Anode

List the 4 functions of the anode assembly

1. serves as the target surface for the high-speed electrons from the cathode

2. the source of the x-ray photons

3. conducts the high voltage from the cathode

4. serves as the primary thermal conductor

What are the two types of anodes?

1. stationary

2. rotating

What type of anode is a block of tungsten imbedded in the 45 degree angled end of a copper rod?

 stationary anode

A stationary anode is about how much surface area and where is it found?

about 1.5 cm x 1 cm

only found in dental equipment and old x-ray units

Which anode type provides a greater surface area?

rotating anode

Which anode type dissipates heat better?

rotating anode

________ anode = 4mm² (surface area)

________ anode = 1835 mm²

stationary

rotating

What anode is used in most modern x-ray units?

rotating anode

What is the composition of the rotating anode disk?

• 5 to 13 cm in diameter

• made of molybdenum

What is the composition of the target focal track (rotating anode)?

tungsten-rhenium alloy

What is the composition of the anode disk backing (rotating anode)?

molybdenum or graphite

List 3 advantages of tungsten as target material

1. high melting point (tungsten = 3370 C)

2. high atomic number (tungsten = 74)

3. heat-conducting ability

What is the area of electron interaction called? (what else is it called?)

the target area (focus, focal point, focal spot, or focal track)

What is the area where x-rays are created?

the target area

The _______ focal spot is the physical area of the focal track that is impacted by the electrons.

actual

The _______ focal spot is the area of the focal spot that is projected out of tube toward the patient.

effective

What is the effective focal spot controlled by?

the size of the actual focal spot (length of the filament) and the anode target angle

(Line Focus Principle)

When the target is angled (less than 45 degrees) the effective focal spot is _____ than the actual focal spot.

smaller

The smaller the angle, the _____ the effective focal spot.

smaller

What do anode angles range from?

What is the most common?

7 to 17 degrees

12 degrees

Because of the geometry of the angled anode target, the radiation intensity is greater on the ______ side.

cathode

How much can the intensity of the x-ray beam vary from anode to cathode?

45%

What is outside the glass envelope and consist of series of electromagnets that rotate the rotor?

stator

What is inside the glass envelope that revolves at 3,400 RPM?

rotor

A high speed rotor revolves at _____ RPM.

10,000