Table 8.8 Some typical crystals used in dispersive X-ray analysis
Crystal 2 d/nm Wavelength range/nm
Lithium fluoride (LiF) 0.403 0.0351–0.384
α-Quartz (SiO 2 ) 0.852 0.0742–0.812Pentaerythritol (PET) C(CH 2 OH) 4 0.874 0.0762–0.834Rubidium hydrogen phthalate (RAP) 2.612 0.228–2.492
o—C 6 H 4 (CO 2 H)(CO 2 Rb)The alternative approach to detection and analysis incorporates a solid state detector and a multichannel
pulse height analysis system. The crystals used are of silicon (of the highly pure intrinsic type), or the
lithium drift principle (p. 463 et seq.) is utilized. All emitted radiations are presented to the detector
simultaneously and a spectrum is generated from an electronic analysis of the mixture of voltage pulses
produced. Chapter 10 contains a more detailed account of pulse height analysis and solid state detectors.
Production of an X-ray spectrum in this way is sometimes known as energy dispersive analysis of X-
rays (EDAX) and where an electron microscope is employed as SEM-EDAX.
Filter based instruments lack flexibility and are generally employed for the routine analysis of specific
elements, whilst instruments utilizing a dispersing crystal have the greatest resolution. There is in
principle no limit to this resolution as the detector may be placed at a large distance from the
Figure 8.43
X-ray spectra of niobium and tantalum.