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Energy-Dispersive Detector Energy Calibration

Energy-dispersive detectors require calibration for both energy scale and fixed scattering angle, 2θ. The data is collected using a multichannel analyser with typically 4096 channels; the channel number, n, being approximately proportional to the energy of the measured X-ray photon, E. At very high energies, a non-linear behaviour is observed so that in practice a quadratic expression is used for the relationship between n and E:

E = a + bn + cn2

The quadratic coefficients, a, b, c, are obtained by measuring the channel number for certain well-defined energies. For the higher energies, γ-emitting radioactive sources, such as 241Am (59.5412 keV) or 57Co (122.0607 and 136.4736 keV), may be used as shown in the figure below:

calibration
You should note that the figure above represents the summed total of several energy calibration data sets, which are acquired separately for convenience. The other spectral lines in the figure are X-ray fluorescence lines, which are stimulated in various foils using a γ-emitting 241Am source, the complete assembly being known as a "dial source". Typical spectral lines for a few elements are identified in the expanded figure below:

calibration

The broad peak at approximately 50 keV next to the Tb Kβ1 peak is due to Compton scattering. A table of values for the fluorescence lines indicated above is provided below. A complete listing of K (and L) emission X-ray lines are available in the International Tables for Crystallography, Volume C, page 177-182 (or in the old volume III).

  Kα2 Kα1 Kβ1 Kβ2
Cu   8.042 keV  
  (1.54178 Å)  
Rb 13.377 keV 14.963 keV  
  (0.92688 Å) (0.82863 Å)  
Mo 17.446 keV 19.610 keV  
  (0.71069 Å) (0.63225 Å)  
Ag 22.108 keV 24.946 keV 25.459 keV
  (0.56083 Å) (0.49701 Å) (0.48701 Å)
Ba 31.820 keV 32.197 keV 36.382 keV 37.261 keV
  (0.38965 Å) (0.38509 Å) (0.34079 Å) (0.33275 Å)
Tb   43.745 keV     44.478 keV     50.399 keV     51.747 keV  
  (0.28343 Å) (0.27876 Å) (0.24601 Å) (0.23960 Å)

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© Copyright 1997-2006.  Birkbeck College, University of London. Author(s): Jeremy Karl Cockcroft