Lec 3 Interactions

Question 1

3 types of interactions of x-rays with matter?

Answer 1

Scattering
Absorption
Attenuation

Question 2

3 types of interactions of x-rays at the atomic level?

Answer 2

Photoelectric absorption
Compton scattering
Coherent scattering

Question 3

Percentage:

No interaction
Coherent scattering
Photoelectric absorption
Compton scattering

Answer 3

9
7
27
57

Question 4

• Coherent scattering - Scatters from ______.
• Photoelectric absorption - Ejects _______ and ceases to exist; releases _______.
• Compton scattering - Ejects _________, both scatter
• No interaction - Passes through _______.

Answer 4

• atom
• inner electron; characteristic photon
• outer electron
• patient

Question 5

Change in direction of a photon without a loss of energy.

Answer 5

Scattering

Question 6

Deposition of energy, i.e. removal of energy from the beam (total loss of energy).

Answer 6

Absorption

Question 7

Reduction in the intensity of the main X-ray beam caused by absorption and scattering.

Answer 7

Attenuation

Question 8

• This process occurs when an incident photon interacts with an electron in an inner orbital of an atom in the patient.
• The incident photon loses all its energy to the electron and ceases to exist.
• The energy absorbed by the electron is expended to overcome the binding energy, and the remainder energy remains as the kinetic energy of the electron as it escapes the confines of its orbital.

Answer 8

Photoelectric absorption

Question 9

Percentage of photoelectric absorption

Answer 9

27%

Question 10

The electron that was interacted by the incident photon is termed ?

Answer 10

Recoil electron / photoelectron

Question 11

It is the basis of image radiographic information.

Answer 11

Photoelectric absorption

Question 12

The probability of photoelectric interaction is _____ proportional to the third power of the ______________ (Z) of the absorber, and _________ proportional to the third power of the __________ of the incident photon (E).

Answer 12

• directly = atomic number (Z)
• inversely = energy (E)

Question 13

Implications:
- Differential absorption provides radiographic contrast.
- Different degrees of radiopacity.

Answer 13

Photoelectric absorption

Question 14

Occurs when a photon interacts with an outer orbital electron.

Answer 14

Compton scatter

Question 15

Percentage of compton scatter?

Answer 15

57%

Question 16

Results in the loss of an electron and ionization of the absorbing atom

Answer 16

Compton scatter

Question 17

Ejected electron

Answer 17

Recoil electron

Question 18

Implications:
- Exposes operator
- Carry no useful information; degrades image by reducing contrast.
- Travel varying distances; exposes patient.
- Increases patient radiographic dose.

Answer 18

Compton scatter

Question 19

Coherent scatter is also known as? (3)

Answer 19

Rayleigh, classical, or elastic scatter

Question 20

May occur when a low-energy incident photon (<10 keV) interacts with a whole atom.

Answer 20

Coherent scatter

Question 21

No energy is transferred to the biologic atom and no ionizations are caused.

Answer 21

Coherent scatter

Question 22

• The biologic effects are insignificant.
• Has minimal impact on image degradation.

Answer 22

Coherent scatter