XRT Flashcards
Area of anode struck by the electrons from the cathode
Target
An external casing containing the XRT
Protective Housing
Lead-lined aluminum alloy
Protective Housing
Protects against accidental electric shock and protects the tube from damage caused by rough handling
Protective Housing
Contains oil that serves as an insulator against electric shock and a thermal cushion to dissipate heat
Protective Housing
Some have a cooling fan to air cool the tube or the oil in which the XRT is immersed
Protective Housing
Vacuum-sealed enclosure surrounding the anode and cathode
Glass or metal enclosure/ envelope
30-50 cm long
Glass or metal enclosure/ envelope
20 cm in diameter
Glass or metal enclosure/ envelope
Maintains a vacuum inside the tube alloowing for a more efficient XR production and a longer tube life
Glass or metal enclosure/ envelope
5cm^2 thin
XR window/ port
area of the enclosure through which the useful beam is emitted
XR window/ port
thin pyrex glass or berrylium
XR window/ port
Allows maximum emission of x-rays with minimum absorption
XR window/ port
Thin coil of wire in which its diameter and length influence electron emission
Filament
2mm diameter
Filament
1 or 2 cm long
Filament
1-2% thorium
Filament
Thoriated tungsten
Filament
Negatively charged metal in which the depth of filament, shape, and charge are important determinants of its effectivity
Focusing cup
Nickel or copper
Focusing cup
Provides electrostatic repulsion
Focusing cup
Confines electron beam to a small area of the anode
Focusing cup
Has high voltage
Protective housing
100mR/ hr at 1m
Protective housing
Tube arcing
Glass enclosure/ envelope
XRT electrodes
Cathode and anode
Purpose of the 1-2% thorium in filament
Enhances thermionic emission efficiency and prolongs tube life
Acts as an exposure switch (in a grid-controlled XRT)
Focusing cup
Tungsten melting point
3410°C
0.1 to 1 mm
Small focal spots
0.3 to 2 mm
Large focal spots
10,000 rpm
High capacity target
3,400 rpm
Standard target
Filament receives (1); XRT receives (2)
- A
- mA
Serves as an electrical conductor
Anode
Rhenated tunsten
Target (Both rotating and stationary)
Abruptly degenerates and stops electrons in the tube current, allowing the production of x-rays
Target
May vaporize
Target
May have mollybdenum and graphite
Rotating target
7cm radius
Target
Atomic number, conductivity, and melting point are important characteristics
Target
Used in dental x-ray imaging systems, some portable imaging systems, and other special-purpose units in which high tube current and power are not required
Stationary anode x-ray tubes
General purpose XRTs
Rotating anode x-ray tube
Receives electrons emitted by the cathode and conducts them through the tube to the connecting cables and back to the high-voltage generator
Target
Most common anode materials
Copper, molybdenum, and graphite
Purpose of alloying targets with 10% rhenium
Withstands heat
1800mm^2
Rotating anode
Provides nearly 500 times more area to interact with the electron beam
Rotating anode
Higher tube currents and shorter exposure times
are possible with the —
rotating anode
Narrow so as to reduce its thermal conductivity
Anode stem
Poor heat conductor
Anode stem
Where the tungsten alloy target is embedded
Cu block
Allows heat conduction
Cu block
Mechanically supports the tungsten target and removes heat efficiently from the target
Cu block
Used to turn the anode
Elevtromagnetic induction
Shaft inside the enclosure rigidly connected tot he target through the anode stem
Rotor
Bars of cu and soft iron
Rotor
Causes the target to rapidly rotate during XR productino
Rotor
High strength ball bearings allow it to smoothly rotate at high speeds
Rotor
Stationary coil windings
Stator
Series of electromagnets
Stator
An electric motor that induces the rotor to spin at a very high speed
Stator
Conductino as heat dissipation technique
Stationary anode
Induction (Radiation) as heat dissipating technique
Rotating anode
Produces space charge
Filament
Provides smooth flow of electrons in tube
Focusing cup
Provides both xrs and heat
Target
Responsible in sustaining heat in target
Anode stem
