Actually when you ask someone.............about this, most often answer is: use a monochromator during the analysis..............actually i already tried but did not get any success.
Along with solution, can somebody give me the basic reason..........behind it? Actually, i did the analysis of my iron based oxide samples through various target say Cu, Co, Mo, etc.............But mostly Cu target shows fluorescence to the maximum extent.........but some of the sample(Iron based oxide) analysed by Mo also shows some extent of fluorescence.................
My question: fluorescence observed in the peaks of my samples are due to the samples or due to the instrumentation...........As some of my samples are mineral ore, so pls clarify my doubt?
Cu k-alpha energy =8046 eV > Fe K-edge energy = 7112 eV, so you will have Fe fluorescence in all cases you've mentioned. If you want to get rid of the fluorescence you can: 1) get Fe or Cr anode for your diffractometer; 2) use monochromator before the detector
For the very reason given above by Alexey Veligzanin, when performing XRPD (Powder) data collection of Fe-containing minerals, it is highly advisable to use an Fe-target (anti-cathode) tube. Since you are working on iron based oxide samples and mineral ore, you should follow this advice to avoid your pattern being coarsely affected by fluorescence.
The reason why you perhaps still see fluorescence is cause by the position of your monochromator. If you have a primary momochromator it doesnt help at all. You need to apply a secondary in front of the detector as Alexey pointed out.
@Romano: I have to admit that using another radiation like Co, Fe or Cr would be the best solution. Unfortunately, I do not know many people anymore who have more than one tube. No idea, why physics is ignored. I guess it is related to the believe, a monochromator will always help. Nobody is talking about the loss of intensity...especially when two monochromators are used...
The answers above are correct. I will just add/emphasize a few points.
"Primary monochromator" means on the incident beam. This will not reduce flourescence.
"Secondary monochromator" means on the diffracted beam side, just before detector. This is what you need to reduce flourescence signal.
Regarding other tubes:
Proto Manufacturing (www.protoxrd.com) makes tubes with any anode you want. The following anodes will be useful for avoiding flourescence in Fe: Ti (but less common becuase no beta filter), V, Cr (common), Mn (used a lot for stress measurements on Fe), Fe, Co. Any of those will work well with Fe-containing samples.
As special note on Mo anode. Although Mo radiation does induce flourescence in Fe, the energy difference between Fe Kalpha radiation and Mo Kalpha radiation is so great that properly set detector electronics and readily distinguish between the two, thus eliminating the flourescences signal, instead of stopping the flourescence itself. The energy difference between Fe Kalpha and Cu Kalpha is too small for most detectors to separate (detectors used for XRF can separate, but they are not commonly used for XRD).
To restate the general principle: you get lots of flouorescence when the energy of the Kalpha radiation incident on the sample exceeds the energy of the K absorption edge of the target or sample element. The closer the match, the more intense the flourscence.
The above discussion is significant and very practical reasoning and solution were given.. Regards
Alexey, if I good remember the secondary monochormator is good only for parallel beam geometry of diffractometer (with Sollers slits one on the incident beam, second on the diffraction beam) and with the point detector. Am I right?
Is it secondary monochromator helpful for other geometries, such as Bragg-Brentano? In my opinion: no. Am I right?
There are of course others solution for other systems, e.g. by discrimination of the energy for linear silicon detector, or as mentioned above different type of the X-ray tube.
The best solution is to use energy discriminate detector. U dont need to worry about fluorescence effect from ur samples because the signal are digitally filter - band pass filter. As well as removed the beta-filter or any monochromators so that the intensity can be maximized - simple instrument.
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