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Science and Technology 1 > X-ray Generation > Flashcards

X-ray Generation Flashcards

(108 cards)

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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
What does the shape of the focussing cup in the x-ray tube help to do?
It helps to converge (connect) the electrons onto the focal point
26
What would happen if the focussing cup in the x-ray tube didn’t have its particular shape?
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
27
What is the charge of electron?
Negative
28
What does increasing the mean photon energy do?
It causes the release of fewer photons of lower energy
29
What does an increased x-ray output do?
It allows the x-ray to stay closer to the maximum for longer
30
What does a shorter exposure of x-rays do?
Since the output is higher, it allows the exposure to be shorter in time but still getting the same output
31
What does a lower patient dose do?
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
32
Between the rectified current and the 3 phase supply, which has the higher average energy?
3 phase supply
33
What do transformers doing the x-ray tube?
They provide the high voltages that are used in x-ray production
34
How many volts are the mains electricity at home?
230 volts
35
How many volts is a chest x-ray exposure?
125 000 volts
36
What does a vacuum in the x-ray tube do?
It prevents electrons from losing energy
37
Why do we need a vacuum in the x-ray tube? (5)
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
38
What does the anode look like? (3)
It’s a disk It’s at a slight angle It rotates
39
Why is the anode a rotating disk?
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
40
What is the equation for heat?
Heat (J) = w x KvP x mAs
41
What is heat measured in?
Joules (J)
42
What does w stand for in the heat equation?
It’s the waveform (shape of the wave) of the voltage through the x-ray tube
43
The more uniform (consistent) the waveform… (Heat production)
The lower the heat production
44
What does the heat capacity show?
It shows how much the temperature rises with heat input
45
What is the equation for temperature rise?
Energy applied / heat capacity
46
Is a higher or lower heat capacity desirable for anodes?
Higher
47
Why is a higher heat capacity desirable for anodes?
So the anode doesn’t become too hot and melt
48
What does increasing the heat removed from the system increase?
Heat capacity
49
How is heat capacity represented?
By tube rating charts
50
What 3 factors allow for a safer heat capacity?
Lower kV Lower mA Shorter time
51
What is the advantage of the anode rotating?
It allows the parts of the anode that have been hit by electrons time to cool down, so they don’t melt
52
What are the features of the target material of the anode? (5)
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
What does the target material of the anode man?
It means what the anode is made of
54
Why is it an advantage of the target material of the anode that it has a high atomic number?
It allows for more electrons to interact with the target material
55
Why is it an advantage of the target material of the anode that is has a high melting point?
It won’t melt
56
Why is it an advantage of the target material of the anode that it has a high thermal conductivity?
It dissipates heat (takes away heat well)
57
Why is it an advantage of the target material of the anode that it has a low vapour pressure at working temperature?
It prevents sublimation, which can damage the tube
58
What are the 2 different types of anodes?
Stationary Rotating
59
Where are stationary anodes mainly found? (2)
In dental radiology and Radiotherapy systems
60
How do stationary anodes work?
The electron beam constantly hits one small area
61
Why are stationary anodes used in dental radiology?
Because the electron beam is going through thinner/less material
62
What charge does a rotating anode disk have?
Positive
63
Why does a rotating anode disk have a positive charge?
To attract electrons (which have a negative charge) towards it
64
Why does a rotating anode disk rotate?
To dissipate (release) heat
65
How much does the rotating anode disk rotate?
50 Hz
66
What is the temperature of the rotating anode disk?
2000 degrees
67
Is a larger rotating anode disk better or worse for heat transfer?
Better
68
Why is the rotating anode disk’s target angled? (2)
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
What is the focal point in the x-ray tube?
The area of the target that’s impacted by the electrons where x-rays are produced
70
What does the target being at an angle increase?
The effective focal point
71
What does a smaller area of the focal point cause?
A more precise x-ray beam, but it means there’s an increase in heat
72
What is the angle of the anode?
Between 7-20 degrees
73
What does the angle of the anode affect? (2)
Effective focal point size Heel effect
74
What does a larger anode angle increase?
Effective focal point size
75
Why might different examinations require different anode angles?
Because the angle depends on the power needed for the heat and resolution
76
What is the target stem?
A molybdenum disk with a thin tungsten target
77
Is a molybdenum stem a good or poor heat conductor?
Poor heat conductor (it conducts little heat)
78
What does the target stem (molybdenum stem) include? (2)
Silver lubricated bearings Blackened rotor
79
Why does the molybdenum stem have a blackened rotor?
For heat transfer
80
What is the disk also known as?
The anode
81
Why is it important to minimize heat conduction to the bearings in the molybdenum stem?
To prevent the bearings from melting and causing damage
82
What is the x-ray tube housed in? Why?
Oil To dissipate heat
83
What is a problem with the x-ray tube being housed in oil?
It can leak
84
What does the anode cooling chart show?
It shows how long it takes for the anode to cool from maximum heat
85
Why is the anode cooling charge important?
Because it’s used to prevent anode damage between exposures
86
What could a worn anode lead to? (2)
Inconsistent output Inconsistent image quality
87
What can the casing on the x-ray tube be made of? (2)
Aluminium or Steel
88
What is the casing of the x-ray tube an insulator for? (2)
Electrical insulator Heat insulator
89
Why is the casing of the x-ray tube important? (2)
It shields radiation from going in the wrong direction It protects the components of the x-ray tube
90
What is an issue with the casing of the x-ray tube?
It can cause head injuries
91
Are all the energies of the x-ray beam useful?
No
92
What does filtration do?
It cuts out some of the useless energies
93
Why are low energy photons bad?
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
What does filtration do to the low energy photons?
The low energy photons are absorbed by the filters
95
What does the anode heel effect say?
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
What are the 2 types of collimation?
Cylindrical collimation Rectangular collimation
97
Which type of collimation is used now?
Rectangular collimation
98
Which type of collimation isn’t used anymore?
Cylindrical collimation
99
What does collimation reduce?
It reduces the risk of radiation
100
Why is cylindrical collimation not used anymore?
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
What do collimators do?
They restrict the span of the x-ray beam. So they block part of the beam- they don’t focus it
102
What are collimators typically made of?
Lead shutters
103
What does the light beam diaphragm do?
It allows us to see where the x-ray beam is being directed and how it’s collimated
104
What does decreasing the area (amount) of the x-ray beams being exposed result in?
A higher quality image
105
Why is the light beam diaphragm good? (2)
It reduces the amount of scattered radiation It reduces the dose to the patient
106
What is an issue with the light beam diaphragm?
It affects post processing
107
How many lines of collimation does a good x-ray have?
4 lines of collimation
108
How many lines of collimation does a good x-ray have?
4 lines of collimation

Science and Technology 1 (17 decks)

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