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RTE1613 Radiographic Physics > Unit 2: Interaction with Matter > Flashcards

Unit 2: Interaction with Matter Flashcards

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1
Q

What are the five types of interactions with matter?

A

coherent scatter
compton scatter
photoelectric effect
pair production
photodisintegration

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2
Q

Coherent scatter can also be called:

A

Thompson scatter or Unmodified scatter

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3
Q

describe Coherent scatter:

A

Interaction between the incident x-ray and a target atom that becomes excited. The atom releases this excess energy as a scattered x-ray photon that changes in direction

no energy transfer and no ionization occur

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4
Q

What scatter is of little importance to diagnostic radiology?

A

coherent scatter

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5
Q

describe Compton scatter:

A

interaction between incident x-rays and outer-shell electrons and ejects electron and ionizes atom

photon changes direction with a reduction in its energy

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6
Q

What is the ejected electron called?

A

Compton/recoil electron

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7
Q

In the energy transfer of Compton scatter, what retains most of the energy?

A

the scattered x-ray

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8
Q

define absorbed dose:

A

amount of energy that ionizing radiation gives to a given mass of matter (radiation absorbed by an object)

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9
Q

What are the three types of Compton scatter?

A

back
side
forward

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10
Q

describe back scatter:

A

photon scattered 180° perp. to beam, strikes the IR/pt and travels back toward the tube

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11
Q

What causes back scatter?

A

photon strikes an outer shell electron with a head on collision

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12
Q

Back scatter can contribute to:

A

additional patient dose

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13
Q

describe side scatter:

A

photon scatters straight off to the side

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14
Q

What causes side scatter?

A

photon strikes an outer shell electron on its outer edge

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15
Q

What is side scatter the main source of?

A

occupational dose in radiography and fluoro

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16
Q

describe forward scatter:

A

photon travels in a forward direction and strikes the IR

provides no diagnostic information (no anatomy represented)

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17
Q

What causes forward scatter?

A

photon grazes an orbital electron by hitting side of atom and changes in a different forward direction

barely gives up any of its energy

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18
Q

What is the type of scatter that reduces image contrast/noise?

A

forward

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19
Q

List the factors that affect production of Compton scatter radiation:

A

field size (collimation)
body part thickness
body part density
body part electron density
photon energy
?kVp

20
Q

What is the relationship between Compton scatter and field size?

A

larger field size = more Compton scatter (more noise and lower image contrast)

21
Q

what is the most effective way of reducing pt dose?

A

collimation

22
Q

What is the relationship between Compton scatter and body part thickness?

A

thicker part = more Compton scatter

compress thicker body parts

23
Q

What is the relationship between Compton scatter and body part density?

A

greater the density = greater the Compton scatter production

24
Q

T/F: atomic number of tissue does not effect the likelihood of Compton scatter.

A

true

25
Q

Why do more denser parts increase scatter?

A

atoms are packed more tightly, meaning more electrons leading to increase in scatter

26
Q

The greater amount of water present in tissue will produce a _________ amount of Compton.

A

greater

27
Q

What is the relationship between Compton scatter and kVp?

A

increasing kVp will increase Compton scatter

28
Q

Why do we use grids?

A

higher body parts require higher kVp settings, which will produce more scatter

29
Q

What do grids do?

A

clean up forward Compton scatter

30
Q

list the ways to reduce Compton scatter lowering image contrast:

A

lowest possible kVp
grids
smaller field size
air gap technique
compression

31
Q

describe the Photoelectric effect:

A

x-rays undergo ionizing interactions with inner-shell electrons that become totally absorbed by the K-shell electron

pt dose and absorption

32
Q

Photoelectric interaction produce secondary radiation through what?

A

cascading effect

33
Q

What must happen in order for the photoelectric interaction to happen?

A

incident x-ray energy must be equal to or slightly greater than the electron binding energy

34
Q

What are the factors that affect photoelectric effect?

A

kVp
body part thickness
body part density
atomic number tissue

35
Q

What is the relationship between the photoelectric effect and kVp?

A

increasing kVp -> increases photoelectric interaction due to increase in quantity

36
Q

increasing kVp will:

A

decrease diff. absorption

37
Q

What is the relationship between the photoelectric effect and body part thickness and density?

A

thicker and denser body parts -> increases chances of photoelectric interactions

38
Q

What is the relationship between the photoelectric effect and the atomic number of tissue?

A

atomic number increases -> photoelectric effect increases greatly

39
Q

increasing x-ray beam energy will result in:

A

overall increase all interactions

fewer avg. Compton interactions

much fewer avg. photoelectric interactions

more transmission through pt

40
Q

describe pair production:

A

photon escapes influence w/ orbital electrons and interacts w/ the nucleus

41
Q

what happens to the photon during pair production?

A

it disappears and is replaced with two electrons (positron and negatron)

42
Q

pair production requires a photon energy that is:

A

greater than 1.02 MeV

43
Q

describe photodisintegration:

A

photon escapes interaction w orbital electrons and becomes absorbed by nucleus

44
Q

What happens to the nucleus during photodisintegration?

A

nucleus enters an excited state and emits a nucleon or other nuclear fragment

45
Q

photodisintegration requires a photon energy that is:

A

10 MeV or greater

RTE1613 Radiographic Physics (9 decks)

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