Characteristic X-Rays
Definition
Sharp emission lines produced when an inner-shell vacancy in an atom is filled by an outer electron. Their energies are element-specific (Moseley's law) and form the basis of XRF identification.
- Cause
- Inner-shell electron vacancy filled by outer electron
- Property
- Element-specific emission energy
- Governing law
- Moseley's law
- Application
- Basis of XRF identification
Common questions
Why does element-specificity make characteristic X-rays useful for XRF?+
Because each element emits its own set of sharp energy lines, an XRF spectrometer can identify which elements are present in a sample by matching the observed emission energies against known values, without needing to consume or dissolve the sample.
How do characteristic X-rays differ from the continuous background seen in the same spectrum?+
The continuous background, or bremsstrahlung, arises from electrons decelerating across a range of energies and carries no element-specific information, whereas the sharp characteristic lines sit on top of it and are what analysts actually read for identification.
Related terms
- Anode Target
- The metal block (commonly Cu, Mo or Rh) that electrons strike inside an X-ray tube to produce the X-ray beam. Choice of...
- Bragg's Law
- nλ = 2d sin(θ). A monochromatic X-ray beam diffracted off the parallel lattice planes of a crystal produces constructive interference only at...
- Continuous (Bremsstrahlung) Radiation
- Smooth background X-ray spectrum produced when high-energy electrons decelerate in the anode. Element-independent. The 'hump' under the characteristic lines.
- D-Spacing
- The perpendicular distance between adjacent parallel planes of atoms in a crystal lattice, measured in angstroms or nanometres. Each set of planes...
- EDXRF
- Energy-dispersive X-ray fluorescence. A solid-state detector resolves the entire emission spectrum at once by photon energy. Cheap, portable, faster.
- K-Alpha Line
- The characteristic X-ray emitted when an electron drops from the L-shell to fill a K-shell vacancy. Brightest line for most elements; the...
- WDXRF
- Wavelength-dispersive X-ray fluorescence. An analyser crystal disperses fluorescence by wavelength (Bragg's law again). Slower, costlier, much higher resolution.