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Champa Ch 6

X-Ray Tube

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