# Interaction of X and Gamma rays in matter

Questions, questions, questions... I hope some one can answer these questions. thank you. :)

1. Describe the process of Compton Scattering, explaining carefully how both attenuation and absorption of X-rays occur.

2. How does the process of Compton scattering of X-rays depend on the nature of the scattering material and upon X-ray energy? What is the significance of the process in radiographic imaging?

3. Explain why radiographic exposures are usually made with an X-ray tube voltage in the range 50-110kVp.

4. A parallel beam of monoenergetic X-rays impinges on a piece of lead. What is the origin of any lower energy X-rays which emerge from the other side of the sheet traveling in the same direction as the incident beam?

5. How would a narrow beam, of 100kV X-rays be changed as it passed through a thin layer of material? What differences would there be if the layer were (a) 1 mm lead (Z = 82, ρ = 1.1 x 104 kg m-3), (b) 1mm aluminum (Z = 13, ρ = 2.7 x 103 kg m-3)?

6. What factors determine whether a particular material is suitable as a filter for diagnostic radiology?

7. Discuss the advantages and disadvantages of using aluminum as a filter material in X-ray sets at different generating potentials.

8. The dose rate in air at a point in a narrow beam of X-rays is 0.3 Gy min-1. Estimate, to the nearest whole number, how many half-value thickness of lead are required to reduce the dose rate to 10-6 Gy min-1 Gy min-1. If H1/2 at this energy is 0.2mm, what is the required thickness of lead?

9. Explain what you understand by the homogeneity of an X-ray beam and describe briefly how you would measure it.

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Hootenanny
Staff Emeritus
Gold Member
Well, what do you think?

Well, I have some idea's and i don't know if they're right. Hopefully there are medical physicists here who can answer these questions. btw, i'm a 1st year MS Medical Physics Student... I'm not one of the bright one though...

I manage to answer the 1st,2nd and 3rd question but i don't know if it's right...

#1
--- Compton scattering is an inelastic scattering, where in the effect is like billiard balls that will collide each other. It usually happens when a photon hits a free electron. And for energy and momentum conservation, the intensity of the photon energy is attenuated and some of the energies were absorbed by the electron and then it is called the Compton electron.

#2

--- Compton scattering depends on the nature of the scattering material and X-ray energy because this 2 components are responsible for the radiographic image. For example if the scattering material has low half value layer (H1/2) and the X-ray energy is great then the image form is not good. This is because all photons has penetrated on the material. But if you have the right value of H1/2 and exact amount of X-ray energy then you will be able to form a better radiographic image.

#3

--- It is in that range because below 50 kVp would create a less energy of photon that would it would be less penetration of the radiation in the material and it would need much time for the material to be exposed. Above 110 kVp, though is is good because the time of exposure can be lessen, material would absorb too much radiation.

MixedWanton said:
Well, I have some idea's and i don't know if they're right. Hopefully there are medical physicists here who can answer these questions.
There's at least one medical physicist lurking around who can answer them. Just waiting to see your work and the answers you've come up with.