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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 |