Chapter 5 Flashcards
What is the tube housing usually made from?
Metal with a lining of lead
What kind of radiation does the tube housing protect from?
Leakage radiation
How much leakage radiation is allowable from the tube?
1 mGy/hr at 1 meter
Where are x-rays made?
The actual focal spot
What is isotropic?
X-rays go everywhere with high intensity in all directions
What is inside the x-ray tube?
Anode and cathode
What is the function of di-electric oil?
Located outside of tube for heat distribution absorption
What can cause tube arc or failure?
Tube gasification from the tungsten filament
What is the useful beam?
Where xrays come from the tube window out onto the patient
What are the primary parts of the cathode?
Filament (large and small)
Focusing cup
Filament wires
What is filament made of?
Thoriated Tungsten
What is the high melting point of tungsten?
3400 degrees celcius
6152 degrees F
What is saturation current?
Filament emits electrons when heated, to the point it can’t produce anymore electrons
What is thermionic emission?
Electons are boiled off
What charge does filament carry?
Negative
Where do electrons hang out in the focusing cup?
Space charge (electron cloud)
What is the anode made of?
Target - tungsten (w/ rhenium)
Neck and base - molybdenum or graphite
How does the anode rotate?
Induction motor
Why is a rotating anode better than stationary?
Good thermal dissipater
Gets rid of heat
Allows for more tungsten to be hit by electrons
What 4 things are needed to produce xrays?
- Source of free electrons
- Means to accelerate them (kVp)
- Decelerate them (tungsten)
- Angle them down - actual focal spot
What is atomic number for Tungsten?
74
What is the Line Focus Princple?
Anode has different angles for small and large focal spot sizes.
What is the relationship between anode angle size and heel affect?
Smaller the angle, the greater heel effect
(more electrons get caught in heel of focal point)
What is the relationship between the anode angle and spatial resolution?
The smaller the angle, the better the spatial resolution
What is the equation for heat load capacity?
kVp x mAs x c x # of exposures
How does inherent filtration affect beam?
Makes beam stronger by eliminating weak photons
What are the generator correction factors?
Single phase - 1.0
Three phase, 6 pulse - 1.35
Three phase, 12 pulse - 1.41
High frequency - 1.45
What are the 3 types of heat produced?
Radiation
Conduction
Convention
