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X-Ray Tube RAD 147
Part 3
| Question | Answer |
|---|---|
| Source of Electrons- | Cathode/Filament |
| Method to accelerate the electrons- | Voltage/Potential Difference |
| Method to quickly stop the electrons | Anode/Target (Causing energy transformation) |
| _______ Protects tube from damage and Minimizes leakage radiation | Protective Housing |
| _______ Guards against electric shock | Specialized Cables |
| _______ Cools tube and dissipates heat | Oil Bath & Fans |
| _______ Allows emission of the primary beam | Housing Window/Aperture |
| ______ Is Where the magic happens | X-Ray Tube |
| _______ leads to “gassy tube”, arcing, and reduced efficiency | Loss of Vacuum |
| First tubes with gas | Crookes Tubes |
| Vacuum Sealed, Model for today’s tube | Coolidge Tubes |
| Negative side of the x-ray tube | Cathode |
| Cathode Functions | Thermionic emission Focus electrons toward the anode |
| Filament is composed of | Thoriated Tungsten |
| ______ Enhances thermionic emission efficiency | Thorium (1-2%) |
| Thermionic Emission Step 1 | Filament gets hot |
| Thermionic Emission Step 2 | Electron Cloud (No large positive charge on the anode yet) |
| Thermionic Emission Step 3 | Space Charge Effect (Electron cloud is negative, repels new electrons back toward the filament) |
| Electron cloud is ________, repels new electrons back toward the filament | Negative |
| General purpose x-ray tubes will not exceed | 1000 mA |
| An unintended electrical discharge inside the x-ray tube – Electrons jump to another nearby metal surface instead of anode | Arcing |
| Possible causes of Arcing- | – Tungsten vapor deposits inside glass envelope – Extremely high voltages that exceed the tube's insulating ability |
| Possible consequences of Arcing- | – Damage the anode, cathode or tube – Produce poor or failed x-ray exposures |
| The Focusing Cup is made of _____ | Nickel |
| Focusing Cup Functions | Narrow thermionic cloud & direct electrons toward the anode |
| Without the Focusing Cup- | Electrons disperse too widely |
| With the Focusing Cup- | Narrow stream of electrons toward focal spot |
| The Focusing Cup has a _________ focusing the electrons | Negative charge from the secondary circuit |
| The Space Charge Effect- | Limits the number of electrons emitted |
| Electron Cloud- | Electrons “hover” around the filament |
| Higher mA = more heat = | More Electrons Boiling Off |
| The limiting action of the electron cloud which prevents more electrons from escaping the filament regardless of how much hotter the filament gets | Space Charge Effect |
| Metal cover with filaments embedded in shallow depression- | Focusing Cup |
| Exceeding the filaments heat limit increases | Filament evaporation/Filament breakage Metal deposited inside glass envelope Arcing and Tube wear (shorter tube life) |
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