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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?

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?

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?

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 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
Q

What is the focal track made of?

A

tungsten rhenium alloy

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26
Q

Why is tungsten a metal of choice for anode ?

A

High atomic number #74
High melting point
Heat conducting ability

27
Q

What is pitting?

A

Normal use of rotating the anode and will eventually vaporize the target material
-reduces the tube efficiency

28
Q

What is cracking?

A

its a failure to warm up the tube range of operation before use

29
Q

What is called when the anode relief itself from stress?

A

Stress relief

30
Q

What can the focal track also be called?

A

-target
-focus
-focal point
-focal spot

31
Q

What is actual focal spot?

A

The physical area of the focal track that is impacted

32
Q

What is effective focal spot?

A

area of the focal spot that is projected out of the tube toward the object being radiographed

33
Q

What does the line-focus principal do?

A

its used to reduce the effective area of the focal spot

34
Q

Effective focal spot is controlled by?

A

-size of the actual focal spot
-size of filament
-anode target angle

35
Q

What is the limits of the xray tube mA ranges?

A

1,000-2,000 mA

36
Q

To cover a 14x17 IR at 40” you need a minimum target angle of…

A

12 degrees

37
Q

The use of the line-focus principle causes a problem that is known as…

A

anode heel effect

38
Q

Why is the anode heel effect a problem for the line-focus principle?

A

Bc of its geometry of an angled anode target which the radiation is greater on the cathode side

39
Q

Anode heel effect is more noticeable at…

A

-short SID
-Large image receptor
-small focal spot

40
Q

The anode side is
(less thick or thicker)

A

less thick

41
Q

The cathode side is
(less thick or thicker)

A

thicker

42
Q

What is the stator?

A

Uses magnets to turn on the rotor

43
Q

What does the stator turn and where is it located?

A

turns the anode and its located outside the vacuum of the envelope

44
Q

If the stator fails the rotor…

A

Won’t turn the anode and result in melting the spot on target

45
Q

Where is the rotor located?

A

its located inside the stator and inside the envelope

46
Q

How does the rotor look like ?

A

Hollow copper cylinder or cuff that is attached to the anode disk by a molybdenum shaft

47
Q

What is inside the rotor?

A

Contains sliver plated steel ball bearings around the shaft and is anchored to the envelope

48
Q

What is rotor failures?

A

high- speed harmonic damage which is caused by the tone produced by their rotating
(5,000 and 7,000 rpm)

49
Q

If a high speed anode tube housing is quickly rotated from one position to another, what is it called?

A

gyroscopic effect

50
Q

What does the gyroscopic effect produced?

A

the centrifugal force of the rotation

51
Q

Another rotor failure is…

A

bad bearings because of long use at high temperature

52
Q

What is in the envelope ?

A

the entire cathode and anode assembly EXECPT the STATOR enclosed within a glass

53
Q

Why is metal envelopes a increasingly more common choice than glass?

A

Prolong tube life because it eliminates problem of tungsten vaporization

54
Q

What is the vacuum’s function?

A

Removable of air which permits electrons to flow from cathode to anode

55
Q

What does the housing control?

A

leakage
scatter radiation
isolates the high voltage
Cools the tube

56
Q

When xray photons are produced at the anode they are emitted

A

isotopically (in all directions)

57
Q

The primary beam consists of photons emitted

A

throughout the window

58
Q

Leakage radiation must not exceed…

A

100mR/hr at 1 meter

59
Q

What is dielectric oil used for?

A

-its used to fill space between the envelope and the tube housing
-insulated high voltage components from the tube housing

60
Q

What is off-focus or extrafocal radiation?

A

its photons that were not produced at the focal spot

61
Q

What causes ghosting structures?

A

scattered electrons or photons when they have sufficient energy remaining and strike another object in the tube

62
Q

When talking about focal track what does it represent?

A

Represents the circular path that will be impacted by electron stream

63
Q

Xrays are produced and most are emitted at angles between…

A

45 and 90 degrees

Pre Exposure (9 decks)

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