Day 2 Questions Flashcards
Give three things needed to produce X-Rays
1) A plentiful supply of free electrons supplied by a filament
2) A means of accelerating them in a given direction at high velocity
3) Available atoms from a dense substance (high atomic weight) against which the stream of electrons will impact
Why is the Target (X-Ray tube) made of Tungsten?
1) High atomic number
2) Thermal conductivity
3) High melting point 3380c
4) Low Vapour pressure
Why is a Filament (X-Ray Tube) made of Thoriated Tungsten?
1) Thorium helps emission
2) Tungsten undergoes thermionic emission better than most other metals
3) Tungsten has a high melting point (3380c)
4) Tungsten will not vaporize easily - gases in the tube cause electrical imbalances and tube failure
Why is the Anode (X-Ray Tube) made of copper?
1) An electrical conductor for the impacting electrons
2) A Mechanical support for the target
3) A thermal conductor
Explain the Focus Line Principle
The “Actual Focus Spot” is the area where the electrons impact on the target. This has to be as large as possible to avoid local overheating, but the resulting useful x-ray beam has to be small as possible to achieve maximum image sharpness. Both aims are achieved by angling the anode at approximately 20 degrees to the centre of the free electron beam.
Explain the importance of Duty Cycle (X-Ray Tube)
This will extend the life of the main components of the tube.
Allows the components to cool.
Explain Quantity (Intensity) of X-Rays
Refers to the number of X-Rays being produced.
The amount of X-Rays emitted is directly proportional to the tube current.
Example: if the tube current is doubled, then the amount of X-Rays is doubled
Explain Quality (Penetrating) X-Rays
The harder the electrons accelerate, the faster they will be moving when hit they hit the target.
The faster they are moving, the more energy they will have. This greater energy will be given off as short X-Rays which has greater penetrating ability.
Lower energy = longer wavelengths= less penetrating
What is the Cathode (X-Ray Tube)
The main body is generally made out of nickel or iron.
The Filament is located inside the Focussing Cup, which is recessed into the Cathode.
What is Thermionic Emission?
When passing current through the filament and heat it to incandescence.
Electrons are then “boiled off” the filament surface. This is known as Thermionic Emission
What is the Anode (X-Ray Tube)
The anode is considered the positive side the tube because of the high electrical charge applied to it. The potential difference this charge and the filament accelerates the electrons to high speed.
The Hood (X-Ray Tube)
Located in the Anode
Helps to eliminate a portion of the X-Ray beam outside the cone of radiation.
Manufactured from copper, can help reduce the amount of shielding that must be provided externally or incorporated into the tube housing.
What is Kilovoltage (X-Ray Tube)
The potential difference between the Anode and the Cathode provides the accelerating force on the electrons
Both Anode and Cathode are charged by a electric current
Quality or Penetrating Ability
What’s is milliamperage (ma) control?
The way to increase/decrease the number of electrons/X-rays being produced.
Quantity or Intensity
What is the Importance of Warm Up Cycle?
Burn off oxides on wire
Prevent backfiring
