X-Ray Interactions

Question 1

Linear attenuation coefficient represents

Answer 1

the fraction of photons that interact per unit thickness of a given material

Question 2

LAC only valid if

Answer 2

incident beam energy is monochromatic

Question 3

mass attenuation coefficient is obtained by

Answer 3

dividing the LAC by the density of the material

Question 4

Coherent (rayleigh/elastic) scatter

Answer 4

• xray as a wave
• no loss of energy or rad dose
• more likely in higher Z
• depends on photon energy, dominates lower energy x rays
• scatter angle can vary (small)
• sinusodial electric field, e- oscillate reradiate xray
• charged particle in electric field will move

Question 5

Compton (incoherent/inelastic) scatter

Answer 5

• particle like behaviour
• peak at same energy going through
• one of the most important
• some rad dose
• diff of lost energy between peaks
• no binding energy
• recoil electron through tissue, scatter gives energy

Question 6

compton scatter dependent on

Answer 6

energy, atomic number

Question 7

fluorescent yield

Answer 7

probability of emission of characteristic radiation to emission of an auger electron

Question 8

photoelectric absorption more likely in bone or soft tissue?

Answer 8

bone

Question 9

photoelectric process is more likely to occur if the incident photon energy is

Answer 9

just above binding energy of the electron

Question 10

if the incident photon energy is just under binding energy of the electron

Answer 10

it cannot be ejected as there is insufficient photon energy to overcome the energy that bind electron to nucleus

Question 11

100-800 keV

Answer 11

compton

Question 12

z component dependent

Answer 12

coherent and photoelectric

Question 13

10-30 kev

Answer 13

photoelectric

Question 14

1-8 kev

Answer 14

compton, no photoelectric, no coherent (a tiny bit at 1)