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Champa Ch 6
X-Ray Tube
| Question | Answer |
|---|---|
| Isotropic Emission | Spherical pattern, x-rays fly off in all directions |
| Cathode Assembly | Filament, Focusing Cup, Wiring |
| Filament | Coiled Tungsten Wire |
| Focusing Cup | Direct and Concentrate Beam |
| Thermionic Emission | The boiling off of electrons due to heat from current running through filament |
| Space Charge | Where boiled off electrons hang out |
| Why Tungsten Filament | Low Vaporization, High Melting Point |
| Focusing Cup | Made of Nickel and surrounds the filament |
| Focusing Cup | Negatively Charged |
| Dual Focus | Two Filaments, one large and one small |
| Vaporization | Reduces vacuum, causes high voltage arching, increases filtration of primary beam |
| Average Tube Life | 6 -9 hrs., 10,000 - 20,000 exposures |
| Causes of Tube Failure | Arching, Filament Breakage |
| Anode | Target for Electrons |
| Rotating Anode | 3300 - 3600 RPM |
| Rotor | Made of copper to draw away excessive heat |
| Wheel | Molybdenum |
| Focal Spot | Where Electrons Hit Anode |
| Focal Track | Made of Tungsten-Rhenium Alloy |
| Tungsten-Rhenium Alloy | High Melting Point, High Atomic Number, Good Heat Conductor |
| Pitting | Caused from Heat and Failure of Rotor |
| Anode Functions | Target Surface, Conducts High Voltage Back Into X-Ray Generator, Primary Heat Conductor |
| Grid Bias Tube | Used When Exposure Needs To Be Turned Off Quickly |
| Positively Charged Focusing Cup | Grid Bias Tube |
| 3rd Wire In Grid Bias Tube | Focusing Cup |
| Actual Focal Spot | Cathode to Anode |
| Effective Focal Spot | Anode to Film |
| Small Angle | Small Focal Spot |
| Smaller Beam | More Detail |
| Most common Anode Angle | 12 Degrees |
| Size of effective focal spot is controlled by | Size of filament, Angle of Anode |
| Magnification Radiography | Fractional Focal Spots- (Under 1mm) |
| Anode Heel Effect | Cathode side of tube produces more x-ray because anode absorbs rays that are deflected towards it |
| Stator | Located outside of glass envelope, makes rotor turn |
| Ball Bearings | Ensure no wobble when rotor turns |
| Silver coated ball bearings | High heat and no lubrication |
| Glass Envelope | Pyrex |
| Degassing | Creates vacuum inside glass envelope and prevents blocking of electrons and x-ray photons |
| Window | Area where beam comes out of tube |
| Thin window | Won't absorb (filter out) x-rays |
| Protective Housing | Blocks stray radiation, Helps get rid of heat |
| Dielectric oil | Insulator and heat absorber |
| Oil between window and housing | Dielectric |
| Functions of the Tube Housing | Absorbs scatter and leakage radiation, Insulates and Absorbs Heat, Protects the tube from breakage |
| Leakage radiation | Must be < 100 mR/hr at 1 meter |
| Off focus radiation | Not produced at Focal spot |
| Follows anatomy and reveals soft tissue | Leakage or off focus radiation |
| Scatter Radiation | Covers entire film and creates fog |
| Electro magnet | Stator |
| Manual warm up | Low energy and long exposure time |
Created by:
Ranapipins
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