The X-Ray Tube (Chapter 5) Flashcards
1
Q
What are the internal X-ray tube components?
A
Cathode and Anode
2
Q
What are the external X-ray tube components?
A
- Support structure
- Protective housing
- Glass or metal enclosure
3
Q
X-ray production is only possible under these conditions:
A
- Source of electrons
- Appropriate target material
- High voltage
- Vacuum
4
Q
Cathode side is _____ (negative, positive)
A
Negative
5
Q
What is the function of a cathode?
A
- To produce thermionic cloud ⭐️⭐️⭐️⭐️
- Conduct high voltage to gap between cathode and anode
- Focus electron stream towards the anode
6
Q
Cathode assembly consists of: (list 3)
A
- Filaments
- Focusing cup
- Associated wiring
7
Q
What is a filament?
A
Small coil of thoriated tungsten wire
8
Q
Why is tungsten important?
A
- High melting point
- Difficult to vaporize
9
Q
What is the function of a filament?
A
resistance to the flow of electrons
so that the heat produced will cause thermionic emission
10
Q
What is the space charge effect?
A
As more and more electrons are produced at the filament, their negative charges don’t allow any additional electrons
11
Q
What does the focusing cup do?
A
Narrows the thermionic cloud
12
Q
What is the focusing cup?
A
Small cup with wire
13
Q
Focusing cup pulsed between negative and positive charge to remove electrons from use is called ___?
A
Grid -pulsed or Grid controlled
14
Q
What are the functions of the anode? (List 3)
A
1.Target surface for electrons
2. Conducts high voltage from the cathode back into the X-ray generator
3. Primary thermal conductor
15
Q
What does the Anode Assembly consist of?
A
- Anode (target)
- Stator
- Rotor
16
Q
List 2 types of Anode (Targets)
A
- Stationary
- Rotating
17
Q
Function of a rotating anode?
A
- Source of X-ray photons
- Primary thermal conductor
18
Q
Common rotating anodes revolve at ____ ?
A
3,200 - 3,600 rpm
19
Q
High speed anodes revolve at _____?
A
10,000 - 12,000 rpm
20
Q
Tungsten is the metal of choice for 3 reasons
A
- High atomic number (74)
- High melting point
- Heat-conducting ability
21
Q
What is tungsten’s atomic number?
A
74
22
Q
What is pitting?
A
Normal use of a rotating anode will eventually vaporize the target track material
(Reduces the efficiency of the tube)
23
Q
What is cracking?
A
Failure to warm the tube up to range of operation before use can crack the anode
24
Q
What is the focal track?
A
The circular path that will be impacted by the electron stream and where the X-ray photons are produced
25
What is the actual focal spot?
The physical area of the focal track that is impacted by
26
What is the effective focal spot?
Area of the focal spot that is projected out of the tube toward the object being radiographed
27
The effective focal spot is controlled by:
1. The actual focal spot
2. Size of filament
3. Anode target angle
28
What is the Anode Heel Effect?
Because of the geometry of an angled anode target, the radiation intensity is greater on the cathode side.
29
The anode heel effect is most noticeable at: (list 3)
1. Short SID
2. Large image receptor
3. Small focal spot
30
The only part of the cathode or anode assemblies that is located outside the vacuum or the envelope
Stator
31
True or False
If the stator fails, the rotor will cease to turn the anode, resulting in the immediate melting of a spot on the target
True
32
Where is the Rotor located?
Located inside the stator and inside the envelope
33
The rotor revolves at _____ rpm
3,200 - 3,600
34
Rotor failures happen when?
There is high speed harmonic damage
(Between 5,000 - 7,000 rpm the harmonics produced by the rotating cuff are at a frequency capable of shattering the glass envelope)
35
What is the gyroscopic effect?
Basically like a spin top the rotor keeps it stable but then eventually something happens and it wobbles and falls
When the anode rotates quickly in different positions. Gyroscopic effect happens cuz it gets damaged
36
The envelope is made up of what kind of glass?
Heat resistant Pyrex glass
37
The primary function of the envelope ?
To maintain the vacuum between the cathode and anode
38
The protective housing controls: (list 3)
1. Leakage and scatter radiation
2. Isolates the high voltages
3. Provides a mean to cool the tube
39
The protective housing is made up of :
Made of steel and lined with lead
40
When x-ray photons are produced at the anode, they are emitted _____ (in all directions)
Isotropically
41
The primary beam consists of:
Photons emitted through the window
42
Leakage radiation must not exceed _____ mR/hr at ____ meter
100 mR/hr at 1 meter
43
Off focus or extra focal radiation is:
Photons that were not produced at the focal spot
44
What is ghosting?
Ghosting in an X-ray tube is the appearance of faint, transparent images from previous X-ray exposures on a new X-ray image, caused by residual radiation.
45
High voltage electrons striking the focal spot produce ____ electrons or photons
Scattered
46
List 3 cathode filament materials:
1. Tungsten
2. Rhenium
3. Molybdenum
47
Filament materials are chosen primarily for their___?
High melting points & difficult to vaporize
48
List 3 things that would affect the production of a thermionic cloud
1. Filament diameter
2. Filament length
3. Filament temperature
49
A filament may break due to ____
Vaporization
50
Driving the thermionic cloud from the cathode to the anode requires ____
High - Voltage
51
The cathode focusing cup has a _____ charge
Negative
52
As more and more electrons build up in the area of the filament, their negative charges oppose the emission of additional electrons. This phenomenon is known as ______
Space charge effect
53
X-ray photon production occurs at the
Anode
54
Tungsten is the material of choice for the source of X-ray photons primarily because of its
High atomic number
Heat conductivity ability
High melting point
55
Pitting of the anode commonly occurs ____
With extended use
56
Melting of the anode commonly occurs when …
When the stator fails and the rotor ceases to turn
57
Cracking of the anode typically occurs when …
When a cold anode is hit with a high kVp exposure
58
The exact point on the anode where the x-ray beam comes out is the ____
Effective focal spot
59
The physical area of a rotating anode focal track, affected by the cathode electron beam, is the ____
Actual focal spot
60
The area of the focal spot that is projected out of the tube toward the object being radiographed is the
Effective focal spot
61
The actual focal spot is controlled by the
Length of the filament
62
The most common diagnostic radiography x-ray tube target angle is ___ degrees
12
63
As the actual focal spot size increases, the effective focal spot size _____
(Decreases, increases, doesn’t change)
Increases (they are directly related)
64
As the angle of the anode increases and the incident electron beam size remains the same, the effective focal spot size ____
(Decreases, increases, doesn’t change)
Increases
65
The use of the line-principle causes a problem knows as the _____ effect
Anode heel effect
66
The only portion of the anode assembly placed outside the vacuum of the glass envelope is the ____
Stator (magnets that turn rotor)
67
The function of the stator and rotor assembly is to ___
Rotate the anode
68
To increase the thermal loading capacity of the anode, the X-ray tube manufacturers must ____
Bond graphite to the back of the anode
69
The protective housing controls leakage and scatter radiation through ______
Absorption
70
Insulation of the high voltage components of the tube and absorption of the heat produced by X-ray production are achieved through the use of _____
Dielectric oil
71
What type of radiation is composed of photons NOT produced at the actual focal spot?
Off-focus and extra-focal
72
Leakage radiation from the lead-lined housing must NOT exceed
100 mR/hr at 1 meter
73
Radiation intensity is greater at the (anode/cathode) __________________________ side of the x-ray beam.
Cathode
74
The ANODE HEEL EFFECT is more noticeable with a (long/short) ______________________________ SID and a large Image Receptor.
Short
75
What 4 things are needed to make x-rays?
- source of electrons
- an appropriate target material
- high voltage
- vacuum
76
What two things control the size of the EFFECTIVE Focal Spot?
1. Size of the actual focal spot (which is controlled by the size of the filament)
2. Anode target angle
77
Decreasing the size of the filament will decrease the size of the:
Focal spot
78
The cathode side of the x-ray tube has a (negative/positive/neutral) __________________charge.
Negative
79
In an x-ray tube, the smaller the coil (filament), the (smaller/larger) __________________ the structure that can be imaged.
Smaller
80
Turning something into a gas is called:
Vaporization
81
Inside the x-ray tube, the component that is a shallow depression in the cathode assembly is called the:
Focusing cup
82
A space from which air and gases have been removed is called a (an):
Vacuum
83
Tungsten is the material of choice for the FILAMENT because it:
Has a high melting point and is difficult to vaporize
84
Rotating anode x-ray tubes allow (bigger/smaller) ________________________ exposures than stationary anode x-ray tubes.
Bigger
85
Large filaments (large focal spots) are used to image (larger/smaller) ______________________ body parts because the small filaments can’t take the stress of making big exposures on big body parts.
Larger
86
A cloud of electrons that forms when thermionic emission occurs is called a (an):
Thermionic cloud
87
Placing ______________________ on the back of rotating anodes can double the heat-loading capabilities
Graphite
88
The material of choice for the filament is usually _________________________________________ wire.
Tungsten
89
Routinely delaying the exposure (holding the rotor too long) while the filament is heating up (enduring maximum current) can shorten the tube life by about _________% to _________%.
50% to 60%
90
The x-ray tube consists of a cathode, anode, glass envelope and the:
Protective housing
91
When electrons are set free from the x-ray tube filament we sometimes say that they have been ____________________ off.
Boiled
92
The focusing cup is made of:
Nickel
93
An x-ray tube that is used to pulse the x-rays on and off quickly is called:
Grid pulsed or grid controlled
94
Increasing the speed that the anode rotates will (decrease/increase/not affect) _____________________ the heat loading capabilities of an x-ray tube.
Increase
95
What happens to vaporized electrons inside the x-ray tube? (List 2 things)
A. Reduces the tube vacuum
thus causing the tube to become gassy.
B. Deposit on the inside of the glass envelope
96
Most x-ray tubes have 2 filaments and this is known as a (an) _____________________________ FOCUS.
Dual Focus
97
One of the primary causes of premature tube failure is the radiographer’s habit of holding the:
ROTOR SWITCH TOO LONG BEFORE MAKING AN
EXPOSURE
98
What are the two things that the vaporized electrons that coat the inside of the x-ray tube can cause?
A. HIGH-VOLTAGE ARCHING
B. INCREASED FILTRATION OF THE PRIMARY X-RAY BEAM WHICH DECREASES TUBE EFFICIENCY
99
What makes the electrons move across the x-ray tube from cathode to anode?
High voltage
100
Any photons that escape from the x-ray tube housing except at the port are called:
Leakage radiation
101
The anode side of the x-ray tube has a (negative/positive/neutral) _________________ charge
Positive
102
When the target angle is decreased, (larger/smaller) __________________ Focal Spots can be achieved.
Smaller
103
The special glass used in x-ray tubes is:
Pyrex
104
In addition to tungsten as a target material, ____________________________________ is added to provide greater elasticity when the focal track expands rapidly due to the intense heat.
Rhenium
105
Inside the x-ray tube, the coil of wire is known as the:
Filament
106
The roughening of the anode during normal use is called:
Pitting
107
Pitting (decreases/increases) __________________ the efficiency of an x-ray tube.
Decreases
108
Special high speed anodes rotate between __________ - __________ r.p.m.
10,000 to 12,000
109
The x-ray tube component that is used to direct the electron cloud into a stream of electrons as it heads for the anode is called the:
Focusing cup
110
Failure to warm up the x-ray tube may cause the anode to:
Crack
111
Standard x-ray tube anodes normally rotate between __________ - __________ r.p.m.
3,200 to 3,600
112
The vast majority of high-output x-ray tubes are now made with __________________________ envelopes.
Metal
113
What are the three main reasons that tungsten is the main material of choice for the x-ray tube TARGET?
1. High atomic number
2. High melting point
3. Heat conducting ability
114
The ______________________________ Principle is used to reduce the effective area of the focal spot
Line - focus principle
115
The line-focus principle is used to reduce the effective area of the ______
Focal spot
116
The ______________________ Focal Spot is used to describe the area of the focal spot that is projected out of the x-ray tube towards the object being radiographed.
Effective focal spot
117
The ______________________________ permits the best resolution of detail while permitting as large an actual area as possible to act as a target (to increase thermal conductivity).
Line-focus principle
118
The term ________________________ refers to a very small Focal Spot, one that is a fraction of a millimeter in size.
Fractional focal spot
119
As the mA increases, so does the size of the Focal Spot. This is called:
Blooming
120
Some specialized mammography x-ray tubes use __________________________ as the target material.
Molybdenum
121
When the target angle is less than ______ degrees, the Effective Focal Spot is smaller than the Actual Focal Spot.
45 degrees
122
The point inside the x-ray tube where the x-ray photons are created is called the:
TARGET, FOCUS, FOCAL POINT, FOCAL SPOT or the FOCAL TRACK
123
The ANODE HEEL EFFECT is more noticeable with (large/small) _________________ Image Receptors (or x-ray films).
Large
124
Many x-ray tubes have a thinned area of the glass called the:
Window
125
In addition to tungsten, what two other materials are desirable for use as the x-ray tube filament?
Rhenium and molybdenum
126
What is the process called that produces particles that deposit on surfaces and reduces the vacuum within the x-ray tube?
Vaporization
127
Passing an electric current through a filament to the point where it heats up and causes electrons to leave the surface of the filament wire is called:
Thermionic emission
128
What causes the electrons in a thermionic cloud to move across the x-ray tube from cathode to anode?
High voltage
129
Rough handling of an old x-ray tube with a thin ____________________________ can cause it to break prematurely.
Filament
130
What part of the x-ray tube is responsible for narrowing the thermionic cloud as it is driven towards the anode?
Focusing cup
131
When the rotor is activated during an exposure, a higher current is sent to the filament - - - this increases the filament heating and is what causes most of the _________________________________ of the filament.
Vaporization
132
The (faster/slower) _____________________ the anode rotates, the better the heat dissipation.
Faster
133
Rotating anodes disks are composed of:
Molybdenum
134
A(An) ________________________-relieved anode dissipates heat much more efficiently than a standard x-ray tube anode.
Stress
135
The S.I.D. (Source to Image Receptor Distance) is measured from the ___________________________ to the Image Receptor
TARGET, FOCUS, FOCAL POINT, FOCAL SPOT or the FOCAL TRACK
136
Rotating anode x-ray tubes have much greater ________________________ capacities than stationary anode x-ray tubes.
Heat loading
137
The Line – Focus Principle is used to ___________ the effective area of the focal spot.
Reduce
138
The use of the Line-Focus Principle causes a problem known as the:
Anode heel effect
139
The intensity of radiation emitted by the x-ray tube target varies by about _________% between the anode side and the cathode side.
45%
140
With the Anode Heel Effect, the (anode/cathode)______________________ side has a more intense x-ray beam.
Cathode
141
If a high-speed anode tube-housing is quickly rotated from one position to another (for example, from horizontal to vertical), the ________________________ Effect can cause trauma to the anode disk and bearings, causing destruction of the tube.
Gyroscopic
142
A metal envelope x-ray tube has a longer tube life because they eliminate the problems of:
Tungsten evaporation
143
What are the three functions of the positive side of the x-ray tube? (Anode side)
A. target surface
B. primary thermal conductor
C. Conducts the high voltage from the cathode back into the x-ray generator
