Ch 9 X-ray Interaction With Matter

Question 1

x-rays interact with matter in 5 ways:

Answer 1

1) coherent scattering
2) Compton scattering
3) photoelectric effect
4) pair production
5) photodisintegration

Question 2

absorption determines:

Answer 2

the degree of contrast of an x-ray image

Question 3

electromagnetic radiation interacts with structures that are:

Answer 3

similar in size to the wavelength of the radiation

Question 4

the higher the energy of an x-ray the ______

Answer 4

shorter its wavelength

Question 5

x-rays with energies below ____ interact with matter by _____

Answer 5

energies below 10 keV interact with matter by coherent scattering

Question 6

in coherent scatter the incident x-ray interacts with:

Answer 6

a target atom causing it to become excited, immediately releasing the excess energy as scatter

Question 7

the released scatter x-ray has a wavelength ____

Answer 7

equal to that of the incident x-ray (λ=λ’) and therefore equal energy

Question 8

the result of coherent scatter is ____ ; there is no ____ and therefore no _____

Answer 8

a change in the direction but not the energy of the x-ray; there is no energy transfer and therefore no ionization

Question 9

*coherent scattering is:

Answer 9

of little importance to diagnostic radiology

Question 10

Compton scattering is when there is interaction with:

Answer 10

outer shell electrons that not only scatters the x-ray but reduces its energy and ionizes the atom as well

Question 11

the energy of the Compton scattered x-ray is equal to:

Answer 11

the difference between the energy of the incident x-ray and the energy of the ejected electron

Question 12

Compton Effect

Ei =

Answer 12

Ei= Es + (Eb+Eke)

Ei: energy of incident x-ray
Es: energy of scattered x-ray
Eb: electron binding energy
Eke: kinetic energy if the electron

Question 13

during Compton scattering most of the energy is divided between ______ but the ______ retains most of the energy

Answer 13

the scattered x-ray and the Compton electron but the scattered x-ray retains most of the energy

Question 14

Compton scattered x-rays can deflect in __ direction including _____

Answer 14

any direction including 180 degrees from the incident x-ray

Question 15

at a deflection of 0 degrees ____ energy is transferred

Answer 15

no energy

Question 16

as the angle of deflection increases to 180 degrees:

Answer 16

more energy is transferred to the Compton electron

Question 17

at 180 degrees of deflection the scattered x-ray retains:

Answer 17

at least 2/3 of its original energy

Question 18

backscatter radiation is:

Answer 18

x-rays that scatter back in the direction of the incident x-ray beam

Question 19

the probability of Compton scattering decreases as:

Answer 19

x-ray energy increases

Question 20

*the probability of Compton scattering is _____ to x-ray energy and independent of ______

Answer 20

inversely proportional to x-ray energy and independent of atomic number

Question 21

the probability of Compton scattering does not depend on _____

Answer 21

the atomic number of the atom involved

Question 22

*Compton scattering reduces ____

Answer 22

image contrast

Question 23

with the PHOTOELECTRIC EFFECT the x-ray is not _____ but ______; ionization of _____ electrons occurs

Answer 23

not scattered but totally absorbed; ionization of inner shell electrons occurs

Question 24

*the photoelectric effect is _____

Answer 24

total x-ray absorption

Question 25

(Bremsstrahlung/Characteristic) x-rays are produced after a photoelectric interaction

Answer 25

Characteristic

Question 26

the electron released in the photoelectric effect has an energy equal to:

Answer 26

the difference between the binding energies of the shells involved

Question 27

the probability of photoelectric effect is: (energy)

Answer 27

inversely proportional to the third power of the x-ray energy (1/E)³

Question 28

photoelectric interaction cannot occur unless:

Answer 28

the incident x-ray has energy equal or greater than the electron binding energy

Question 29

the probability of photoelectric effect is: (Z)

Answer 29

directly proportional to the third power of the atomic number (Z) of the absorbing material

Question 30

photoelectric interaction is more likely to occur with _____

Answer 30

high-Z atoms

Question 31

pair production involves:

Answer 31

one positive and one negative electron (an electron pair)

Question 32

*pair production does not ______ because it requires _____

Answer 32

does not occur in x-ray imaging because it requires 1.02 MeV

Question 33

*photodisintegration does not _____ because it required ____

Answer 33

does not occur in x-ray imaging because t requires 10 MeV

Question 34

*differential absorption occurs because of:

Answer 34

Compton scattering, photoelectric effect, and x-rays transmitted through the patient

Question 35

*differential absorption increases as the ____

Answer 35

kVp decreases

Question 36

at low energies ____ is more common, at high energies ____ is more common

Answer 36

photoelectric, Compton scatter

Question 37

*the interaction of x-rays with tissue is proportional to the:

Answer 37

mass density of the tissue

Question 38

*probability of Compton scatter is _____

Answer 38

inversely proportional to the x-ray energy (1/E) and has no relation to atomic number

Question 39

*probability of photoelectric effect is _____

Answer 39

inversely proportional to the third power of x-ray energy (1/E³) and directly proportional to the third power of the atomic number (Z³)

Question 40

*photoelectric involves ___ electrons and has a ____ binding energy

Answer 40

inner shell electrons and has a higher binding energy

Question 41

*Compton scatter involves ____ electrons and has a ____ binding energy

Answer 41

out shell electrons and has a lower binding energy

Question 42

*Coherent = _____ = _____ = ______

Answer 42

Coherent = Classic = Thompson = Raleigh

Question 43

*in Compton the wavelength entering is _____ than the exiting wavelength

Answer 43

shorter

Question 44

*in coherent scattering the entering wavelength is _____ tot the exiting wavelength

Answer 44

equal to

Question 45

*the exiting wavelength in Compton scattering ____

Answer 45

changes direction

Question 46

*in photoelectric effect there is a _____ but no _____

Answer 46

is a entering ray but no exiting ray (is absorbed)

Question 47

*probability of Compton scattering decreases as _____ increases

Answer 47

energy

Question 48

*logarithmic scales allow you to:

Answer 48

plot a larger scale in a smaller area

Question 49

*logarithmic change of 0.3 is:

Answer 49

2 (equal to doubling the mAs)