X-ray tube components Flashcards
(38 cards)
What is the envelope made of
pyrex glass or metal
what is the purpose of the envelope
maintain a vacuum between the cathode and anode, protects inner parts
*why vacuum?
-photons and electrons travel w/o interacting w/ air (keeps X-ray precise)
What are the benefits of a metal envelope instead of glass
less likely to break
tube is grounded
better conductibility
What is the protective housing made of
Lead (on cathode end)
Steel
*why?
-helps reduce heat & leakage radiation
what is the purpose of the protective housing
controls leakage radiation
*any radiation coming out of tube somewhere other than the window
what is the maximum limit of leakage radiation
100 mR (milliRoentgen) per hour or
1 milligray per hour
What is the high-voltage isolation & tube cooling system made of
Dielectric oil
Air fan
what is the purpose of the high-voltage isolation & tube cooling system
Reduce heat and shock
helps cool tube
What is the filament made of
coil of thoriated tungsten
*why?
-high melting point
-does not vaporize easily
Note: rhenium and molybdenum are also good choices
is the filament on the cathode or anode end of the tube
Cathode (-)
what is the purpose of the filament
produce negative charge by boiling off electrons
*this is thermionic emission
why does filament size (length/width) matter
This is picked via focal spot
-impacts recorded detail
what kind of detail does a longer filament (Large focal Spot) have
Less (worse) detail
what kind of detail does a shorter filament (small focal spot) have
More (better) detail
what are the dimensions of the filament coil
0.1-0.2 mm thick
1-2 mm wide
10-20 mm long
what is the focusing cup made of
Nickel
*negative potential applied to narrow (concentrate) cloud of electrons
what is the purpose of the focusing cup
concentrates electron beam towards focal track of the anode
Also holds filament
what is a biased focusing cup
has higher negative potential, so cloud of electrons is narrowed even more
what is the space charge effect
cloud of electrons gets so large; it stops more electrons from being boiled off of filament
is the focusing part located within the cathode or anode side of the tube
Cathode (-)
what is the focal track made of
where electrons strike it is made of tungsten-rhenium alloy
*why?
-thermal conductivity
-high melting point
-high atomic #
(more electrons available for more interactions to occur)
what is the back/base of the anode made of
Molybdenum and/or graphite
*why?
-lighter material allows for easier rotation
-high conductibility
-thermal dissipation
What is the purpose of the anode
It is the target surface where electrons get projected off X-ray photons are created
Electrical conductor
-taking electron source & heat then putting it back in circuitry
Thermal dissipator
-prevents overheating
what is actual focal spot
where electrons strike the rotating anode
