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Principles of Radiographic Exposure > X-ray Tube > Flashcards

X-ray Tube Flashcards

1
Q

What does the X-ray tube cause?

A

Causes process of ionization to occur

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2
Q
A
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3
Q

On the X-ray tube, what charges are anode and cathode?

A

Anode= positive

Cathode= negative

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4
Q

Where does radiation creation start?

A

At the control panel

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5
Q
A
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6
Q

What do you need in order to produce x-ray?

A
  1. Source of electrons
  2. Acceleration of electrons (get them moving)
  3. Decelerate the electrons (stop them)
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7
Q

What does the X-ray tube do?

A

Provides the electrical productions of x-rays

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8
Q

What are the 4 parts the X-ray tube consists of?

A
  1. Cathode (negative side - will provide us electrons)
  2. Anode (positive side - attracts protons)
  3. Protective housing
  4. Evelope (glass)
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9
Q
A
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10
Q

What are the functions of the cathode/negative side?

A
  1. Produce thermionic cloud
    1. Conduct high voltage to gap between anode and cathode
    1. Focus the electron stream as they travel through anode side
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11
Q

What’s included in the cathode assembly?

A
  1. Filament
  2. Focusing cup
  3. Associated wiring
  4. Filament circuit
  5. High voltage circuit
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12
Q

What is the main metal of the filament material?

A

Tungsten (atomic # 74)

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13
Q

What are the properties of tungsten?

A
  • High melting point
  • high atomic #
  • diffucult to vaporize
  • heat conducting ability
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14
Q

What is the melting point of tungsten?

A

3370

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15
Q

What are other good choices for filament material besides tungsten?

A

Rhenium and molybdenum

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16
Q

Describe filament

A

Small coil of tungsten

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17
Q

What does tungsten do?

A
  • Acts as a resistance to flow of electrons
  • Produces heat by electrons flowing through the coil
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18
Q

What is thermionic emission?

A

Boiling off electrons

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19
Q

What is the minimum heat to boil off electrons/for thermionic emission to occur?

A

2,220°C minimum

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20
Q

Describe thermionic cloud (electron cloud)

A

Made from electrons boiled off the filament

  • Electrons are attracted to the anode (+) and accelerates to the anode side
    note: Some electrons flow back to the filament wire. A very small amount of electrons vaporize from the filament line and glass envelope (gassy tube)
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21
Q

How many filament wires does the X-ray tube have?

A

2

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22
Q

Dual focus

A

Allows for small and large focal spot size

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23
Q

The smaller the FSS…

A

The better the detail

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24
Q

What is the focusing cup made out of?

A

Nickel

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25
Q

What is the purpose of the focusing cup?

A
  • To streamline the thermionic cloud as its driven towards the anode
  • house the filament coils
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26
Q

What kind of charge does the focusing cup have?

A

Negative

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27
Q

What is the space charge effect?

A

As more and electrons are “boiled” off the filament, their negative charges begin to oppose the emission of additional electrons

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28
Q

How is saturation current achieved?

A

When there are no further thermionic electrons to be driven towards the anode. As kVp increases, a greater percentage of electrons are driven towards the anode

29
Q

What are the functions of the anode side (positive side)?

A
  1. Attracts the electrons to the anode side
  2. Serves as a target to stop electron stream
  3. Source of photons (x-radiation)
  4. Serves as primary thermal conductor
30
Q

What are the components of the anode assembly?

A
  • Target
  • Stator
  • Rotor
31
Q

What is the job of the target/anode target?

A

Decelerate electrons

32
Q

What are the 2 types of targets?

A

Stationary and rotating

33
Q

What is the x-ray angle of the target?

A

7-17° angle — common is 12°

34
Q

What metals are included in anode layering?

A

Tungsten (rhenium is added to allow expansion of the focal track when rapidly heated)

&

molybdenum and/or graphite (allows for heat cunducting)

35
Q

Describe the rotating target

A

Disc-shaped

5-13 cm in diameter

36
Q

With a rotating target, the faster the rotation…

A

The better heat dissipation

37
Q

What is the average target rpm of the rotating target?

What is the fast speed target rpm of the rotating target?

A

Average Target= 3200-3600rpm

Fast Speed Target= 10,000-12,000 rpm

38
Q
A
39
Q

What is the temperature of the focal tract after production of photons?

A

1,000 to 2,000° average

40
Q

What are the portions where the electrons strike the target called?

A
  • Focal track
  • Focal point
  • Focal spot
  • Source of photons
41
Q

What is the line focusing principle?

A

Allows the best resolution (detail) while permitting a large area of the focal track to be struck by electrons

(why? Because a minimum heat 1,000-2,000°C created)

42
Q

What happens during the stationary line focal principle?

A

Target angle decreased, effective focal spot size decreased

43
Q

Same target angle: smaller FSS…

A

Smaller the EFSS = better detail

44
Q

What does the line focus principle do?

A
  • Allows for
45
Q

What is the anode heel effect?

A
46
Q

Anode heel effect is more prominent at…

A
47
Q

What does the stator do?

A
48
Q

Describe stator

A
49
Q

When the rotor switch is activated, what happens?

A
50
Q

If the stator fails…

A
51
Q

Describe rotor

A
52
Q

What is the common/average speed of rotor?

What is the highest speed of the rotor?

A

Common= 3,200-3,600 rpm

high speed= 10,000 to 12,000 rpm

53
Q

Describe the envelope

A
  • Pyrex glass or metal
  • 10” ling
  • 6” central diameter
  • houses tube part
  • the window
  • maintains a vacuum
54
Q

What does the window do?

A

Allows for photons to pass out of tube

(thinner section of the envelope, less absorption of the photons)

55
Q

What does the vacuum do?

A
  • Removal of the air permits electrons to flow from cathode to anode without interacting with gas atoms
  • increases the radiation output or efficiency
56
Q

What was created in the late 1930s?

A

X-ray tube

57
Q

What type of exam was done in the 1940s?

A
58
Q

What does the protective housing do?

A
  • Controls leakage and scatter radiation
  • isolates high voltages
  • provides means to cool the tube
59
Q

The housing is made of what to control leakage radiation and scatter radiation?

A
60
Q

What is leakage radiation?

A

Any photons that escapes from the housing except the window

61
Q

What happens during leakage radiation?

A
  • Radiation emitted from the target isotropically (in all directions)
  • primary beam (useful beam) exits out of the window
62
Q

What must leakage radiation not exceed?

A
63
Q

What fills the space between envelope and housing in high voltage isolation and tube cooling?

A

Dielectric oil

64
Q

What does dielectric oil act as?

A
65
Q

How is off-focus radiation created?

A

From photons created in the tube somewhere besides on the focal track “ghostly image”

66
Q

What does the warm up procure do?

A
  • Gradually warms the anode
  • prevents cracking
  • helps maintain vacuum
67
Q

Recommendations for extending tube life

A
68
Q
A

Principles of Radiographic Exposure (18 decks)

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