X-ray tube/Cathode Flashcards
What is the charge on the cathode side?
negative
What does the cathode house?
large and small filaments
focusing cup
The cathode is the site of…
electron production
What is applied to the focusing cup to achieve a negative charge? During when?
low negative potential
during electron production
What is applied to the cathode end of the tube during an exposure?
large negative potential
What is the focusing cup made of? Why?
nickel
its high heat capacity
The focusing cup houses what?
the 2 (large and small) filaments
What does the focusing cup do?
helps accelerate electrons toward the anode
During what process do the focuses produce electrons?
thermionic emission
Thermionic emission
the boiling off of electrons due to the heating of the small coil of thoriated tungsten wire (electron cloud)
List 2 reasons why Tungsten is an ideal target material.
high melting point (6192 degree F)
high Z number (74)
Why are the tungsten filaments coated in Thorium?
it’ll burn off about 2% more electrons, resulting in a more efficient thermionic emission process
what do electrons form when the Tungsten filament is heated up?
“thermionic cloud”
“space charge”
What is the most common type of x-ray tube failure
tungsten filament vaporization
most x-ray tubes are considered to be what?
dual focus (2 filaments)
What is the small focal spot used for?
greater spatial resolution and smaller body parts
What is the large focal spot used for?
larger body parts (requires more electrons)
What is the principal advantage of using the large filament?
increased heat capacity
What can the electrons of the large focal spot be turned into?
x-ray photons
What is the x-ray tube made of and why?
Pyrex glass to enable it to withstand the heat generated
The x-ray tube is __________ to the heat produced by the heating of the filament and the electron interaction with the anode.
resistant
In what way do electrons travel to the anode?
unimpeded (freely)
What helps dissipate the heat generated during x-ray production in the tube?
oil bath
What process does the surrounding of the oil bath help aid?
convection
What makes a gassy tube?
electrons strike the heat residue of tube, creating a gassy substance
no longer a vacuum tube
What things are needed to efficiently produce x-rays?
- source of electrons
- acceleration of electrons
- a vacuum
- a target
What is a space charge?
cloud of free electrons made from Tungsten filament heating up
The space charge affect limits the mA of the x-ray tube to approximately:
1000 mA
