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Physics > Ch 6 The X-ray Tube > Flashcards

Ch 6 The X-ray Tube Flashcards

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1
Q

the anode is the _____ end, the cathode is the ____ end

A

positive, negative

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2
Q

x-rays travel from _____ to ______

A

cathode to anode

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3
Q

where is heat the biggest problem?

A

at the anode

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4
Q

the focal spot is the _____ source, they get there through______

A

electron, boiling off of the filament

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5
Q

there are ___ filaments

A

2, a small focal spot and a big focal spot

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6
Q

filaments are usually made out of:

A

thoriated tungsten

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7
Q

what are the rmp rates for rotating anodes?

A

3,400 rmp & 10,000 rpm

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8
Q

the _______ is on the anode side

A

induction motor

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9
Q

the induction motor is made up of 2 parts:

A

rotor and stators

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10
Q

the rotor:

A

rotates the anode, it is inside the glass tube proper

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11
Q

the stator:

A

is made of electromagnets, provides electric and magnetic fields and electron flow, creates the force that creates the rotation, is outside of the glass tube proper

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12
Q

the target is found on the _____ and is made of _____

A

anode, tungsten

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13
Q

the rotor is on the ______ side and is made of _____

A

anode, tungsten

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14
Q

the actual focal spot is:

A

where the electrons actually hit, where the heat is, is bigger to dissipate heat better

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15
Q

the effective focal spot is:

A

what hits the IR, is smaller, provides detail

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16
Q

cathode end has __% of the beam and it used on ____ parts, generally placed at the ____

A

> 100% beam, thicker parts, placed at the head end

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17
Q

anode end has __% of the beam and is used on _____ parts, generally places at the ____

A

<100% beam, thin parts, placed at the feet end

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18
Q

the window is:

A

made of pyrex glass, is thin, what the photons go through

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19
Q

extra-focal x-rays are:

A

radiation produced anywhere else besides the anode target area of focal spot

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20
Q

the primary parts of the x-ray tube are:

A

cathode (-) and anode (+)

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21
Q

any electric tube with 2 electrodes is a:

A

diode

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22
Q

the external structure of the x-ray includes:

A

the support structure, protective housing, and a glass or metal enclosure

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23
Q

when x-rays are produced they are emitted:

A

isotropically (with equal density in all directions)

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24
Q

x-rays emitted through the window are:

A

the useful beam

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25
Q

leakage radiation:

A

x-rays that escape through the protective housing, they contribute nothing to diagnostics

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26
Q

protective housing reduces:

A

the level of leakage radiation to less than 1 mGya/hr at 1m OR 100mR/hr at 1m from the source

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27
Q

*protective housing guards against:

A

excessive radiation exposure and electric shock

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28
Q

protective housing around some x-ray tubes contains oil that:

A

serves as an insulator against electric shock and as a thermal cushion to dissipate heat

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29
Q

glass enclosures are made of ____ and are able to ____

A

pyrex glass, withstand tremendous heat

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30
Q

the enclosure maintains:

A

a vacuum inside the tube

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31
Q

the modern x-ray tube is called ____

A

Coolidge tube or vacuum tube

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32
Q

metal enclosures maintain:

A

a constant electric potential b/w the electrons of the tube current and the enclosure, they have a longer life and are less likely to fail

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33
Q

*x-ray tubes are designed with ___ or ___ enclosures

A

glass or metal

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34
Q

the x-ray tube window is where ______, it allows____

A

the useful beam of x-rays is emitted, it allows maximum emission of x-rays with minimum absorption

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35
Q

*the primary parts of the cathode are:

A

the filament and the focusing cup

36
Q

a filament is a:

A

coil of wire

37
Q

the filament emits:

A

electrons when it is heated

38
Q

when the current through the filament is high enough the:

A

outer shell electrons get boiled off and ejected from the filament, aka thermionic emission

39
Q

filaments are usually made out of:

A

thoriated tungsten

40
Q

*tungsten vaporization causes:

A

deposits on the inside of the glass enclosure, it is the most common cause of tube failure and can cause arcing

41
Q

the filament is embedded in:

A

a metal shroud called the focusing cup

42
Q

the focusing cup is ___ charged so that is:

A

negatively, so that is electrostatically confines that electron beam to a small area of the anode

43
Q

most rotating anodes have __ filaments

A

2, a large and a small focal spot

44
Q

grid-controlled tubes are designed to:

A

turn on and off rapidly

45
Q

*x-ray tube current is adjusted by:

A

controlling the filament current

46
Q

because electrons carry negative charges:

A

they repel one another and tend to form a cloud around the filament

47
Q

this cloud of electrons is called _____ and it:

A

space charge, it makes it difficult for other electrons to be emitted by the filament b/c of electrostatic repulsion (electrons are stuck at the cathode end b/c they are attracted to the focusing cup)

48
Q

*thermionic emission at ___ kVp and ___ mA can be space charge limited

A

low kVp and high mA

49
Q

saturation current:

A

at any given filament current, the x-ray current rises with increasing voltage to a maximum value, a further increase in kVp doesn’t result in a higher mA because all available electrons have been used

50
Q

filament current is measured in ____

tube current is measured n ____

A

A

mA (technique factor)

51
Q

small FS is used when, measurement:

A

better spatial resolution is required, 0.1-1mm

52
Q

large FS is used when, measurement:

A

large body parts or when techniques that produce high heat are used, 0.3-2mm

53
Q

stationary anodes are used in:

A

dental, portables, and special units where high tube current and power are NOT required

54
Q

*the anode does 3 things:

A

conducts electricity, radiates heat, and contains the target

55
Q

the anode receives electrons emitted by the cathode and conducts them through the tube and back to the _____

A

high-voltage generator

56
Q

the anode is a ______, and also provides ______, and must be a good ______

A

electrical conductor, mechanical support for the target, thermal dissipator

57
Q

more than __% of _____ turns into heat

A

99% of electron kinetic energy

58
Q

most common anode materials:

A

copper, molybdenum, and graphite

59
Q

in STATIONARY ANODES the target is:

A

tungsten alloy embedded in a copper anode

60
Q

in ROTATING ANODES the target is:

A

a rotating tungsten disc

61
Q

tungsten is used for the target for 3 reasons:

A
  • high atomic # (74), high energy x-rays
  • thermal conductivity, efficient metal for dissipating heat
  • high melting point, 3,400C can withstand high tube current
62
Q

the rotating anode provides ____ times more _____

A

500x more area to interact with electron beam

63
Q

*____ tube current and _____ exposure times are possible with the rotating anode

A

high tube current and shorter exposure times

64
Q

*the focal spot size is the:

A

actual x-ray source

65
Q

*line-focusing principle:

A

by angling the target, the effective area is much smaller than the actual area

66
Q

target angles can vary from ______

A

5-20 degrees

67
Q

the intensity of the x-rays emitted on the heel end of the target are:

A

reduced because they have a longer path and increased absorption

68
Q

*the smaller the angle, the ___ the heel effect

A

larger

69
Q

at the CR the beam intensity is __%

A

100%

70
Q

at the cathode side the beam intensity:

A

can be up to 120%

71
Q

at the anode side the beam intensity:

A

can be as low as 75%

72
Q

positioning the cathode end over the _____ anatomy provides _____

A

thickest anatomy provides more uniform exposure (density)

73
Q

*heel effect results in ___ effective FS and ___ radiation intensity on the anode side of the beam

A

smaller effective FS and less radiation intensity

74
Q

radiation:

A

transfer of heat by emission of infrared radiation

75
Q

conduction:

A

transfer of energy from one area of an object to another

76
Q

convection:

A

transfer of heat by the movement of a heated substance from one place to another

77
Q

*excessive heat results in:

A

reduced tube life

78
Q

*maximum techniques should:

A

never be applied to a cold anode

79
Q

*most frequent cause of abrupt tube failure is:

A

electron arcing from the filament to the enclosure because of tungsten vaporization

80
Q

radiographic rating chart tells you:

A

which techniques are safe to use and which are not safe to use for x-ray tube operation

81
Q

in the rating chart the x & y axis are:

A

kVp & time

82
Q

the curve represents:

A

tube currents in mA

83
Q

any combo of kVp & time that is below the mA curve is:

A

safe to use

84
Q

anode cooling chart tells you:

A

the thermal capacity of the anode (maximum heat capacity) and determines the length of time required for complete cooling

85
Q

single phase HU=

A

kVp x mA x s = 0.7J

86
Q

3 phase/high frequency HU=

A

kVp x mA x s = 1J

87
Q

complete cooling of the housing requires ___ hours

A

1-2 hours

Physics (13 decks)

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