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x-ray tubes
| Question | Answer |
|---|---|
| Thermionic Diode Tubes | 1. A hot metal filament that gives off electrons a. called thermionic emission b. heated by the filament current |
| Thermionic Diode Tubes | 2. If no kV is applied, the emitted electrons remain near the filament as an electron cloud, or space charge |
| Thermionic Diode Tubes | 3. When kV is applied, the space charge is driven to the anode at high speed |
| Thermionic Diode Tubes | 4. X-rays are produced from the kinetic energy of the electrons |
| Glass envelope | -Made from pyrex -contains a perfect vacuum (the tube is baked during manufacture to expel air and other gasses, called DEGASSING) -immerse in insulating oil |
| Cathode (negative terminal) | * filament *focusing cup |
| Filament | * measures about 2 mm in diameter and 10mm or less in length. * connected to two wires (high and low voltage) * usually need about 3-5amps * most x-ray tubes have 2 filaments |
| Focusing cup | molyboldenum collar that surrounds the filament wires |
| Anode | -stationary anode -rotating |
| Rotating anode | * came out in 1936 *was improved by adding molybdenum disc coated with a tungsten-rhenium alloy to serve as the focal track target * average speed is 3600rpm 10,000rpm high speed |
| Rotating anode | * Have various angles between 10-17 degrees *Usually have 2focal spots 0.6, 1mm * Tubes designed for magnification radiography with 0.3mm ( called fractional focus tubes) |
| Anode Heel Effect | The radiation intensity of the beam is greater on the cathode side |
| Line focus principle | The use of the angle on the target is used to increase the effectiveness of the focal spot. The effective focal spot is smaller than the actual focal spot |
| Extending tube life | filament life * tube rating ** anode should be warmed up ** bearing life ** Excessive oil life ** rapid sequence exposures **avoid overheating of the filament and anode |
Created by:
jhill106
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