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RAD 231 Unit 2
Question | Answer |
---|---|
What is space charge? | cloud of electrons that build up around filament; has a definite size for a given value of filament current in given tube |
What is the space charge effect? | electrons reach a point where the negative charges begin to oppose the emission of additional electrons |
What is the space charge compensator? | a device located in the filament circuit that automatically adjusts filament current to maintain constant mA over a wide range of kV; lowers filament current as kVp is raised to keep mA constant over the kV range; modern filament stabilizer |
*****What happens if no space charge compensator? | -Space-charge limited region - increasing kVp drives more electrons to anode (increase mA (tube current)); kVp cannot be independently changed from mA -Saturation current/temp limited region |
Name the two additional x-ray tube types | *Grid Controlled tube; *Fractional Focus x-ray tube |
Describe grid controlled tube. p170 Selman | generally found in portables on capacitor discharge unit; has a biased focusing cup (-2kV) acts as a switch to terminate flow of electrons at selected technique |
Describe fractional focus x-ray tube S p141; 226-227 |