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Science and Technology 1 > X-ray Generation > Flashcards

X-ray Generation Flashcards

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1
Q

What is radon gas also known as?

A

Natural gas

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2
Q

What is the average dose of radiation to the population from natural gas?

A

2.6 Sv p.a

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3
Q

Why does electromagnetic radiation having different properties depend on?

A

The wavelength of the waves that form the radiation

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4
Q

Why are x-rays and gamma rays ionising radiation?

A

Because they have enough energy to knock electrons off atoms and cause damage

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5
Q

Who discovered x-rays?

A

Wilhelm Rotegan

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6
Q

How did Wilhelm Rotegan discover x-rays?
(4)

A

He covered a crooked tube with black cardboard

He darkened the room and powered on the tube

He saw a faint glow on a barium planticocyanide screen 8 feet away

He then realised that an invisible ray was passing through the cardboard

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7
Q

When x-ray were first used, what was the radiation dose like?

A

Very high- much higher than now

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8
Q

What are the differences between x-rays are gamma rays?
(2)

A

X-rays can be turned off
Gamma rays can’t be turned off

X-rays are produced by unstable atoms decaying and releasing energy
Gamma rays are produced by electromagnets

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9
Q

What are bearings in x-ray tubes made of?

A

Silver

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10
Q

What does HT cable in x-ray tubes stand for?

A

High tension cable

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11
Q

How do x-ray tubes work?
(11)

A

Cathode filament heated
Gets hot
Atoms gets lots of energy
Atoms move faster
Electrons released
Electrons accelerated by tube potential
Electrons crash into anode
Electrons lose kinetic energy and stop moving
Heat produced
Radiation produced
Heat must be dissipated (or tubes would melt(

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12
Q

What is produced when electrons crash into the anode?
(2)

A

Heat
Radiation

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13
Q

What 2 types of radiation are produced when the electrons in the x-ray tube crash into the anode?

A

Bremstrahhlung radiation
Characteristic radiation

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14
Q

What happens when the 2 types of radiation have ben produced in the x-ray tube?
(3)

A

The radiation is produced in all directions
The radiation needs to be collimated
The radiation is then detected

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15
Q

Which end of the x-ray tube is the cathode?

A

The negative end

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16
Q

What does the filament in the x-ray tube do?

A

It’s the source of the electrons

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17
Q

What is the filament in the x-ray tube made of?

A

A coil made of Tungsten

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18
Q

What does the filament in the x-ray tube contain?
What does that do?

A

It contains 1% thorium

It increases the release of electrons via thermionic emission

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19
Q

What is thermionic emission?

A

The liberation (release) of electrons from an electrode by virtue of its temperature

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20
Q

Why is the x-ray filament a coil?

A

Because it’s a controlled source of electrons that are used to produce x-ray beams

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21
Q

What is the focussing cup in the x-ray tube?

A

It’s a negatively charged shallow depression that’s found on the surface of the cathode

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22
Q

What does the focussing cup in the x-ray tube do?

A

It concentrates the electron beam towards the focal spot of the anode

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23
Q

What is the focussing cup in the x-ray tube mainly made of?

A

Nickel

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24
Q

What does the negative charge of the focussing cup in the x-ray tube help to do?

A

It helps to accelerate the electrons towards the anode

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25
Q

What does the shape of the focussing cup in the x-ray tube help to do?

A

It helps to converge (connect) the electrons onto the focal point

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26
Q

What would happen if the focussing cup in the x-ray tube didn’t have its particular shape?

A

The repulsion between the negatively charged electrons would cause the electrons to spread out as they reach the anode, causing only some of the electrons to reach the anode

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27
Q

What is the charge of electron?

A

Negative

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28
Q

What does increasing the mean photon energy do?

A

It causes the release of fewer photons of lower energy

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29
Q

What does an increased x-ray output do?

A

It allows the x-ray to stay closer to the maximum for longer

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30
Q

What does a shorter exposure of x-rays do?

A

Since the output is higher, it allows the exposure to be shorter in time but still getting the same output

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31
Q

What does a lower patient dose do?

A

It allows for an increased mean energy, so fewer low energy photons contribute to the patient’s dose, but they don’t contribute to the final image

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32
Q

Between the rectified current and the 3 phase supply, which has the higher average energy?

A

3 phase supply

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33
Q

What do transformers doing the x-ray tube?

A

They provide the high voltages that are used in x-ray production

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34
Q

How many volts are the mains electricity at home?

A

230 volts

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35
Q

How many volts is a chest x-ray exposure?

A

125 000 volts

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36
Q

What does a vacuum in the x-ray tube do?

A

It prevents electrons from losing energy

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37
Q

Why do we need a vacuum in the x-ray tube?
(5)

A

There’s a high potential pulling the electron to the anode

But they’re particles in the way, and the electrons will end up interacting with them

This would cause the electrons to lose energy

The electrons would get scattered

So we need to remove all the particles in the way

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38
Q

What does the anode look like?
(3)

A

It’s a disk
It’s at a slight angle
It rotates

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39
Q

Why is the anode a rotating disk?

A

It allows the spreading of electrons, so more electrons can hit more of the disk,which allows for the heat to be distributed over a larger area

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40
Q

What is the equation for heat?

A

Heat (J) = w x KvP x mAs

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41
Q

What is heat measured in?

A

Joules (J)

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42
Q

What does w stand for in the heat equation?

A

It’s the waveform (shape of the wave) of the voltage through the x-ray tube

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43
Q

The more uniform (consistent) the waveform…
(Heat production)

A

The lower the heat production

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44
Q

What does the heat capacity show?

A

It shows how much the temperature rises with heat input

45
Q

What is the equation for temperature rise?

A

Energy applied / heat capacity

46
Q

Is a higher or lower heat capacity desirable for anodes?

A

Higher

47
Q

Why is a higher heat capacity desirable for anodes?

A

So the anode doesn’t become too hot and melt

48
Q

What does increasing the heat removed from the system increase?

A

Heat capacity

49
Q

How is heat capacity represented?

A

By tube rating charts

50
Q

What 3 factors allow for a safer heat capacity?

A

Lower kV
Lower mA
Shorter time

51
Q

What is the advantage of the anode rotating?

A

It allows the parts of the anode that have been hit by electrons time to cool down, so they don’t melt

52
Q

What are the features of the target material of the anode?
(5)

A

It’s usually tungsten
It has a high atomic number
It has a high melting point (doesn’t melt)
It has a high thermal conductivity
It has a low vapour pressure at working temperature

53
Q

What does the target material of the anode man?

A

It means what the anode is made of

54
Q

Why is it an advantage of the target material of the anode that it has a high atomic number?

A

It allows for more electrons to interact with the target material

55
Q

Why is it an advantage of the target material of the anode that is has a high melting point?

A

It won’t melt

56
Q

Why is it an advantage of the target material of the anode that it has a high thermal conductivity?

A

It dissipates heat (takes away heat well)

57
Q

Why is it an advantage of the target material of the anode that it has a low vapour pressure at working temperature?

A

It prevents sublimation, which can damage the tube

58
Q

What are the 2 different types of anodes?

A

Stationary
Rotating

59
Q

Where are stationary anodes mainly found?
(2)

A

In dental radiology and
Radiotherapy systems

60
Q

How do stationary anodes work?

A

The electron beam constantly hits one small area

61
Q

Why are stationary anodes used in dental radiology?

A

Because the electron beam is going through thinner/less material

62
Q

What charge does a rotating anode disk have?

A

Positive

63
Q

Why does a rotating anode disk have a positive charge?

A

To attract electrons (which have a negative charge) towards it

64
Q

Why does a rotating anode disk rotate?

A

To dissipate (release) heat

65
Q

How much does the rotating anode disk rotate?

A

50 Hz

66
Q

What is the temperature of the rotating anode disk?

A

2000 degrees

67
Q

Is a larger rotating anode disk better or worse for heat transfer?

A

Better

68
Q

Why is the rotating anode disk’s target angled?
(2)

A

To increase the area of heat distribution, so we can get the biggest surface area for the heat being dissipated (released)

So it can compromise between image and heat dissipation (release)

69
Q

What is the focal point in the x-ray tube?

A

The area of the target that’s impacted by the electrons where x-rays are produced

70
Q

What does the target being at an angle increase?

A

The effective focal point

71
Q

What does a smaller area of the focal point cause?

A

A more precise x-ray beam, but it means there’s an increase in heat

72
Q

What is the angle of the anode?

A

Between 7-20 degrees

73
Q

What does the angle of the anode affect?
(2)

A

Effective focal point size

Heel effect

74
Q

What does a larger anode angle increase?

A

Effective focal point size

75
Q

Why might different examinations require different anode angles?

A

Because the angle depends on the power needed for the heat and resolution

76
Q

What is the target stem?

A

A molybdenum disk with a thin tungsten target

77
Q

Is a molybdenum stem a good or poor heat conductor?

A

Poor heat conductor (it conducts little heat)

78
Q

What does the target stem (molybdenum stem) include?
(2)

A

Silver lubricated bearings

Blackened rotor

79
Q

Why does the molybdenum stem have a blackened rotor?

A

For heat transfer

80
Q

What is the disk also known as?

A

The anode

81
Q

Why is it important to minimize heat conduction to the bearings in the molybdenum stem?

A

To prevent the bearings from melting and causing damage

82
Q

What is the x-ray tube housed in?
Why?

A

Oil

To dissipate heat

83
Q

What is a problem with the x-ray tube being housed in oil?

A

It can leak

84
Q

What does the anode cooling chart show?

A

It shows how long it takes for the anode to cool from maximum heat

85
Q

Why is the anode cooling charge important?

A

Because it’s used to prevent anode damage between exposures

86
Q

What could a worn anode lead to?
(2)

A

Inconsistent output

Inconsistent image quality

87
Q

What can the casing on the x-ray tube be made of?
(2)

A

Aluminium or
Steel

88
Q

What is the casing of the x-ray tube an insulator for?
(2)

A

Electrical insulator
Heat insulator

89
Q

Why is the casing of the x-ray tube important?
(2)

A

It shields radiation from going in the wrong direction

It protects the components of the x-ray tube

90
Q

What is an issue with the casing of the x-ray tube?

A

It can cause head injuries

91
Q

Are all the energies of the x-ray beam useful?

A

No

92
Q

What does filtration do?

A

It cuts out some of the useless energies

93
Q

Why are low energy photons bad?

A

They can contribute towards the dose received by the patients but not to the image, because those photons would be absorbed by the patient

94
Q

What does filtration do to the low energy photons?

A

The low energy photons are absorbed by the filters

95
Q

What does the anode heel effect say?

A

There’s a higher intensity of x-rays at the cathode, so larger materials are put at the cathode. Therefore, more x-rays are absorbed at the anode. This shows that the x-ray beam isn’t the same across the whole area

96
Q

What are the 2 types of collimation?

A

Cylindrical collimation

Rectangular collimation

97
Q

Which type of collimation is used now?

A

Rectangular collimation

98
Q

Which type of collimation isn’t used anymore?

A

Cylindrical collimation

99
Q

What does collimation reduce?

A

It reduces the risk of radiation

100
Q

Why is cylindrical collimation not used anymore?

A

The radiation around the edge isn’t recorded by the detector, but the patients are exposed to that radiation, meaning that they’re exposed to more radiation

101
Q

What do collimators do?

A

They restrict the span of the x-ray beam. So they block part of the beam- they don’t focus it

102
Q

What are collimators typically made of?

A

Lead shutters

103
Q

What does the light beam diaphragm do?

A

It allows us to see where the x-ray beam is being directed and how it’s collimated

104
Q

What does decreasing the area (amount) of the x-ray beams being exposed result in?

A

A higher quality image

105
Q

Why is the light beam diaphragm good?
(2)

A

It reduces the amount of scattered radiation

It reduces the dose to the patient

106
Q

What is an issue with the light beam diaphragm?

A

It affects post processing

107
Q

How many lines of collimation does a good x-ray have?

A

4 lines of collimation

108
Q

How many lines of collimation does a good x-ray have?

A

4 lines of collimation

Science and Technology 1 (17 decks)

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