physics chapter 5 Flashcards Preview

spring 2015 > physics chapter 5 > Flashcards

Flashcards in physics chapter 5 Deck (38)
Loading flashcards...
0
Q
Where is the X-ray tube situated
A
In a protective housing
1
Q
Know what the tube housing is
A
Lead lined metal structure that serves as an electrical insulator and thermal cushion for the tube itself
2
Q
Describe the design of the tube housing
A
Incorporates an oil bath and cooling fans to help dissipate heat away from the tube, protecting it from thermal damage
3
Q
Know why the tube is immersed in an oil bath
A
Draw heat away from the tube
4
Q
Know the purpose of the cooling fans
A
Circulate air around the assembly which also helps dissipate heat
5
Q
Know another role of the tube housing
A
Absorb most of the photons traveling in directions other than toward the patient
6
Q
Define leakage radiation
A
Photons produced in the X-ray tube that are traveling in directions other than toward the patient
7
Q
What are 2 precautionary things to remember about the tube housing
A
⚫️with extended on times the housing becomes hot
⚫️the high voltage cables are not handles
8
Q
Describe the general purpose X-ray tube
A
An electronic vacuum tube that consists of an anode, cathode, and an induction motor all encased in a glass or metal enclosure(envelope)
9
Q
Know the positive and negative ends of the X-ray tube
A
Anode-positive
Cathode-negative
10
Q
Know what the cathode consists of
A
Focusing cup and filament with it's supporting wires
11
Q
Know what the main purpose of the X-ray tube enclosure is
A
To maintain a vacuum within the tube
12
Q
Be able to describe "sun tanning" of the X-ray tube
A
As the tube age vaporized transfer from the filament deposits on the inside of glass causing bronze discoloration of the glass. This causes problems with arching and damage.
13
Q
Know the purpose of the metal envelope
A
Provides a constant electric potential between the electron stream from the cathode and the enclosure thereby avoiding the arching problem and extending tube life
14
Q
Know why the target window is made of a thinned metal
A
It reduces the amount of absorption by the enclosure
15
Q
Know what the anode provides
A
The target for electron interaction to produce X-rays and is an electrical and thermal conductor
16
Q
Know what the purpose of the anode is
A
Dissipate heat
17
Q
Know the 2 designs of the anode
A
⚫️stationary anode
⚫️rotating anode
18
Q
Know why it's called a stationary anode
A
The target doesn't move
19
Q
What is the disadvantage of the stationary anode
A
The electrons always hit the same small target area, heat builds up rapidly and can damage the tube
20
Q
Know which anode is commonly used in today's xray machines
A
Rotating anode
21
Q
Know what the rotating anode consist of
A
A rotating disc made of molybdenum as core material costed with tungsten and mounted on a copper shaft with a molybdenum core
22
Q
Know why cooper is used as part of the shaft on a rotating anode
A
It has an excellent thermal and electrical conductive properties
23
Q
Know why molybdenum is used as the disc base on a rotating anode
A
It has a low thermal conductivity which slows migration of heat into the rotor bearings (minimizing heat damage) and it is light but strong making it easier to rotate the anode
24
Q
Know why the target material (coating) is made of tungsten
A
It has a very high melting point (3400 degrees C and 6152 degrees F) and it's thermal conductivity is almost equal to that of copper
➡️has a high atomic number improving efficiency of xray production
25
Q
Know how the rotating anode is rotated
A
Using an induction motor
26
Q
Know the two major parts of an induction motor
A
Stator and rotor
27
Q
Know what the stator is made of
A
Electromagnets arranged in pairs around the rotor
28
Q
Know what the rotor is made of
A
Iron core surrounded by coils and located in the center of the stator but within the enclosure
29
Q
Know how the rotor is operated
A
Mutual induction
30
Q
What is the purpose of the rotating anode
A
To spread the tremendous heat produced during xray production over a larger surface
31
Q
Know the line focus principle
A
States that by angling the face of the anode target a large actual focal spot size can be maintained and a small effective focal spot size can be created
32
Q
Know what the actual focal spot is
A
Area actually bombarded with filament electrons
33
Q
Know what the effective focal spot is
A
The xray beam area as seen from the prospective of the patient
34
Q
Know how the effective focal spot will be when the angle of the target is less than 45 degrees
A
Smaller than the actual
35
Q
Know the range of the target angles for general purpose tubes
A
7-18
36
Q
Know what the most common angle is for the general purpose tube
A
12
37
Q
Be able to explain the anode heel effect
A
The angle causes the intensity of the xray beam to be less on the anode side because the "heel" of the target in in the path of the beam. Meaning, that the X-rays on the anode side must first penetrate a portion of the target before exiting the tube. Some do not have the energy to do so and are absorbed in the target heel, reducing the intensity on the anode side.