Principles of diffraction

Question 1

How are X-rays produced? (Page 5/6)

Answer 1

X-rays can be produced by accelerating electrons from a cathode to an anode using a high voltage, deceleration of electrons on hitting the anode gives off X-rays

They can also be produced when an outer shell electron fills an inner shell

Synchrotrons are another way to generate X-rays

Question 2

What is a monochromator’s function? (Page 6)

Answer 2

Uses Bragg diffraction to select different wavelengths by changing the angle of diffraction

Question 3

What does a diffractometer do? (Page 7)

Answer 3

Creates a diffraction pattern that can be scanned using a detector

Question 4

What does the diffraction pattern tell us when we don’t have a lens? (Page 16)

Answer 4

The diffraction pattern can be studied to devise which arrangement of atoms gave rise to that pattern (can tell us about the structure of the molecule)

Question 5

What is a motif in a crystal lattice? (Page 20)

Answer 5

A structure that is repeated at each position in the lattice to create the whole crystal

Question 6

What happens to the angle of diffraction (θ) as the plane spacing (d) gets smaller? (Page 19)

Answer 6

The angle of diffraction gets larger as they are inversely proportional: sin(θ) = nλ / 2d

Question 7

What happens to the diffraction vector (s) as the plane spacing (d) gets smaller? (Page 18)

Answer 7

Diffraction vector gets larger as they are inversely proportional: s = sin(θ) x H(Hypotenuse), s/H = sin(θ), s/H = nλ / 2d, as d increases s will get smaller

Question 8

How do you deal with negative values of a unit cell (eg. (-1,1,0)? (Page 23)

Answer 8

Draw the plane in the negative region and observe where the equivalent plane will be in the frame of the unit cell

Question 9

When drawing a diffraction vector where is it in relation to the planes? (Page 24)

Answer 9

Orthogonal (at 90 °) to the planes