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X-ray diffraction pattern from crystal?
To anyone who has done experiments in X-ray crystallography in the past.
We are bomarding copper with high energetic electrons, thus forcing it to emits the K-alpha and K-beta characteristic radiations ( X-rays) and some background. These are shone on and scattered by a crystal. We detect the intensity of the diffraction pattern as a function of the angle of declination of the crystal.
We get a graph with 2/3 sets of double peaks. This makes sense, since each doublet corresponds to the K-alpha and K-beta emission, and each set corresponds to when constructive interference occurs.
What I don't get, is why these peaks get lower with angle. That it, at large angle of declination of the crystal, we get less intense peaks. WHYYYYY?
ALso, could you please quote a reference, or sth OFFICIAL which is saying that? I've been looking all week but I haven't found anything.
2 Answers
- 8 years agoFavorite Answer
ZAF
Z=Atomic Number
A=Absorption
F=Fluorescence
CuKalpha = 8.6keV
Reduced peak intensity principally by absorption as X-ray leaves from inside crystal surface at higher angles. Increased path length increases absorption.
Additional:
Absorption
Absorption phenomena related to fluorescence effects have already been discussed.
Absorption also occurs related to the area of a powder specimen and depth of penetration of
the x-ray beam into the specimen. In general, with a Bragg-Brentano diffractometer, the
larger area of sample irradiated at low 2θ values have less depth of penetration. At higher 2θ
values, the irradiated area will smaller, but depth of penetration greater. In general, these
tend to be offsetting effects as related to diffracted intensity over the angular range of the
data collection. The calculated intensity will include a term for 1/µs where µs is the linear
absorption coefficient of the specimen.
Need to look under Quantitative analysis in X-ray diffraction.
If you think that the above section (quoted from a paper) is what you are looking for I can give the web address to you.
Me: operator of
X-ray and electron micro probe analyser (Jeol) with fully quantitative energy and wavelength dispersive analysis capability.
- ?Lv 45 years ago
You are improper. X-rays aren't mirrored from a crystal floor, they're diffracted. That is why it can be referred to as x-ray diffraction, strangely sufficient. Attempt to learn as a minimum the elemental facts before asking silly questions.