Tube rating charts Flashcards
Name the external components of an x-ray tube
- Ceiling Support system
- Floor to ceiling support system
- C-arm support system
- Protective housing
- Glass/metal enclosure
Which x-ray unit is most common
The ceiling support system
Leakage radiation must be no more than ____>
1 mGy/hr @ 1 meter from the source
What is the purpose of protective housing
guards against excessive radiation exposure & electric shock
What is the tube ( anode & cathode) enclosed by?
Glass vacuum
What surrounds the glass vacuum x-ray tube
metal housing
What happens when the area inside the glass tube housing is not a vacuum?
the electrons collide with other atoms when traveling from the cathode to the anode and thus, creates less x-rays or lower energy xrays, AND decreases the efficiency of the tube.
What are the internal components of the x-ray tube
Cathode and Anode
Where does thermionic emission take place
in the cathode side of the tube
What does the cathode consists of
- negative side of tube*
Contains:
-Filaments
-Focusing cup
What is the positive side of the x-ray tube
anode
What are the 2 types of anodes
- Rotating
(used in x-ray)
2.Stationary
(used in dental)
Why are rotating anodes used in general x-ray
because they can produce high intensity x-ray beam in a short amount of time
What is the anode made of
- Tungsten
- Molybdenum
- Rhodium
Why is tungsten used in the anode
- High atomic #
- Thermal conductivity
- High melting point
What is the element for:
- Tungsten
- Molybdenum
- Rhodium
- W
- Mo
- Rh
Fixed electromagnets of the tube are called
Stators
What is the purpose induction motor of anode
It is an electric motor where magnetic field is supplied to fixed electromagnets called stators to rotate the rotor of the anode
Electric motor where magnetic field is supplied to fixed electromagnets called stators to rotate the rotor of the anode
Induction motor of anode
What is the line focus principal
A designed added to x-ray tube targets that allow for larger heating areas while a small focal spot is maintained
How is focal spot size controlled
Controlled by angle of the target
Effective focal spot size is _____ than the actual spot size
less than the actual spot size
The larger the target angle the ____ focal spot size
larger
How does a change in focal spot affect the anode
the tube changes the location of the anode
small= towards center of anode
Large= edge of anode
What is an undesirable result of line focus principal
unequal radiation intensity across the anode & the cathode
Intensity is greater on the ___ side, as a result of electrons hitting the target at different depths
Cathode
The ___________ the anode angle, the larger the heel effect
smaller
What are some of the things we use to reduce the anode heel-effect
Filters
What are 3 ways that heat is dissipated from the x-ray tube
- Radiation
- Conduction
- Convection
The transfer of heat by the emission of infrared radiation is _____
Radiation
The transfer of energy from one area of an object to another is _____
Conduction
The transfer of heat by a movement of a heated substance from one place to another
Convection
Excessive heat results in ____
reduced x-ray tube life
What do we do as technologists to prolong tube life?
Tube warm up
Name factors that prolong tube life
- Tube warm up
- Low techniques
- Faster IR’s/screens
Maximum radiographic techniques should never be applied to a cold anode. Why?
anode pitting occurs
= this means that the tungsten removed during pitting get deposited in the glass envelope of tube housing
which causes tube arching
What are the 3 types of tube failure
- excessive heat during single exposure
- maintaining anode at elevated temperatures
- Filament
What does excessive heat during exposure cause?
causes anode to crack which is then unstable during rotation
Name the 3 types of rating charts
- Radiographic` tube rating charts
- Anode cooling chart
- Housing cooling chart
Which rating chart is most important and why
Radiographic rating chart because it details which techniques are safe to use and which are not for tube operation
Phase refers to what type of generator the tube is powered by….
What are some types of generators?
single phase three phase high frequency half wave full wave
Large effective focal spot has which anode angle?
Large
How is thermal energy in x-ray applications measured in
Heat Units (HU)
or
Joules (J)
The capacity of the anode and the housing to store heat is measured in ___?
HU
Heat units
1 heat unit is equal to
___ kVp
___mA
___ s
1 kVp
1 mA
1 s
How would you find a HU for single phase
kVp x mA x time
How would you find HU for High frequency circuit
kVp x mA x time x 1.4
The ____ will overheat long before the tube housing will
anode
Why does the anode overheat before the tube housing?
- the anode is being directly bombarded with electrons, where the tube housing is indirectly bombarded
AND - the anode is made of tungsten where the tube housing is made of an insulator material)
