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RAD SCI Unit II
x-ray tube ch. 5
| Term | Definition |
|---|---|
| isotropic | in all directions |
| leakage radiation | any photons that escape from the housing except at the port |
| cathode | source of electrons; negatively charged |
| anode | includes target where x-rays are produced; positively charged |
| focusing cup | focuses electrons to anode and surrounds the cathode filaments; made of nickel |
| tungsten | atomic number of 74; high melting point; low vaporization |
| smalll filament | filament; better for imaging small parts; better resolution |
| large filament | filament; better for imaging large parts or situations that need short exposure time |
| thermionic emission | when tungsten filament gains enough heat, outer shell electrons of filament atoms are boiled off and ejected from filament |
| space charge | electrons boil off and gather in a cloud around the filament |
| target/focal spot | the portion of the anode that is impacted by the high-voltage electron stream |
| line focus principle | the size of the effective focal spot is less than the size of the actual focus spot |
| 12 degrees | the most common anode angle |
| lesser; smaller | _____ angle create a _____ effective focal spot |
| anode heel effect | radiation intensity is greater on the cathode side |
| off focus radiation | photons that were not producted at the focal spot |
| heat units | kvp x mA x sec x c |
| causes of tube failure (4) | 1. overheating of anode 2. overheating of rotor assembly 3. overheating of filament 4. gassy tube |
| pitted anode | small pits on the surface of the focal track caused by too mnay exposures to the tube |
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