physics chapter 5

Question 0

Know what the tube housing is

Answer 0

Lead lined metal structure that serves as an electrical insulator and thermal cushion for the tube itself

Question 1

Where is the X-ray tube situated

Answer 1

In a protective housing

Question 2

Describe the design of the tube housing

Answer 2

Incorporates an oil bath and cooling fans to help dissipate heat away from the tube, protecting it from thermal damage

Question 3

Know why the tube is immersed in an oil bath

Answer 3

Draw heat away from the tube

Question 4

Know the purpose of the cooling fans

Answer 4

Circulate air around the assembly which also helps dissipate heat

Question 5

Know another role of the tube housing

Answer 5

Absorb most of the photons traveling in directions other than toward the patient

Question 6

Define leakage radiation

Answer 6

Photons produced in the X-ray tube that are traveling in directions other than toward the patient

Question 7

What are 2 precautionary things to remember about the tube housing

Answer 7

⚫️with extended on times the housing becomes hot

⚫️the high voltage cables are not handles

Question 8

Describe the general purpose X-ray tube

Answer 8

An electronic vacuum tube that consists of an anode, cathode, and an induction motor all encased in a glass or metal enclosure(envelope)

Question 9

Know the positive and negative ends of the X-ray tube

Answer 9

Anode-positive

Cathode-negative

Question 10

Know what the cathode consists of

Answer 10

Focusing cup and filament with it’s supporting wires

Question 11

Know what the main purpose of the X-ray tube enclosure is

Answer 11

To maintain a vacuum within the tube

Question 12

Be able to describe “sun tanning” of the X-ray tube

Answer 12

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.

Question 13

Know the purpose of the metal envelope

Answer 13

Provides a constant electric potential between the electron stream from the cathode and the enclosure thereby avoiding the arching problem and extending tube life

Question 14

Know why the target window is made of a thinned metal

Answer 14

It reduces the amount of absorption by the enclosure

Question 15

Know what the anode provides

Answer 15

The target for electron interaction to produce X-rays and is an electrical and thermal conductor

Question 16

Know what the purpose of the anode is

Answer 16

Dissipate heat

Question 17

Know the 2 designs of the anode

Answer 17

⚫️stationary anode

⚫️rotating anode

Question 18

Know why it’s called a stationary anode

Answer 18

The target doesn’t move

Question 19

What is the disadvantage of the stationary anode

Answer 19

The electrons always hit the same small target area, heat builds up rapidly and can damage the tube

Question 20

Know which anode is commonly used in today’s xray machines

Answer 20

Rotating anode

Question 21

Know what the rotating anode consist of

Answer 21

A rotating disc made of molybdenum as core material costed with tungsten and mounted on a copper shaft with a molybdenum core

Question 22

Know why cooper is used as part of the shaft on a rotating anode

Answer 22

It has an excellent thermal and electrical conductive properties

Question 23

Know why molybdenum is used as the disc base on a rotating anode

Answer 23

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

Question 24

Know why the target material (coating) is made of tungsten

Answer 24

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

Question 25

Know how the rotating anode is rotated

Answer 25

Using an induction motor

Question 26

Know the two major parts of an induction motor

Answer 26

Stator and rotor

Question 27

Know what the stator is made of

Answer 27

Electromagnets arranged in pairs around the rotor

Question 28

Know what the rotor is made of

Answer 28

Iron core surrounded by coils and located in the center of the stator but within the enclosure

Question 29

Know how the rotor is operated

Answer 29

Mutual induction

Question 30

What is the purpose of the rotating anode

Answer 30

To spread the tremendous heat produced during xray production over a larger surface

Question 31

Know the line focus principle

Answer 31

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

Question 32

Know what the actual focal spot is

Answer 32

Area actually bombarded with filament electrons

Question 33

Know what the effective focal spot is

Answer 33

The xray beam area as seen from the prospective of the patient

Question 34

Know how the effective focal spot will be when the angle of the target is less than 45 degrees

Answer 34

Smaller than the actual

Question 35

Know the range of the target angles for general purpose tubes

Answer 35

7-18

Question 36

Know what the most common angle is for the general purpose tube

Answer 36

12

Question 37

Be able to explain the anode heel effect

Answer 37

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.