x-ray tube construction Flashcards
Lead lined structure to absorb non useful x-rays generated at the focal spot
protective housing
_________________ connect to the tube within the housing which acts as an electrical insulator to reduce the risk of shock
Two large electrical cables
Radiation that is produced in directions other than the target window and escapes the protective housing is referred to as ________________
leakage radiation
Protective housing MUST reduce leakage radiation to less than __________
100 mR/hr
housing helps cool x-ray tube in 2 ways
- forced air cooling
- oil
anode is ______, cathode is _________
positive, negative
two main components of the x-ray induction motor
stator (fixed), rotor (rotating)
a rotating anode makes a focal spot a _________
focal tract
the maximum stress load that a material can take before breaking
tensile strength
Steeper angles of the target create __________________________ which then increases the sharpness of the image and allows smaller structures to be visualized in the radiograph
smaller effective focal spot sizes
Steeper angles of the target create smaller effective focal spot sizes which then ___________________ and _______________________
increases the sharpness of the image, allows smaller structures to be visualized in the radiograph
what is the actual focal spot?
the area of the target that is being struck by the filament electrons
what is the effective focal spot?
the x-ray beam area as seen from the patient’s perspective
As long as the target angle is less than ____°, the effective focal spot will always be smaller than the actual focal spot
45 degrees
Generally, the target angle is between ____° with the average being around __°
7-18, 12
A small filament will create a (larger/smaller) actual focal spot which will then create a (larger/smaller) effective focal spot
smaller, smaller
The smaller the effective focal spot, the _____________________. Therefore, it is necessary to _______________________
sharper the image will be; keep this as small as practically possible
two drawbacks to line focus principle
- if angle of target is too small, it may not be big enough for 14x17 field at 40 SID
- the angle causes the intensity of the x-ray beam to be less on the anode side (anode heel)
If the center of the beam was 100% of the intensity, then the anode side would average as low as ___% of that intensity and the cathode side would have ___%
75%, 120%
Rotating anodes are made of tungsten as well and for the same reasons although other materials such as _________
Rhenium
Rhenium may be added to increase __________ as well as ____________
thermal capabilities as well as tensile strength
The rotating disc is made of ______________ and is covered with the ________________________ and is connected to a molybdenum core within a copper shaft
Molybdenum, target material (tungsten or tungsten/molybdenum)
The rotating disc is made of Molybdenum and is covered with the target material (tungsten or tungsten/molybdenum) and is connected to a _________________________
molybdenum core within a copper shaft
Molybdenum is used as a base for the disc and core because of its _________________ and __________________
light weight which makes it easier to rotate and its incredible ability to dissipate heat
Filaments are usually between _________ in length and ________ wide
7-15 mm, 1-2 mm
Filaments are made of tungsten with _____________________ added to increase thermionic emission and tube life
1-2% thorium
why is thorium added to the tungsten filament?
increase thermionic emission and tube life
what is the focusing cup made of?
nickel
effectiveness of the focusing cup depends on several things
- The size and shape of the cup
- .The charged placed on the cup
- The size and shape of the filaments within the cup
- The position of the filaments within the cup
the size of the effective focal spot ___________ as the target angle decreases
decreases
One half of the range between the wave peak and valley over which the sine waves varies describes
amplitude
