7. X-RAYS: TUBE INSERT

Question 1

1. What is this image showing?

Answer 1

• the insert
• this is found inside the X-RAy Tube

Question 2

2. Provide the labels for the parts numbered 1-6.

Answer 2

1. Cathode Assembly
2. Vacuum
3. Anode Disk
   (the electrons travel towards the Anode)
4. Anode Stem
5. Rotor
6. HT Connection

Question 3

3. Provide the labels for the parts numbered 7-12.

Answer 3

7. HT Cable
8. Rotor Support
9. Bearings
10. Focal Track
11. Filament
    (set in focusing)
12. Glass Envelope

Question 4

4. What does the Insert maintain?

Answer 4

• it maintains a vacuum for the X-Ray Production

Question 5

5. What does the Insert contain?

Answer 5

• the Anode Assembly
• the Cathode Assembly

Question 6

6. What happens to the Metal Component of the Insert?

Answer 6

• it is Earthed
• this is so that there is no build up of static

Question 7

7. What fixes the anode and the cathode assembly to the Insert?

Answer 7

• the envelope
• it supports the two electrodes
• it keeps them at the correct distance away from each
  other
• it aligns them correctly

Question 8

8. How are the seals and the metal poles chosen?

Answer 8

• they are chosen carefully
• this is to match the expansion coefficients (heat) of the
  different parts
• this reduces the risk of damage to the insert during the
  Operation

Question 9

9. What do these images show?

Answer 9

• The Anode Assembly

Question 10

10. What does the Anode Assembly consist of?

Answer 10

1. the Anode Disc
2. the Focal Track
3. the Rotor Assembly
4. the HT Connection for the positive side of the Tube
   Circuit

Question 11

11. What materials make up the Rotating Anode?

Answer 11

• a Tungsten Rhenium Disc
• this typically is 90-150mm in diameter
• this makes this a large rotating disc
• this increases the tube rating and the thermal capacity

Question 12

12. What can be said about the content of the Anode Disc?

Answer 12

• it may be a composite disc
• it has either a Tungsten or a Rhenium focal track
• it has either a Graphite or Molybdenum backing
• it has bevelled edges
• these form the Anode Angle and the Focal Track

Question 13

13. Why does the Anode Angle exist?

Answer 13

• it decreases the size of the apparent focal spot

AN INCREASE IN THE ANODE ANGLE:
- increases the size of the focal spot
- this increases the heat capacity

Question 14

14. What is the Typical Angle for the rotating X-Ray tubes?

Answer 14

• between 16° and 20°
• this produces a better quality of the image
• this results in better spatial resolution

Question 15

15. What is the Anode attached to?

Answer 15

• the Molybdenum Stem
• this connects it to the rotors

Question 16

16. What can be said about the contents of the Anode Stem?

Answer 16

• it has a small cross-section
• the anode stem is as long as possible
• it is connected to the Copper Rotor Assembly

Question 17

17. Why is the Anode Stem as long as it can possibly be?

Answer 17

• this restricts the conduction of heat to the bearing
  assembly

Question 18

18. What do the Rotors do to the Anode?

Answer 18

• they rotate the Anode at speeds of 3000-9000 r.p.m
  during exposures
• they do this using induction

Question 19

19. What is this image showing?

Answer 19

• the Cathode Assembly
• this is negatively charged

Question 20

20. Write down the labels for the parts numbered 1-3.

Answer 20

1. Focusing Cup
2. Wire Filament for the Small Focal Spot
3. Wire Filament for the Large Focal Spot

Question 21

21. Does this diagram make sense?

Answer 21

• yes

Question 22

22. What does the Cathode Assembly consist of?

Answer 22

1. the Filaments
   (fine and broad)
2. the Focusing Cup
   (this is negatively charged)
3. Electrical supplies and Connections

Question 23

23. What are the Electrical Supplies and Connections related to the Cathode Assembly?

Answer 23

1. The Filament Supply
   
   • this is the current
   • it defines the intensity of the X-Ray Beam
   • it defines the number of Photons and Electrons in the
     X-Ray beam
2. The HT Supply
   
   • to the negative side of the X-Ray Tube Circuit
   • this is the voltage supply
   • it is connected to the Cathode

Question 24

24. What is the purpose of the Cathode?

Answer 24

• to produce a thermionic emission of electrons
• these can be focused
• they can be attracted to the anode

Question 25

25. How is Thermionic Emission achieved?

Answer 25

- it is achieved by supplying a variable (mA/current) - this heats up the filament

Question 26

26. How is the filament positioned?

Answer 26

- it is tightly coiled

Question 27

27. What does an increase in the mA (current) result in?

Answer 27

- an increase in the temperatures of the filament - this increases the number of electrons in the electron cloud

Question 28

28. What is the mathematical relationship between the current and the number of electrons?

Answer 28

- mA (current) is directly proportional to the number of X-Rays produced ∴ DOUBLING THE CURRENT (mA) FROM 100 TO 200: - double the number of electrons

Question 29

29. What is the Filament of the Cathode Focusing Cup encased in?

Answer 29

- it is encased in a Nickel Housing (this can also be stainless steel in some occasions)

Question 30

30. What is the function of the Filament's Nickel Housing?

Answer 30

- it focuses the electrons on to the focal track of the anode - this is achieved by it have sharp edges to the Focusing Cup - these edges become negatively charged when the tube voltage is applied

Question 31

31. What does the sharp edge of the Nickel Housing of the filament do?

Answer 31

- it concentrates the negative charge - it narrows the electron beam directly towards the anode