X ray crystallography - interpreting my graph

In summary: These peaks are caused by the excitation of the anode electrons by the incident electrons. This produces characteristic x-rays which are then scattered by the crystal. The angles at which these peaks occur can be used to calculate the interplanar spacing using the Bragg equation.In summary, the conversation discusses a laboratory experiment involving crystallography and the use of a spectrometer with an unfiltered Molybdenum anode lamp. The main query is about the use of a continuous spectrum and the detection of bremsstrahlung. The solution involves looking up the spectrum for Molybdenum anodes and using the Bragg equation to calculate interplanar spacing.
  • #1
Old_sm0key
17
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Homework Statement


I am currently part way through a laboratory experiment that utilises basic crystallography to ultimately calculate lattice constants and structure factors for NaCl (we receive formal training in the next academic year via full treatment of von Laue, Bragg diffraction etc).
I have consulted a couple of recommended textbooks, but nothing addresses my concerns.
Our X ray spectrometer his an unfiltered Molybdenum anode lamp. The goniometer is geared to maintain the Bragg geometry (Geiger tube turns at twice angular speed of table).

The plot for scanning across angles for a NaCl crystal is shown below.

Now here is my major query:
Bremsstrahlung with Mo {k_alpha and k_beta} emission lines are incident on the NaCl.
  • What use it is having a continuous spectrum incident on the crystal? I thought standard practise is to attenuate with say a Zr absorber foil via the absorption principle?
  • Why is bremsstrahlung *detected* - I thought it is just produced by the Mo anode in etc X ray tube?
  • Not knowing precisely what each pair of peaks (of diminishing intensity) shows, I do not know how to calculate d_hkl from this plot
Kf8UF0N.png

Homework Equations


[itex]n\lambda =2d_{hkl}\sin \theta [/itex]

The Attempt at a Solution

 
  • #3
Old_sm0key said:
What use it is having a continuous spectrum incident on the crystal? I thought standard practise is to attenuate with say a Zr absorber foil via the absorption principle?
Depends on your application I think.
Old_sm0key said:
Why is bremsstrahlung *detected* - I thought it is just produced by the Mo anode in etc X ray tube?
It is produced in the x-ray tube and scattered in the NaCl crystal. Where is the problem?
Old_sm0key said:
Not knowing precisely what each pair of peaks (of diminishing intensity) shows, I do not know how to calculate d_hkl from this plot
You can look up the spectrum for Molybdenum anodes. There are two very prominent peaks.
 

What is X-ray crystallography?

X-ray crystallography is a technique used to determine the atomic and molecular structure of a crystal. It involves directing an X-ray beam at a crystal and analyzing the diffraction pattern produced by the X-rays as they interact with the crystal's atoms.

Why is X-ray crystallography important in scientific research?

X-ray crystallography is important because it allows scientists to determine the 3D structure of molecules, which is crucial for understanding their function and interactions. This information can be used to develop new drugs, study biological processes, and design new materials with specific properties.

What does the graph in X-ray crystallography represent?

The graph in X-ray crystallography represents the diffraction pattern produced by the X-rays as they pass through the crystal. It shows the intensity of the diffracted X-rays at different angles, which can be used to determine the positions of the atoms in the crystal.

How do you interpret the graph in X-ray crystallography?

To interpret the graph in X-ray crystallography, you need to identify the peaks and their corresponding angles. These peaks correspond to the diffraction from different planes of atoms in the crystal. From the peak positions and intensities, the atomic structure of the crystal can be determined using mathematical algorithms.

What are some limitations of X-ray crystallography?

One limitation of X-ray crystallography is that it requires a crystal to be formed, which may not be possible for some molecules. Additionally, it can only provide a static snapshot of the molecule's structure and cannot capture any dynamic movements. The technique also requires specialized equipment and expertise, making it inaccessible for some researchers.

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