There are so many target materials which can be used as X-ray source in powder XRD system, then why the most of XRD system uses Cu metal as source? What is the rationality behind this preferential favor?
Dear Ravi Nandan ,
there are may reasons:
a) energy wavelength of Cu K-alpha; according to the Bragg law a quite broad range of d spacings can be accessed in also a quite accessable theta range,
b) x-ray fluorescence yield for Cu K-alpha is quite high compared to the bremsstrahlung background,
c) thermal conductivity of Cu for removing the power (heat) from the x-ray focus is outstanding,
d) machinability of Cu is excellent
Best regards
G.M.
Dear Ravi Nandan . See the following useful link: http://pd.chem.ucl.ac.uk/pdnn/inst1/xrays.htm
Also check please the following useful link; https://www.researchgate.net/post/Why-mainly-Cu-Kalpha-radiation-is-used-in-XRD-why-not-other-elements-and-what-is-the-reason-for-using-Kalpha-radiation-why-not-Kbeta
Sorry, Aref Wazwaz ,
but
a) your first mentioned link does not work, and
b) your second link (Chapter on X-Ray Techniques) does not at all deal with the special question of Ravi Nandan from above...
Ravi Nandan don’t worry dear , I will search for you another good ones . Wish you the best always.
Dear Dr. Nandan,
Cu as a X-ray source is preffered over other sources such as Co or Mo because of its high intensity of Cu (Ka) than Kb which surely needs to be filtered out. Because of its high wavelength and intensity, it is the preffered one. In addition, it does not give the elevated background as compared to other sources.
Dear Maninder Singh ,
sorry, but it is characteristic for all elements being able to emit K-beta radiation, that the K-alpha intensity is larger than that of the K-beta.
According to the attachment the K-alpha to K-beta ratio is about 1/0,13~7,7 for Co (Z= 27) as well as for Cu (Z=29) and about 1/0,19 ~ 5,3 for Mo (Z=42).
So Cu is not preferred with respect to the K-alpha to K-beta intensity ratio.
Bremsstrahlung background goes with Z. Here low Z elements should be preferred. Thus for Cu the situation is not the best, but better than that of high Z elements.
As of why Cu tubes are the default I think Gerhard Martens is spot on. An additional factor could also be as simple as economy of scale: it is mass produced more efficiently (my guess).
However , in selecting an x-ray source it is also worth considering the following:
For quantitative XRD analysis the X-ray wavelength must be carefully considered due to microabsoption effects in the sample, and it is not uncommon to have several different source wavelengths to change around as the sample composition requires.
For example, if your sample contains light element oxides with iron silicide particles (as in industrial ferrosilicon slags) you will have problems quantifying the sample using a Cu tube due to the disproportionate absorption of Cu Ka radiation by iron. Changing to Co or Cr radiation will greatly reduce the problem.
X-ray mass absorption coefficients for various source wavelengths are excellently visualized at webelements: https://www.webelements.com/periodicity/x_ray_mass_abs_Cu_K/
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