Properties Of X-rays

Question 1

What is intensity?

Answer 1

• The intensity of a beam is defined as the the amount of energy passing through a given area that is perpendicular to the direction of radiation travel in a given unit of time.
• energy flowing through 1m x 1m in one second.
• As you get further away from a source of radiation the intensity reduces.

Question 2

What does Inverse Square Law state?

Answer 2

• The inverse square law states that the intensity of the radiation from a source varies inversely as the square of the distance from the source.

I proportional to 1/d2

Further away = less Intense
Closer = more intense

Works for dose and dose rate

Question 3

What are the 3 possibilities of interactions with matter?

Answer 3

• Attenuation
• Scattter
• Nothing

Question 4

What is Attenuation?

Answer 4

• To weaken or reduce in force, effect, amount or value.
• Different materials attenuate the beam differently.
• Attenuation in Bone > Soft tissue.

Question 5

What is the Beer Lambert Law?

Answer 5

It =I0e-ut
- It = transmitted intensity
- I0 = original intensity
- e = Euler’s number
-u = Linear attenuation coefficient
- t = Thickness

Linear Attenuation Coefficient

Bone 0.528
Muscle 0.237
Fat 0.185
Air 0.0004

Question 6

What is absorption good for?

Answer 6

• Therapy
• Imaging

Question 7

What is Scattering and what is it bad for ?

Answer 7

• To change direction
• Bad for Therapy
• Bad for Imaging

Scatter can be removed by a grid

Question 8

What is the importance of the energy of the beam?

Answer 8

• The higher the energy of the beam the more penetrating the beam.
  Also, the deeper the photons penetrate.

Question 9

How is energy dependent on interactions?

Answer 9

• Low energy (keV) dependent on atomic number and density.
  (Z3 & ρ)
• High energy (MeV) dependent on just density. (ρ)

Question 10

What is Ionisation?

Answer 10

• Ionisation occurs when some forms of radiation have sufficient energy to interact with atoms and ‘eject’ their orbital electrons.
• Such atoms (or the molecules that they form) can then be rendered unstable and reactive with consequent effects.
• This is the basis of the biological effect of ionising radiations such as x and γ rays.