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Join Date: Apr 2012
Posts: 9

CuKa Radiation

05/03/2012 12:31 PM


i am reading some articles about XPS ( X ray photoelectron spectroscopythere is kind of alpha-radiation that is named CuK alpha-radiation..is there anyone who has got any information about it ?

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Anonymous Poster #1
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Re: CuKa radiation

05/03/2012 12:34 PM
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Re: CuKa Radiation

05/03/2012 10:29 PM

As someone involved in x-ray fluorescence spectroscopy for many years, I can answer this. Firstly it is not "alpha radiation" which is something quite different (a particle consisting of 2 protons and 2 neutrons).

It's actually an x-ray of energy 8.04 keV emitted by copper when an electron from it's K-shell electrons (the inner orbital) has been kicked out by other incident radiation and been replaced by an electron from a higher orbital. Hence there is a copper K-alpha and copper K-beta x-ray. The K-alpha indicates that the electron has fallen from the next higher orbital (L-shell) while the K-beta is from 2 orbitals higher (M-shell).

All elements when exposed to x-rays or electrons in the range 300 eV to about 60 keV will be fluoresced in the x-ray region. The incident x-ray beam kicks out an inner orbit electron from an atom and departs as a "photoelectron." The "hole" created is instantly filled by another electron from a higher orbital. The loss in energy of that electron falling from the higher to lower orbit results in an x-ray being emitted. The energy (or wavelength, if you like) is very specific for each different element and is used to identify the presence of that element and it's concentration in a sample. Hence x-ray fluorescence spectrometers (XRF) and widely used an an analytical tool.

X-ray tubes frequently use copper as the "target" element because it has quite a high melting point and can be made very pure. Other common targets include rhodium, chromium and tungsten. A beam of electrons is focussed on the target, in an ultra-clean vacuum and produces the required x-ray radiation. From Cu, there will be 3 main x-rays energies emitted:

Cu K-alpha at 8.04 keV (strongest)

Cu K-beta at 8.9 keV (~8 times weaker)

Cu L-alpha at 0.93 keV (very weak)

Hence the Cu K-alpha line is frequently used in other x-ray instruments such as your XPS and also in X-ray Crystallography. The other 2 lines can be selectively filtered off to leave you virtually monochromatic 8.04 keV x-rays.

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