Workshop Tutorials for Technological and Applied Physics
QR12T: X-rays II- X-ray Interactions and Applications
A. Qualitative Questions:
1. X-rays are widely used in industry and in medicine for imaging. They can be used to find bone damage
and flaws in engine parts, and to investigate the structure of things too small to see with visible light.
a. Why is it possible to use x-rays to see inside things that we can’t see into with visible light?
b. X-rays can also be used to see things that are smaller than we could see with visible light. Explain
why this is possible.
c. When you have an x-ray taken, for example if you break a bone, why are some bits of the picture light
and others dark? Which areas have the higher absorption of x-rays, and why?
2. When x-rays scatter from a material we may observe Compton scattering.
a. What is the Compton effect? Use diagrams to illustrate your answer.
b. Why don’t we observe Compton scattering with visible light?
c. How is it possible for the photons to give up part of their energy when we know from the
photoelectric effect and other experiments that photons are particles and only a whole photon can be
absorbed, not just part of a photon?
d. During Compton scattering the x-ray transfers some of its momentum to an electron. If the x-ray has
momentum, does this mean that it has mass?
e. What is the difference between the Compton effect and the photoelectric effect?
B. Activity Questions:
1. X-ray pictures
Examine the x-ray films.
Why are some areas light and others dark? In which areas are more x-rays absorbed?
Why are more x-rays absorbed in these regions?
2. Diffraction patterns
Shine the laser light through the fabric.
What sort of pattern do you see?
How does the pattern change when you stretch the fabric horizontally?
What about when you stretch it vertically?
3. X-ray diffraction
Examine the x-ray diffraction pattern and try to match the peaks to the lattice spacings in the crystal.
How many peaks can you match?
What would you expect the pattern to look like if you had a more complex crystal structure?
The Workshop Tutorial Project –QR12T: X-rays II – X-ray Interactions and Applications
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C. Quantitative Questions:
1. An x-ray photon with a wavelength of 100 pm collides with an electron at rest and is scattered at an
angle of 90o.
a. What is the change in wavelength of the photon?
b. What is the kinetic energy of the electron?
c. How many head on ( = 180o) scattering events would be necessary to double the wavelength of a 100
pm x-ray?
2. X-ray diffraction is a widely used technique in science and industry. In industry it is used to look at
stress and strain of materials, particularly during manufacture, for example on turbine blades for aircraft.
It is also being used by researchers in Australia to look at changes to the structure of hair with breast
cancer, as a possible diagnostic tool.
a. Explain briefly how x-ray diffraction can give information about the structure of a material.
b. Why does stress on a material cause a broadening of the x-ray diffraction peaks?
An x-ray beam is incident on a salt (NaCl) crystal, which has an inter-planar spacing of 0.281 nm. The
second order maximum in the reflected beam is found when the angle between the beam and the surface
is 21o.
c. What is the wavelength of the x-rays?
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The Workshop Tutorial Project –QR12T: X-rays II – X-ray Interactions and Applications