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Pre Exposure > The X-ray tube > Flashcards

The X-ray tube Flashcards

1
Q

What’s in the internal?

A

Cathode and Anode

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2
Q

What is external?

A

Support structure
Protective housing
Glass or metal enclosure

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3
Q

What are the conditions that make a xray production possible?
(4)

A

-source of electrons
-vacuum
-high voltage
-apporiat target material

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4
Q

what side is the cathode?

A

negative side

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5
Q

What are the cathode’s functions?
(3)

A

-produce a thermionic cloud
-Conduct high voltage between the cathode and anode
-Focus the electron stream towards the anode

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6
Q

What does the cathode assembly consist of?

A

Filament
Focusing cup
Associated wiring

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7
Q

What is filament?

A

Small coil of thoriated tungsten wire
-0.1 to 2.0 mm thick
-Could also be made of rhenium and Molybdenum

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8
Q

Most xrays tubes have..

A

dual focus arrangement (2 filaments)

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9
Q

What is the function of the filament?
(Sufficient resistance?)

A

-Provides sufficient resistance to the flow of electrons so that the heat produced will cause an thermionic cloud

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10
Q

What is the space charge effect?

A

As more electrons build up in the filament there negative charges begin to oppose the emission of more electrons

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11
Q

What is the focusing cup made of?

A

nickel

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12
Q

What does the focusing up do?

A

narrows the thermionic cloud

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13
Q

Its a shallow depression in the cathode assembly designed to house the filament?

A

Focusing cup

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14
Q

What does the grid biased tubes do?
(grid-pulsed or grid-controlled)

A

Focusing cup pulses between negative and positive charge to remove electrons from use (rapid)

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15
Q

What causes tube failure?

A

High voltage arcing which is short circuit in the tube (glass cracking)

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16
Q

Types of tube failure

A

Breaking of the filament
Rough handling the equipment (jarring)
Holding the rotor switch to long prior to exposure

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17
Q

Routinely delaying exposure can shorten tube life by

A

50-60%

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18
Q

What side is the anode?

A

Positive side

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19
Q

Anode functions?

A

-Target surface for electrons
-Conduct high voltage from the cathode back into the xray generator
-Thermal conductor

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20
Q

What is the anode assembly?

A

Anode (TARGET)
Stator
Rotor

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21
Q

What are the two types of anode

A

Stationary and Rotating

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22
Q

What does the rotating anode do?

A

Turn during the exposure

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23
Q

What is the common rotating anodes revolve at?

A

3,200-3,600 rpm

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24
Q

What is the high speed anodes revolve at?

A

10,000-12,000 rpm

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25
What is the focal track made of?
tungsten rhenium alloy
26
Why is tungsten a metal of choice for anode ?
High atomic number #74 High melting point Heat conducting ability
27
What is pitting?
Normal use of rotating the anode and will eventually vaporize the target material -reduces the tube efficiency
28
What is cracking?
its a failure to warm up the tube range of operation before use
29
What is called when the anode relief itself from stress?
Stress relief
30
What can the focal track also be called?
-target -focus -focal point -focal spot
31
What is actual focal spot?
The physical area of the focal track that is impacted
32
What is effective focal spot?
area of the focal spot that is projected out of the tube toward the object being radiographed
33
What does the line-focus principal do?
its used to reduce the effective area of the focal spot
34
Effective focal spot is controlled by?
-size of the actual focal spot -size of filament -anode target angle
35
What is the limits of the xray tube mA ranges?
1,000-2,000 mA
36
To cover a 14x17 IR at 40" you need a minimum target angle of...
12 degrees
37
The use of the line-focus principle causes a problem that is known as...
anode heel effect
38
Why is the anode heel effect a problem for the line-focus principle?
Bc of its geometry of an angled anode target which the radiation is greater on the cathode side
39
Anode heel effect is more noticeable at...
-short SID -Large image receptor -small focal spot
40
The anode side is (less thick or thicker)
less thick
41
The cathode side is (less thick or thicker)
thicker
42
What is the stator?
Uses magnets to turn on the rotor
43
What does the stator turn and where is it located?
turns the anode and its located outside the vacuum of the envelope
44
If the stator fails the rotor...
Won't turn the anode and result in melting the spot on target
45
Where is the rotor located?
its located inside the stator and inside the envelope
46
How does the rotor look like ?
Hollow copper cylinder or cuff that is attached to the anode disk by a molybdenum shaft
47
What is inside the rotor?
Contains sliver plated steel ball bearings around the shaft and is anchored to the envelope
48
What is rotor failures?
high- speed harmonic damage which is caused by the tone produced by their rotating (5,000 and 7,000 rpm)
49
If a high speed anode tube housing is quickly rotated from one position to another, what is it called?
gyroscopic effect
50
What does the gyroscopic effect produced?
the centrifugal force of the rotation
51
Another rotor failure is...
bad bearings because of long use at high temperature
52
What is in the envelope ?
the entire cathode and anode assembly EXECPT the STATOR enclosed within a glass
53
Why is metal envelopes a increasingly more common choice than glass?
Prolong tube life because it eliminates problem of tungsten vaporization
54
What is the vacuum's function?
Removable of air which permits electrons to flow from cathode to anode
55
What does the housing control?
leakage scatter radiation isolates the high voltage Cools the tube
56
When xray photons are produced at the anode they are emitted
isotopically (in all directions)
57
The primary beam consists of photons emitted
throughout the window
58
Leakage radiation must not exceed...
100mR/hr at 1 meter
59
What is dielectric oil used for?
-its used to fill space between the envelope and the tube housing -insulated high voltage components from the tube housing
60
What is off-focus or extrafocal radiation?
its photons that were not produced at the focal spot
61
What causes ghosting structures?
scattered electrons or photons when they have sufficient energy remaining and strike another object in the tube
62
When talking about focal track what does it represent?
Represents the circular path that will be impacted by electron stream
63
Xrays are produced and most are emitted at angles between...
45 and 90 degrees

Pre Exposure (11 decks)

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