Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Radiographic Exposures Test 1 > Chapter 5 > Flashcards

Chapter 5 Flashcards

1
Q

The x-ray tube consists of a _______ and an ______ enclosed within an _______, and then encased in a _______.

A

cathode; anode; envelope; protective housing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

An X-ray tubes life can be significantly extended by ________.

A

Proper care and handling by professional radiographers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Is the cathode the positive or negative side of the x-ray tube?

A

Negative

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the function of the cathode?

A

To produce a thermionic cloud, conduct the high voltage to the gap between cathode and anode, and focus the electron stream as it heads for the anode.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

The cathode assembly consists of?

A

The filament or filaments, focusing cup, and associated wiring.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a filament?

A

A small coil of thin tho rusted tungsten wire.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How thick is the filament wire?

A

0.1-0.2 mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the dimensions of the filament?

A

1-2mm wide by 7-15mm long.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

_________ is the material of choice because of its high melting point.

A

Tungsten

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the melting point of tungsten?

A

3,370*C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are two desirable materials to use as a filament other than tungsten?

A

Rhenium & molybdenum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why is tungsten not easily vaporized a good material to used in a cathode?

A

Vaporization produces particles that deposit on other surfaces and reduce the vacuum witching the tube.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is another name for x-ray tubes that have dual filaments?

A

Dual-focus arrangement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the function of the filament?

A

To provide sufficient resistance to the flow of electrons so that the heat produces will cause thermionic emission to occur.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What temperature does tungsten need to reach to exhibit significant thermionic emission?

A

Above 2,200*C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Older tubes are much more sensitive to ______ and a _____ that is jarred can break prematurely.

A

Rough handling; thin filament

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is an average diagnostic x-ray tube filament life?

A

6-9 hours (10,000-20,000 exposures)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the primary cause of premature turn failure?

A

The radiographer’s habit of holding the rotor switch prior to making exposures. Every second the rotor switch is depressed, life is removed from the filament.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Routinely delayed exposures while the filament is enduring maximum current can shorten tube life by ___-___% (To 5,000-12,000 exposures)

A

50;60

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Single-phase generators are usually capable of initiating exposure within ____ milliseconds.

A

10 (0.01 second)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

High-frequency generators are usually capable of initiating exposure within ___ millisecond.

A

1 (0.001 second)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Who developed the cathode using a hot filament?

A

William D. Coolidge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

When was the Coolidge tube developed?

A

1915

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What other development did Coolidge contribute to radiography other than the hot filament?

A

The focusing cup, the imbedded anode target, and various anode cooking devices.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Why is the focusing cup?

A

A shallow depression in the cathode assembly designed to house the filament.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the focusing cup made of?

A

Nickel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the focusing cup’s purpose?

A

To narrow the thermionic cloud as it is driven toward the anode.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Why do electrons have a tendency to diverge rather than travel in straight lines?

A

Because they possess a negative charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is space charge effect?

A

As more electrons build up in the area of the filament, their negative charge begin to oppose emission of additional electrons. It also limits x-ray tubes to maximum mA range of 1,000-1,200.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is saturation current?

A

Affects the efficiency of the x-ray tube. As kVp increases, a grater percentage of the thermionically emitted electrons are driven toward the anode. The filament amperage curve flattens out when the kVp is driving the entire thermionic cloud toward the anode. Saturation current is achieved when there are no further thermionic electrons to be driven toward the anode.

31
Q

The anode is the positive or negative side of the x-ray tube?

A

Positive

32
Q

Why are the anode side of the x-ray tubes 3 functions?

A

-Serves as a target surface for the high voltage electrons from the filament(becoming the source of x-ray photons)
-it conducts the high voltage form the cathode back into the x-ray generator circuitry
-it serves as the primary thermal conductor

33
Q

The ________________ is where the high-speed electrons from the filament are suddenly stopped, resulting in the production of x-ray photons.

A

Anode target surface

34
Q

The anode assembly consists of?

A

The anode, static and rotor and serves as the path for the high-voltage flow during exposure.

35
Q

What are the two types of anodes?

A

Stationary anodes and rotating anodes

36
Q

When we’re rotating anodes developed?

A

1936

37
Q

How long is a given area of the target bombarded in modern rotating anodes?

A

7-50 microseconds

38
Q

The _______ the anode rotates, the better the heat dissipation.

A

Faster

39
Q

Stationary anodes comprise _______________ imbedded in a ___* angled end of a copper rod.

A

Rhenium-alloyed tungsten; 45

40
Q

Rotating anode disks range from ____ to ____ cm in diameter and comprise ____________.

A

5; 13; molybdenum

41
Q

Tungsten is the metal of choice for the source of x-ray photons for what three reasons?

A
  • High atomic number(74)
  • High melting point
  • Heat-conducting ability
42
Q

During normal use, the focal track reaches a temperature between _________C and _______C

A

1,000; 2,000

43
Q

What does using an anode warm-up procedure designed to do?

A

To bring the anode heat form room temperature to near the range of operation.

44
Q

A tape measure attached to the side or bottom of a tube collimating may begin at 12 cm because?

A

The target is considered the point source of x-ray photons and it is from this point all tube-to-object and image-receptor distance are measured.

45
Q

Line-focus principle is used to

A

Reduce the effective area of the focal spot. This permits the vets resolution of detail while permitting as large an actual area as possible

46
Q

As the actual focal-spot size increases, the effective focal-spot size ____________.

A

Also Increases

47
Q

When the target angle is less than ____*, the effective focal spot is smaller than the actual focal spot.

A

45

48
Q

What is the most common diagnostic radiography target angle is?

A

12*

49
Q

When the target angle is decreased, ________ focal spots can be achieved.

A

Smaller

50
Q

Why is a disadvantage of extremely small target angles?

A

The geometry of the angle can limit the size of the primary beam field at short source-to-image receptor distances.

51
Q

To cover a 14”x17” field at 40”, a minimum of ____* target angle is required.

A

12

52
Q

Target angles of ______ than 14* have been shown to produce some degree of ______ as they age

A

Less; cutoff

53
Q

Why are x-ray focal spots rectangular?

A

Because the line-focus principle applies only in the direction is the angle.

54
Q

X-ray tube targets must be ________ to maintain the small effective focal-spot size in the horizontal direction, usually not over 2 mm.

A

Narrow

55
Q

The line-focus principle permits the actual focal spot’s vertical dimension to as much as 6 mm to gain __________________________________.

A

Maximum thermal conductivity

56
Q

The effective focal spot’s vertical dimension is the only one stated as the ______________.

A

Focal-spot size

57
Q

Who establishes standards for focal-spot size?

A

The National Electrical Manufacturers Association (NEMA)

58
Q

The ________ is the only part of the cathode or anode assemblies that is located _________ the vacuum of the envelope.

A

Outside

59
Q

Where is the rotor located?

A

Inside the stator and inside the envelope

60
Q

What is the rotor comprised of?

A

A hollow cylinder or cuff that is attached ti the anode disk by a molybdenum shaft.

61
Q

Common rotating anodes revolve at _____-______ revolutions per minute.

A

3,200-3,600

62
Q

A common cause of then failure is _______________ caused by long use at high temperatures.

A

Bad bearings

63
Q

What is the primary function of the envelope?

A

to maintain the vacuum between the cathode and anode

64
Q

What does the removal of air permit from the vacuum pump do?

A

permits electrons to flow from cathode to anode without encountering the gas atoms of air and greatly increases the efficiency of the tube’s operation

65
Q

Modern x-ray tubes must be mounted inside what?

A

a protectives housing

66
Q

What does the housing control?

A

leakage and scatter radiation, isolates the high voltages, and provides a means to cool the tube

67
Q

When x-ray photons are produced in the anode, how are they emitted?

A

isotropically (in all directions)

68
Q

What is leakage radiation?

A

any photons that escape from the housing except from the port

69
Q

What must leakage radiation not exceed?

A

100 mR/hr at 1 meter

70
Q

Off-radiation may contribute as much as __-__ percent of the total beam.

A

25-30

71
Q

What are the three types of rating charts available to help radiographers avoid thermal damage to x-ray tubes?

A

radiographic tube rating charts, anode cooling charts, and housing cooling charts

72
Q

What do anode cooling charts permit?

A

the calculation of the time necessary for the anode to cool enough for additional exposures to be made

73
Q

What is the formula for calculating heat units?

A

kVp x mA x time x rectification constant

Radiographic Exposures Test 1 (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions