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Dosimetry Physics 1 > Review Exam 1 > Flashcards

Review Exam 1 Flashcards

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1
Q

Define Exposure

A

of ionization produced in air

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2
Q
  1. Photons passes thru air and liberate electron through photon interactions.
  2. Electrons will then cause ionizations (anions and cations
  3. Ion collection plate with voltage applied to have anions go to the positive side and cations go to the negative side)
  4. This starts occurrent and a charge of either sign can be measured with an electrometer.
A

Ion chamber

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3
Q

Explain how an ion cahmber works

A
  1. Photons passes thru air and liberate electron through photon interactions.
  2. Electrons will then cause ionizations (anions and cations
  3. Ion collection plate with voltage applied to have anions go to the positive side and cations go to the negative side)
  4. This starts occurrent and a charge of either sign can be measured with an electrometer.
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4
Q

How does low air density affect ion chamber readings?

A

low reading
because air molecules are more spread out (less density) at higher temps

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5
Q

What air conditions would cause a high reading for an ion chamber (2)

A

high density, Low temp

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6
Q

List FAC corr factors: (3)
Which correction factor is only used if it is a secondary chambers calibrated against FAC chamber?

A
  1. Air density changes
  2. Ion recombination
  3. Air attenuation of photons
    calibration factors
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7
Q

What has a collection volume .6cm^3

A

Farmer

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8
Q

What are the 3 electrodes of a farmer chamber?

A

Central, guard, thimblewall

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9
Q

What does the central electrode do in a farmer chamber?

A

Collector

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10
Q

What does the guard electrode do in a farmer chamber? (4)

A

Insulator
prevents leakage
defines collection volume
prevents contamination

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11
Q

What chamber(s) use(s) a build up cap?

A

Thimble chamber & farmer chamber

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12
Q

What is a solid air equivalent shell (like a foam material)

A

Buildup cap

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13
Q

What does a bulidup cap do?

A

Creates CPE in the buidup region to allow for accurate measurement in this region

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14
Q

Why is it hard to measure dose in the build up region?

A

Steep gradient that can cause very inaccurate measurements if only off by a mm

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15
Q

What measures dose in the build up region (2)

A

Parallel plane/plate/pancake & extrapolation chamber

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16
Q

Used for in vivo (2)

A

TLD & diode

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17
Q

When positive and negative ions recombine the result in a charge created that never reaches collecting electrode

A

Ion recombination

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18
Q

Bias voltage approx ___ V does what?

A

300
helps reduce ion recombination

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19
Q

Ideal characteristics: (8)

A

no energy dependence
sensitivity
no saturation limit
spatial resolution
effective water equivalent Z (tissue eq)
no directional dependence
min ion recombination
reusable
quick read-out
inexpensive

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20
Q

Fricke dosimeter uses what to measure change?

A

Spectrophotometer

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21
Q

TLD most commonly uses what material?

A

LiF

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22
Q

Electrons excited, become trapped in conduction band, when heated they are released and recombine in valence band, and release light describes what radiation measurement device?

A

TLDs

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23
Q

Why is LiF used? (2)

A

the atomic number is close to tissue equivalent
thermoluminescence

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24
Q

For TLDs light released is _________ to the radiation dose

A

proportional

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25
Q

How are residual affects from exposure and removed from TLDs?

A

Annealing

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26
Q

heating plus slow cooling explains the process of __? What is it for?

A

Annealing
Remove effects of previous exp

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27
Q

Which dosimeter has advantages of reusable, good tissue equivalence and small?

A

TLD

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28
Q

TLD advantages (3)

A

reusable
tissue equivalence
small

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29
Q

TLD disadvantages (3)

A

No immediate readout
low spatial resolution
fragile

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30
Q

Which dosimeter uses a P and N type junctions

A

diode

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31
Q

What dosimeter is similar to how an ion chamber works by inducing a current, but it uses a solid instead of air?

A

diode

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32
Q

where the P region and N region meet is called?

A

depletion region

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33
Q

Advantages to silicon diodes (4)

A
  • immediate readout
  • small
  • sensitive
  • durable
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34
Q

Which dosimeter has the following advantages?
immediate readout
small
sensitive
durable

A

diode

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35
Q

Which dosimeter is used for QA (depth dose and profile)

A

diode

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36
Q

Disadvantages of diodes: (3)

A

energy dependence in photons beams
directional dependence
sensitive to heat and radiation damage

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37
Q

A film that is not based on silver halide but a radiosensitive monomer

A

Radiochromic film

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38
Q

Advantages of MOSFETs:

A

immediate read-out
reusable
small and lightweight

39
Q

MOSFETs stands for

A

Metal oxide semiconductor-field effect transistor

40
Q

What would be used for QA and light radiation field.

A

Radiochromic film

41
Q

What is the type of filtration? Filtration that would remove all low energy x-rays

A

Ideal filtration

42
Q

What is being measured under “good geometry”?

A

HVL

43
Q

Thoreaus filter order (4 things)

A

tin, copper, aluminum, patient

44
Q

Filter that must be arranged in proper order of highest atomic # closest to the target

A

Thoreaus filter

45
Q

Collisions between photons and charge particles results and electrons which dissipate energy vehicle collisions leading to ionization and excitation

A

Coll KERMA

46
Q

Energy transfer via radiative photons (bremsstrahlung )

A

Radiative KERMA

47
Q

energy fluence formula

A

(#Ofphotons x energy of photons) + (# Of photons x energy of photons)

48
Q

What are limits for exposure (R): (3)

A

Only valid for photons( xray & gamma ray)
3 mev limit
Only for air ionization

49
Q

What is CPE used to measure?

A

Exposure in ion chamber

50
Q

Limits to exp: (3)

A

Only valid for photons (xray & gamma ray)
3 mev limit
Only for air ionization

51
Q

Correction factors for FAC: (3)

A

Air density changes
Ion recombination
Air attenuation of photons

52
Q

Stem effect varies w/?

A

energy

53
Q

What chamber has a collection volume .6cm^3

A

Farmer

54
Q

What chamber is well guarded and has 3 electrodes

A

Farmer

55
Q

What are the 3 electrodes of a farmer chamber

A

Central electrode - collector
Thimblewall - tissue equivalent ( pure graphite)
Gaurd electrode

56
Q

Which of the following would be a primary standard for ion chamber

A

FAC

57
Q

What uses temperature rise as a dosimeter

A

Calorimetry

58
Q

TG 21 was based what machine

A

Co

59
Q

Which TG is based on exposure to air kerma

A

TG 21

60
Q

Which TG is based on absorbed dose in water

A

TG51

61
Q

If you put collimator or shield closer to the skin it does what? What affect does it have on penumbra?

A

Increases SDD
Decreases penumbra

62
Q

Fricke dosimeter uses what to determin change

A

Spectrophotometer

63
Q

What measurememnt device is this? Electrons excited, become trapped in conduction band, when heated they are released and recombin in valence band, and release light.

A

TLD

64
Q

Which dosimeter has advantages of reuable, good tissue equivalence and small?

A

TLD

65
Q

What are limitations to TLD? (3)

A

No immediate readout, low spatial resolution and fragile

66
Q

Which dosimeter has immediate readout

A

Silicon Diodes

67
Q

Adv diodes (4)

A

immediate readout
small
sensitive
durable

68
Q

What measurement device is energy dependent in photons?

A

diode

69
Q

What is insensitive to radiation and requires 10-50Gy

A

Radiochromic film

70
Q

MOSFETs stands for

A

Metal oxide semiconductor-field effect transistor

71
Q

Why are new couches all carbon fiber?

A

Low Z material and therefore easier to treat thru

72
Q

Magnetron or kylstron:
Used for high energy and more expensive

A

Klystron

73
Q

Magnetron or klystron: require low energy microwave source (RF driver)

A

Klystron

74
Q

Magnetron or klystron: electrons get exposed to a magnetic field which converts them into microwaves

A

magnetron

75
Q

What type of gas is in the accelerator tube

A

SF6

76
Q

What type of target is in a linac?

A

transmisssion

77
Q

What type of target is in an xray tube

A

Reflection target/rotating anode

78
Q

What are the conditions at which a MU is defined

A

Amount of time to deliver 1 cGy at 10x10 cm FS at DMax at 100cm awa

79
Q

Why are secondary collimators move divergently with the beam?

A

transmission penumbra

80
Q

What penumbra is due to the finite dimension of the source/ focal spot

A

geometric

81
Q

Which penumbra is the spread of dose distriubtion near field borders

A

physical

82
Q

Does ion chamber go before the flattening filter?

A

no

83
Q

Which of the following linacs uses a Physical source?

A

Co

84
Q

Average energy of cobalt machine?

A

1.25 MeV

85
Q

How many modes of decay does cobalt 60 have & what are they?

A

2 modes: 1.17 mev / 1.33 mev

86
Q

Cobalt 60 is housed in what?

A

Stainless steel capsule

87
Q

What is the size of cobalt source?

A

1-2 cm in diameter

88
Q

Cobalt loses __% activity per month?

A

1

89
Q

Betatron is also called

A

donut

90
Q

Xray output is sensitive to the ___ ___.

A

filament current

91
Q

Xray output increase____________ with tube current, and________of the to tube voltage

A

Proportionally / squared

92
Q

The higher the energy of the electron bombarding the target the more__________ the direction of the xray emission

A

forwardss

93
Q

What are the 3 primary dosimeters?

A

FAC
Calorimetry
Fricke

94
Q
A

Dosimetry Physics 1 (7 decks)

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