-Ray Spectrum and Characteristic Lines
X-rays generated by sealed tube or rotating anode generators have a spectrum
(intensity versus wavelength) as shown in Figure 3.1. The polychromatic radiation
consists of continuous radiation and a number of discrete characteristic lines. The
continuous radiation is also called white radiation or Bremsstrahlung. The shortest
wavelength (highest energy) in the Bremsstrahlung is called the short wavelength
limit l
SWL
, which is given by
12400
V
l
SWL
¼
ð3
:
1Þ
