CHAPTER 6—THE X-RAY TUBE
TRUE/FALSE
1. The cathode is the negative side of the x-ray tube.
ANS: T
DIF: Easy
2. The filament is set in the cathode assembly outside of the focusing cup.
ANS: F
DIF: Medium
3. Electrons in the thermionic cloud are driven from cathode to anode with 100% efficiency.
ANS: F
DIF: Easy
4. Most x-ray tubes have a dual-focus arrangement.
ANS: T
DIF: Easy
5. To prolong x-ray tube life, the exposure switch should be partially depressed for a few seconds before
complete depression occurs.
ANS: F
DIF: Medium
6. Filament saturation occurs when the negative charge of the electron cloud opposes the emission of
additional electrons from the filament.
ANS: F
DIF: Difficult
7. The faster the anode rotation, the better the heat dissipation.
ANS: T
DIF: Medium
8. Like the cathode, the anode is comprised of a single metal called tungsten.
ANS: F
DIF: Medium
9. The line-focus principle is used to reduce the actual area of the focal spot.
ANS: F
DIF: Medium
10. When the target angle is less than 45°, the effective focal spot is smaller than the actual focal spot.
ANS: T
DIF: Medium
11. As the anode target angle increases, the primary beam field size increases.
ANS: T
DIF: Medium
12. In radiology, the term focal spot size refers to the effective focal spot.
ANS: T
DIF: Medium
13. According to the anode heel effect, the radiation intensity is greater on the anode side.
ANS: F
DIF: Easy
14. The entire cathode and anode assemblies are enclosed within the glass envelope.
ANS: F
DIF: Medium
15. Off-focus radiation is of significantly lower energy than the primary beam itself.
ANS: T
DIF: Medium
MULTIPLE CHOICE
1. Which condition is needed to produce an x-ray?
a. a source of electrons
c. a large potential difference
b. a vacuum
d. all of the above
ANS: D
DIF: Medium
2. The function of the cathode is to produce ____.
a. a focal point
c. a thermionic cloud
b. an electrical connection to the rectifier
d. a grounding effect
ANS: C
DIF: Medium
3. Each of the following is a part of the cathode assembly except the ____.
a. filament
c. focusing cup
b. stator
d. associated wiring
ANS: B
DIF: Medium
4. Each of the following is a material of choice for the filament except ____.
a. copper
c. rhenium
b. tungsten
d. molybdenum
ANS: A
DIF: Medium
5. Filament materials are chosen for their ____.
a. low melting points
b. high melting points
ANS: B
c. ability to vaporize easily
d. high boiling points
DIF: Medium
6. Which of the following would affect the production of a thermionic cloud?
a. filament diameter
c. filament temperature
b. filament length
d. all of the above
ANS: D
DIF: Medium
7. A filament may break due to ____.
a. evaporation
b. deposition
c. increased sensitivity
d. vaporization
ANS: D
DIF: Medium
8. Driving the thermionic cloud from the cathode to the anode requires ____.
a. a large potential difference
c. a large amperage
b. a small voltage
d. a small amperage
ANS: D
DIF: Medium
9. Production of the thermionic cloud requires ____.
a. kilovoltage
c. amperage
b. resistance
d. more than one of the above
ANS: D
DIF: Medium
10. The focusing cup has a/an ____ charge.
a. neutral
b. atomic
ANS: D
c. positive
d. negative
DIF: Easy
11. 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 ____.
a. thermionic emission
c. space charge effect
b. biased cloud formation
d. current saturation
ANS: C
DIF: Medium
12. X-ray photon production occurs at the ____.
a. anode
b. cathode
ANS: A
c. filament
d. stator
DIF: Easy
13. Tungsten is the metal of choice for the source of x-ray photons because of its ____.
a. high atomic number
c. low mass number
b. low melting point
d. all of the above
ANS: A
DIF: Easy
14. Pitting of the anode commonly occurs ____.
a. when the unit is not warmed-up properly
b. when the anode is off focus
c. with extended use
d. when the kilovoltage is too high
ANS: C
DIF: Medium
15. Melting of the anode commonly occurs ____.
a. when the unit is not warmed up properly
b. with extended use
c. when the kilovoltage is too high
d. when the stator fails and the rotor ceases to turn
ANS: D
DIF: Medium
16. Cracking of the anode commonly occurs ____.
a. when the kilovoltage is too high
b. when the anode is off focus
c. with extended use
ANS: A
DIF: Medium
17. The exact point in the x-ray unit where photons are created is the ____.
a. focusing cup
c. stator
b. focal spot
d. rotor
ANS: B
DIF: Easy
18. The physical area of the focal track affected by the electron beam is the ____.
a. effective focal spot
c. actual focal spot
b. effective focal track
d. all of the above
ANS: C
DIF: Easy
19. The area of the focal spot that is projected out of the tube towards the object being radiographed is the
____.
a. effective focal spot
c. actual focal spot
b. effective focal track
d. all of the above
ANS: A
DIF: Easy
20. The effective focal spot is controlled by all of the following except the ____.
a. size of the actual focal spot
c. anode target angle
b. length of the filament
d. all of the above
ANS: D
DIF: Medium
21. The actual focal spot is controlled by the ____.
a. size of the actual focal spot
c. anode target angle
b. length of the filament
d. all of the above
ANS: B
DIF: Medium
22. The most common diagnostic radiography target angle is ____ degrees.
a. 12
c. 45
b. 24
d. 54
ANS: A
DIF: Easy
23. As the actual focal spot size increases, the effective focal spot size ____.
a. increases
c. remains the same
b. decreases
d. cannot be determined
ANS: A
DIF: Medium
24. As the angle of the anode increases and the incident electron beam size remains the same, the effective
focal spot size ____.
a. increases
c. remains the same
b. decreases
d. cannot be determined
ANS: A
DIF: Medium
25. To cover a 14 in x 17 ft field at 40 ft, a ____-degree target angle is required.
a. 3
b. 5
ANS: D
c. 7
d. 12
DIF: Medium
26. The use of the line-focus principle causes a problem known as the ____ effect.
a. space charge
c. anode heel
b. quantum mottle
d. vacuum
ANS: C
DIF: Medium
27. The only portion of the anode assembly placed outside the vacuum of the glass envelope is the ____.
a. stator
c. rotating disc
b. rotor
d. molybdenum neck
ANS: A
DIF: Medium
28. The function of the stator and rotor assembly is to ____.
a. create a vacuum
b. rotate the anode
c. insulate the anode
d. disrupt the electromagnets of the induction motor
ANS: B
DIF: Medium
29. The rotor is located ____ the stator and ____ the glass envelope.
a. inside, inside
c. outside, outside
b. inside, outside
d. outside, inside
ANS: A
DIF: Medium
30. The protective housing controls leakage and scatter radiation through ____.
a. evaporation
c. absorption
b. vaporization
d. condensation
ANS: C
DIF: Medium
31. Insulation of the high-voltage components of the tube and absorption of the heat produced by x-ray
production is achieved through the use of ____.
a. a small fan
c. a stator
b. a vacuum
d. dielectric oil
ANS: D
DIF: Medium
32. What type of radiation is composed of photons not produced at the focal spot?
a. off-focus
c. both a and b
b. extrafocal
d. neither a nor b
ANS: C
DIF: Medium
SHORT ANSWER
1. What is the function of the filament?
ANS:
The function of the filament is to provide sufficient resistance to the flow of electrons so the heat
produced will cause thermionic emission to occur.
DIF: Medium
2. List the three functions of the x-ray tube anode.
ANS:
it serves as the target surface for the high-voltage electrons from the filament (x-ray photon source), it
conducts the high voltage from the cathode back into the x-ray generator circuitry, and it serves as the
primary thermal conductor
DIF: Difficult
3. List two other names for the anode target.
ANS:
target, focus, focal point, focal spot, or focal track
DIF: Easy
4. List the three parts of the anode assembly.
ANS:
the anode, the stator, and the rotor
DIF: Medium
5. In which direction should the anode be placed for an AP projection of the femur?
ANS:
Because the inferior upper leg is less dense, the anode’s less intense beam should be positioned toward
the knee to help decrease the film density in that region.
DIF: Medium
6. Why is a vacuum created in the tube?
ANS:
The removal of air permits electrons to flow from cathode to anode without encountering the gas
atoms in the air. This greatly increases the efficiency of the tube’s operation.
DIF: Medium
7. List the three primary functions of the x-ray tube protective housing.
ANS:
The x-ray tube protective housing controls scatter and leakage radiation, isolates the high voltages, and
provides a means to cool the tube.
DIF: Medium
PROBLEM
1. How many heat units are generated by an exposure of 70 kVp, 300 mA, and 0.1 second on a single 
full-wave rectified unit?
ANS:
2,100 HU
DIF: Difficult
2. How many heat units are generated by an exposure of 70 kVp, 400 mA, and 0.1 second on a 3  6pulse unit?
ANS:
3,780 HU
DIF: Difficult
3. How many heat units are generated by an exposure of 100 kVp, 400 mA, and 0.01 second on a 3  12pulse unit?
ANS:
564 HU
DIF: Difficult
4. How many heat units are generated by 3 exposures of 100 kVp, 400 mA, and 0.01 second on a 3  12pulse unit?
ANS:
1,692 HU
DIF: Difficult