7. X-RAYS: TUBE INSERT Flashcards
1
Q
- What is this image showing?
A
- the insert
- this is found inside the X-RAy Tube
2
Q
- Provide the labels for the parts numbered 1-6.
A
- Cathode Assembly
- Vacuum
- Anode Disk
(the electrons travel towards the Anode) - Anode Stem
- Rotor
- HT Connection
3
Q
- Provide the labels for the parts numbered 7-12.
A
- HT Cable
- Rotor Support
- Bearings
- Focal Track
- Filament
(set in focusing) - Glass Envelope
4
Q
- What does the Insert maintain?
A
- it maintains a vacuum for the X-Ray Production
5
Q
- What does the Insert contain?
A
- the Anode Assembly
- the Cathode Assembly
6
Q
- What happens to the Metal Component of the Insert?
A
- it is Earthed
- this is so that there is no build up of static
7
Q
- What fixes the anode and the cathode assembly to the Insert?
A
- the envelope
- it supports the two electrodes
- it keeps them at the correct distance away from each
other - it aligns them correctly
8
Q
- How are the seals and the metal poles chosen?
A
- 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
9
Q
- What do these images show?
A
- The Anode Assembly
10
Q
- What does the Anode Assembly consist of?
A
- the Anode Disc
- the Focal Track
- the Rotor Assembly
- the HT Connection for the positive side of the Tube
Circuit
11
Q
- What materials make up the Rotating Anode?
A
- 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
12
Q
- What can be said about the content of the Anode Disc?
A
- 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
13
Q
- Why does the Anode Angle exist?
A
- 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
14
Q
- What is the Typical Angle for the rotating X-Ray tubes?
A
- between 16° and 20°
- this produces a better quality of the image
- this results in better spatial resolution
15
Q
- What is the Anode attached to?
A
- the Molybdenum Stem
- this connects it to the rotors
16
Q
- What can be said about the contents of the Anode Stem?
A
- it has a small cross-section
- the anode stem is as long as possible
- it is connected to the Copper Rotor Assembly
17
Q
- Why is the Anode Stem as long as it can possibly be?
A
- this restricts the conduction of heat to the bearing
assembly
18
Q
- What do the Rotors do to the Anode?
A
- they rotate the Anode at speeds of 3000-9000 r.p.m
during exposures - they do this using induction
19
Q
- What is this image showing?
A
- the Cathode Assembly
- this is negatively charged
20
Q
- Write down the labels for the parts numbered 1-3.
A
- Focusing Cup
- Wire Filament for the Small Focal Spot
- Wire Filament for the Large Focal Spot
21
Q
- Does this diagram make sense?
A
- yes
22
Q
- What does the Cathode Assembly consist of?
A
- the Filaments
(fine and broad) - the Focusing Cup
(this is negatively charged) - Electrical supplies and Connections
23
Q
- What are the Electrical Supplies and Connections related to the Cathode Assembly?
A
- 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
- The HT Supply
- to the negative side of the X-Ray Tube Circuit
- this is the voltage supply
- it is connected to the Cathode
24
Q
- What is the purpose of the Cathode?
A
- to produce a thermionic emission of electrons
- these can be focused
- they can be attracted to the anode
25
Q
- How is Thermionic Emission achieved?
A
- it is achieved by supplying a variable (mA/current)
- this heats up the filament
26
Q
- How is the filament positioned?
A
- it is tightly coiled
27
Q
- What does an increase in the mA (current) result in?
A
- an increase in the temperatures of the filament
- this increases the number of electrons in the electron
cloud
28
Q
- What is the mathematical relationship between the current and the number of electrons?
A
- 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
29
Q
- What is the Filament of the Cathode Focusing Cup encased in?
A
- it is encased in a Nickel Housing
(this can also be stainless steel in some occasions)
30
Q
- What is the function of the Filament’s Nickel Housing?
A
- 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
31
Q
- What does the sharp edge of the Nickel Housing of the filament do?
A
- it concentrates the negative charge
- it narrows the electron beam directly towards the
anode
