xray tube components lecture 1

Cathode Assembly

• filament

• focusing cup

• associated wiring

Cathode assembly function

• controlled source of electrons for x-ray generation (mA)

• acts as the negative electrode

Cathode

• negatively charged

• creates free electrons through thermionic emission

Thermionic Emission

• boiling off of electrons in an electron cloud

• filament is heated

Anode

• absorbs electrons and creates x-rays

• positively charged

Anode assembly

• anode : target disc, focal spot, stem

• rotor : rotor, bearings

• stator : stator windings, support

Anode assembly function

• target surface

• conducts high voltage

• primary thermal conductor

Tube/Glass Envelope

glass (pyrex) or metal vacuum around anode and cathode assembly

window for x-ray exit

Tube Housing

• controls leakage radiation and off-focus radiation

• isolates high voltages

• helps to cool tube

Filament

• thoriated tungsten wire

• most tubes have two focal spot sizes

• sit inside focusing cup or cathode block

wire is heated and results in thermionic emission

10V, 4-5A

focusing cup

'‘focus” the electron beam

negatively charged so it repels the free electrons and presses the back together in a tight electron stream

made of nickel

Anode Disc

typically made of tungsten, onto which the electron beam is focused to generate X-rays.

rotating anode

increases the target area and the heat capacity

Target

where high-energy electrons from the cathode strike, generating X-rays

• A high tension supply, which accelerates the electrons (due to potential difference of VOLTAGE supplied by anode)

Anode Angle

• disc has a beveled edge

• 7-17 degrees

x-ray most commonly use 12 degrees

Electromagnetic Induction Motor

drive the rotating anode

Rotor

• copper cylinder attached directly to anode disc by molybdenum stem

• ball bearings assist with rotation