The X-Ray Tube (Chapter 5) Flashcards
What are the internal X-ray tube components?
Cathode and Anode
What are the external X-ray tube components?
- Support structure
- Protective housing
- Glass or metal enclosure
X-ray production is only possible under these conditions:
- Source of electrons
- Appropriate target material
- High voltage
- Vacuum
Cathode side is _____ (negative, positive)
Negative
What is the function of a cathode?
- To produce thermionic cloud ⭐️⭐️⭐️⭐️
- Conduct high voltage to gap between cathode and anode
- Focus electron stream towards the anode
Cathode assembly consists of: (list 3)
- Filaments
- Focusing cup
- Associated wiring
What is a filament?
Small coil of thoriated tungsten wire
Why is tungsten important?
- High melting point
- Difficult to vaporize
What is the function of a filament?
resistance to the flow of electrons
so that the heat produced will cause thermionic emission
What is the space charge effect?
As more and more electrons are produced at the filament, their negative charges don’t allow any additional electrons
What does the focusing cup do?
Narrows the thermionic cloud
What is the focusing cup?
Small cup with wire
Focusing cup pulsed between negative and positive charge to remove electrons from use is called ___?
Grid -pulsed or Grid controlled
What are the functions of the anode? (List 3)
1.Target surface for electrons
2. Conducts high voltage from the cathode back into the X-ray generator
3. Primary thermal conductor
What does the Anode Assembly consist of?
- Anode (target)
- Stator
- Rotor
List 2 types of Anode (Targets)
- Stationary
- Rotating
Function of a rotating anode?
- Source of X-ray photons
- Primary thermal conductor
Common rotating anodes revolve at ____ ?
3,200 - 3,600 rpm
High speed anodes revolve at _____?
10,000 - 12,000 rpm
Tungsten is the metal of choice for 3 reasons
- High atomic number (74)
- High melting point
- Heat-conducting ability
What is tungsten’s atomic number?
74
What is pitting?
Normal use of a rotating anode will eventually vaporize the target track material
(Reduces the efficiency of the tube)
What is cracking?
Failure to warm the tube up to range of operation before use can crack the anode
What is the focal track?
The circular path that will be impacted by the electron stream and where the X-ray photons are produced
What is the actual focal spot?
The physical area of the focal track that is impacted by
What is the effective focal spot?
Area of the focal spot that is projected out of the tube toward the object being radiographed
The effective focal spot is controlled by:
- The actual focal spot
- Size of filament
- Anode target angle
What is the Anode Heel Effect?
Because of the geometry of an angled anode target, the radiation intensity is greater on the cathode side.
The anode heel effect is most noticeable at: (list 3)
- Short SID
- Large image receptor
- Small focal spot
The only part of the cathode or anode assemblies that is located outside the vacuum or the envelope
Stator
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
Where is the Rotor located?
Located inside the stator and inside the envelope
The rotor revolves at _____ rpm
3,200 - 3,600
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)
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
The envelope is made up of what kind of glass?
Heat resistant Pyrex glass
The primary function of the envelope ?
To maintain the vacuum between the cathode and anode
The protective housing controls: (list 3)
- Leakage and scatter radiation
- Isolates the high voltages
- Provides a mean to cool the tube
The protective housing is made up of :
Made of steel and lined with lead
When x-ray photons are produced at the anode, they are emitted _____ (in all directions)
Isotropically
The primary beam consists of:
Photons emitted through the window
Leakage radiation must not exceed _____ mR/hr at ____ meter
100 mR/hr at 1 meter
Off focus or extra focal radiation is:
Photons that were not produced at the focal spot
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.
High voltage electrons striking the focal spot produce ____ electrons or photons
Scattered
List 3 cathode filament materials:
- Tungsten
- Rhenium
- Molybdenum
Filament materials are chosen primarily for their___?
High melting points & difficult to vaporize
List 3 things that would affect the production of a thermionic cloud
- Filament diameter
- Filament length
- Filament temperature
A filament may break due to ____
Vaporization
Driving the thermionic cloud from the cathode to the anode requires ____
High - Voltage
The cathode focusing cup has a _____ charge
Negative
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
X-ray photon production occurs at the
Anode
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
Pitting of the anode commonly occurs ____
With extended use
Melting of the anode commonly occurs when …
When the stator fails and the rotor ceases to turn
Cracking of the anode typically occurs when …
When a cold anode is hit with a high kVp exposure
The exact point on the anode where the x-ray beam comes out is the ____
Effective focal spot
The physical area of a rotating anode focal track, affected by the cathode electron beam, is the ____
Actual focal spot
The area of the focal spot that is projected out of the tube toward the object being radiographed is the
Effective focal spot
The actual focal spot is controlled by the
Length of the filament
The most common diagnostic radiography x-ray tube target angle is ___ degrees
12
As the actual focal spot size increases, the effective focal spot size _____
(Decreases, increases, doesn’t change)
Increases (they are directly related)
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
The use of the line-principle causes a problem knows as the _____ effect
Anode heel effect
The only portion of the anode assembly placed outside the vacuum of the glass envelope is the ____
Stator (magnets that turn rotor)
The function of the stator and rotor assembly is to ___
Rotate the anode
To increase the thermal loading capacity of the anode, the X-ray tube manufacturers must ____
Bond graphite to the back of the anode
The protective housing controls leakage and scatter radiation through ______
Absorption
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
What type of radiation is composed of photons NOT produced at the actual focal spot?
Off-focus and extra-focal
Leakage radiation from the lead-lined housing must NOT exceed
100 mR/hr at 1 meter
Radiation intensity is greater at the (anode/cathode) __________________________ side of the x-ray beam.
Cathode
The ANODE HEEL EFFECT is more noticeable with a (long/short) ______________________________ SID and a large Image Receptor.
Short
What 4 things are needed to make x-rays?
- source of electrons
- an appropriate target material
- high voltage
- vacuum
What two things control the size of the EFFECTIVE Focal Spot?
- Size of the actual focal spot (which is controlled by the size of the filament)
- Anode target angle
Decreasing the size of the filament will decrease the size of the:
Focal spot
The cathode side of the x-ray tube has a (negative/positive/neutral) __________________charge.
Negative
In an x-ray tube, the smaller the coil (filament), the (smaller/larger) __________________ the structure that can be imaged.
Smaller
Turning something into a gas is called:
Vaporization
Inside the x-ray tube, the component that is a shallow depression in the cathode assembly is called the:
Focusing cup
A space from which air and gases have been removed is called a (an):
Vacuum
Tungsten is the material of choice for the FILAMENT because it:
Has a high melting point and is difficult to vaporize
Rotating anode x-ray tubes allow (bigger/smaller) ________________________ exposures than stationary anode x-ray tubes.
Bigger
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
A cloud of electrons that forms when thermionic emission occurs is called a (an):
Thermionic cloud
Placing ______________________ on the back of rotating anodes can double the heat-loading capabilities
Graphite
The material of choice for the filament is usually _________________________________________ wire.
Tungsten
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%
The x-ray tube consists of a cathode, anode, glass envelope and the:
Protective housing
When electrons are set free from the x-ray tube filament we sometimes say that they have been ____________________ off.
Boiled
The focusing cup is made of:
Nickel
An x-ray tube that is used to pulse the x-rays on and off quickly is called:
Grid pulsed or grid controlled
Increasing the speed that the anode rotates will (decrease/increase/not affect) _____________________ the heat loading capabilities of an x-ray tube.
Increase
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
Most x-ray tubes have 2 filaments and this is known as a (an) _____________________________ FOCUS.
Dual Focus
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
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
What makes the electrons move across the x-ray tube from cathode to anode?
High voltage
Any photons that escape from the x-ray tube housing except at the port are called:
Leakage radiation
The anode side of the x-ray tube has a (negative/positive/neutral) _________________ charge
Positive
When the target angle is decreased, (larger/smaller) __________________ Focal Spots can be achieved.
Smaller
The special glass used in x-ray tubes is:
Pyrex
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
Inside the x-ray tube, the coil of wire is known as the:
Filament
The roughening of the anode during normal use is called:
Pitting
Pitting (decreases/increases) __________________ the efficiency of an x-ray tube.
Decreases
Special high speed anodes rotate between __________ - __________ r.p.m.
10,000 to 12,000
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
Failure to warm up the x-ray tube may cause the anode to:
Crack
Standard x-ray tube anodes normally rotate between __________ - __________ r.p.m.
3,200 to 3,600
The vast majority of high-output x-ray tubes are now made with __________________________ envelopes.
Metal
What are the three main reasons that tungsten is the main material of choice for the x-ray tube TARGET?
- High atomic number
- High melting point
- Heat conducting ability
The ______________________________ Principle is used to reduce the effective area of the focal spot
Line - focus principle
The line-focus principle is used to reduce the effective area of the ______
Focal spot
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
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
The term ________________________ refers to a very small Focal Spot, one that is a fraction of a millimeter in size.
Fractional focal spot
As the mA increases, so does the size of the Focal Spot. This is called:
Blooming
Some specialized mammography x-ray tubes use __________________________ as the target material.
Molybdenum
When the target angle is less than ______ degrees, the Effective Focal Spot is smaller than the Actual Focal Spot.
45 degrees
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
The ANODE HEEL EFFECT is more noticeable with (large/small) _________________ Image Receptors (or x-ray films).
Large
Many x-ray tubes have a thinned area of the glass called the:
Window
In addition to tungsten, what two other materials are desirable for use as the x-ray tube filament?
Rhenium and molybdenum
What is the process called that produces particles that deposit on surfaces and reduces the vacuum within the x-ray tube?
Vaporization
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
What causes the electrons in a thermionic cloud to move across the x-ray tube from cathode to anode?
High voltage
Rough handling of an old x-ray tube with a thin ____________________________ can cause it to break prematurely.
Filament
What part of the x-ray tube is responsible for narrowing the thermionic cloud as it is driven towards the anode?
Focusing cup
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
The (faster/slower) _____________________ the anode rotates, the better the heat dissipation.
Faster
Rotating anodes disks are composed of:
Molybdenum
A(An) ________________________-relieved anode dissipates heat much more efficiently than a standard x-ray tube anode.
Stress
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
Rotating anode x-ray tubes have much greater ________________________ capacities than stationary anode x-ray tubes.
Heat loading
The Line – Focus Principle is used to ___________ the effective area of the focal spot.
Reduce
The use of the Line-Focus Principle causes a problem known as the:
Anode heel effect
The intensity of radiation emitted by the x-ray tube target varies by about _________% between the anode side and the cathode side.
45%
With the Anode Heel Effect, the (anode/cathode)______________________ side has a more intense x-ray beam.
Cathode
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
A metal envelope x-ray tube has a longer tube life because they eliminate the problems of:
Tungsten evaporation
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
