RAD 111 Unit 3 x-ray tube

A x-ray tube has an

anode and cathode

Anode charge?

positive

Cathode charge?

negative

X-ray production requires

an electron stream that is decelerated/stopped

The cathode is a source of what?

electrons/negatively charged

The anode is the location of

rapid deceleration/positvely charges

What creates X-rays and heat?

Rapid deceleration

What is a cathode filament mostly made of?

tungsten, similar to lightbulb

Cathode purpose

thermionic emission

Thermionic emission

filament boost

The release of electrons from the tungsten filament when the electrical current passes through it and heats the filament

Thermionic emission creates

thermionic cloud/space charge or electron cloud

Space charge

A cloud of electrons formed by the focusing cup as electrons are boiled off of the filament.

Cathode dual focus

2 filaments: Small and Large filaments

Cathode: Small Filament

Low mA

Small body parts

Cathode: Big Filament

High mA

Big body parts

Cathode: The focusing cup is mainly made up of what?

nickel

Cathode: focusing cup causes

Electrostatic repulsion

Cathode: Electrostatic repulsion

keeps the electrons together

Anode is mainly made up of what?

molybdenum coated with tungsten (90% is tungsten). Also, may have copper, and graphite in the anode.

Anode acts as a

low thermal conductivity

Low thermal conductivity does what?

slows the migration of heat to the rotor

Anodes function/targets

decelerates electrons

opposite charge

Anode is a

Thermal conductor

Thermal conductor

conducts heat away from the focal spot

Anode: target/focal spot/focal track location

where the electron stream strikes the anode

Anode: target/focal spot/focal track main material

Tungsten, due to its high atomic # and high melting point

Anode: target/focal spot/focal track second material

Rhenium alloy due to its ability to hold tungsten particles together under high heat

What is tungsten's melting point?

3400 °C or 6152° F

Types of Anodes

stationary and rotating

Stationary anodes are used for what?

dental units

Rotating anodes are used for what?

diagnostic

Rotating anodes rotate at what RPMs?

3000-10,000 rpms, needed for heat dispersion

What is the rotating anode angles?

5-20°

Rotating anodes function?

Dissipates heat

Rotating anode: Stator

made of electromagnets located outside the glass tube

Stator function

The electric motor turns the rotor at high speeds

Rotating anode: Rotor

connected to the target through the anode stem

Rotating anode: Ball Bearings

allow free rotation of the rotor

Rotating anode: Rotor + stator + Bearings =

induction motor

Rotating anode: Dielectric Insulating oil

surrounds the tube

Dielectric Insulating oil function

-Additional layer of insulation

-Pulls heat away from the tube

Rotating anode: Fan

blows air over the tube

Tube Housing

Glass envelope

Protective housing

Glass envelope

Pyrex glass or metal envelope

Glass envelope function

-Vacuum allows electrons to travel without encountering air atoms ◦

-This allows the filament to heat up without burning

-Insulates the high voltage (tech will not get shocked)

-Dissipates heat away from tube components

Protective housing materials

Steel lined with lead

Protective housing function

-Absorbs all photons except those directed towards the patient

-Leakage radiation not to exceed 100mR/hr (1 mGya/hour) @ 1 meter using maximum Kv and MaS

What is 1?

Rotating anode

What is 2?

Tungsten target

What is 3?

Stator

What is 12?

Rotor

What is 4?

Ball races

What is 10?

+100,000 V

What is 5?

Anode stem

What is 6?

X-ray

What is 7?

Electron beam

What is 8?

Hot cathode filament

What is 9?

0 V

What is 11?

6.3 V ac