The copper Kα doublet, comprising Kα1 and Kα2 X-ray lines, is generated in an X-ray tube through a series of steps. Electrons, emitted by thermionic emission from a heated cathode, are accelerated towards the copper anode. Upon collision with copper atoms in the anode, these high-energy electrons cause inner-shell ionization, particularly in the K-shell. This process results in the creation of a vacancy in the K-shell, leading to an excited state of the atom. To regain stability, outer-shell electrons move to fill the vacancy, releasing energy in the form of X-rays. Kα corresponds to the transition from the L shell to the K shell, Kβ corresponds to the M shell to K shell transition, and Kγ corresponds to the N shell to K shell transition, each resulting in the emission of X-rays with distinct energy levels. The closely spaced Kα1 and Kα2 X-ray lines are a result of different electron transitions within the inner and outer electron shells. These two X-ray lines are closely spaced because generally the energy levels of electrons residing at a higher shell is not identical. They have slightly different binding energies, resulting in two X-ray lines with slightly different wavelengths.
Dear Shruti Sreeram ,
sorry, but let me clearify: there is only one K-shell level, but there are three L shell levels; i.e. LI, LII and LIII.
The electron transition from the LIII shell will result in the release of a K-alpha1 fluorescence photon and the transition from the LII shell will release the K-alpha2 photon. They are 'closely spaced' in energy and/or wavelength as already mentioned by Souvik Bhattacharjee.
For details please see for example Fig. 1 of :
https://www.ld-didactic.de/literatur/hb/e/p6/p6362_e.pdf
So far the production of the Cu K-alpha doublet in the x-ray tube spectrum is described.
The split of the diffraction peaks into K-alpha1 and K-alpha2 doublets is due to the Bragg law (lambda = 2*d*sin[theta]), which for fixed lattice plane spacings d, assigns each wavelength lambdaK-alpha1 and lambdaK-alpha2 to a special theta (or 2theta) position the XRD pattern. In most of the cases the doublet peaks overlap strongly; see for example page 8 of
http://prism.mit.edu/xray/introduction%20to%20xrpd%20data%20analysis.pdf
Best regards
G.M.
Thank you so much for your valuable inputs Souvik Bhattacharjee and Gerhard Martens
As @Gerhard show, there is also a weak K-alfa 3, but it is covered by two other strong lines. Sometimes, as in Topas, it has been considered in Refinement.
Dear Armand Budzianowski ,
sorry, but I have never seen or heard from a K-alpha-3 line.
There might be a typing error; K-beta-3 is a line which is assigned to the electron transition from the M3 to the K level:
see for example:
https://www.sciencedirect.com/topics/medicine-and-dentistry/characteristic-x-ray
But you are right; some times the beta line is considered in the refinement.
In the experiment one uses
a) ß-blocker (filters) to reduce the ß based XRD peaks,
or
b) a monochromator in front of the detector
or
even an energy dispersive detection to get rid of these XRD peaks and the fluorescence background.
Best regards
G.M.
What about the transition of the electron from L1?
http://dx.doi.org/10.13140/2.1.3837.5362
It is so small that it does not affect qualitative XRD analysis.
You are right; there is the LI to K transition, but it is a 'vorbidden' one, so the line intensity will be quite small.
I just had a look at the copy of my Bearden X-Ray Wavelength tables and found an entry for Tungsten (but not for Copper):
Designation: K LI 0,21592A and 57,42keV; and adjacent to that entry there is a hand written note done by myself via pencil: 'K-alpha-3';
thus some time ago I apparently had already 'contact' with respect to a K-alpha-3 line; but I forgot that issue and do not remember the context...
After a short search for' K alpha 3' I found an interesting paper:
Article The characteristic radiation of copper K α 1,2,3,4
but unfortunately without full-text...
Best regards
G.M.
Gerhard Martens , in fact there are indeed Cu Kalpha3,4 lines, and even some hypersatellite lines, which can be seen in XRD patterns of good monocrystals. You can find details here: https://nvlpubs.nist.gov/nistpubs/jres/109/1/j91deu.pdf
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