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RADT 334: X-ray Tube

Radiographic Physics Review Covering X-Ray Tube

QuestionAnswer
What is the purpose of the protective housing? To guard against excessive radiation exposure and electric shock
Which side of the x-ray tube is the negative side? Cathode
Which side of the x-ray tube is the positive side? Anode
How are x-rays emitted? Isotropically
The x-rays emitted through the window are called? The useful beam
X-rays that escape through the protective housing are called? Leakage radiation
When operated at maximum conditions, the properly designed protective housing reduces the level of leakage radiation to what? Less than 1 mGya/hr at 1 m
An x-ray tube is an electronic vacuum tube with components contained within what type of enclosure? Glass or metal
What is the glass enclosure made of? Pyrex glass
What enclosure maintains a constant electric potential between the electrons of the tube current and the enclosure? Metal enclosure tubes
Where is the useful beam of x-rays emitted from? The window
Which side of the x-ray tube contains the filament and focusing cup? Cathode
Which side of the x-ray tube conducts electricity, radiates heat, and contains the target? Anode
What does the filament do? Emit electrons when it is heated
What is the process called of the outer electrons are "boiled off" and ejected from the filament? Thermionic emission
What is the filament usually made of? Thoriated tungsten
Why is tungsten used? Provides for higher thermionic emission than other metals with a melting point of 3410 degrees Celsius and does not vaporize easily
What is the purpose of the focusing cup? Confines the electron beam to a small area of the anode
What is space charge? When emitted from the filament, electrons are in the vicinity of the filament before they are accelerated to the anode. Because of the negative charge, they repel one another to form a cloud.
What are the two types of anodes? Stationary and rotating
Why are rotating anodes used in general-purpose x-ray tubes? Because they must be capable of producing high-intensity x-ray beams in a short time
What is the target? The area of the anode struck by the electrons from the cathode
What is possible with a rotating anode? Higher tube currents and shorter exposure times
What is used to turn the anode? An electromagnetic induction motor
What is the actual x-ray source? The focal spot
The line-focus principle results in what? An effective focal spot size much less than the actual focal spot size
What does the heel effect result in? Reduced x-ray intensity on the anode side of the useful beam caused by absorption in the "heel" of the target
What is a second result of the heel effect? Results in smaller effective focal spot and less radiation intensity on the anode side of the x-ray beam
What can reduce x-ray tube life? Excessive heat
What are the three ways heat can be dissipated? Radiation, Conduction, and Convection
Most of the heat is dissipated by which type? Radiation
What is the most frequent cause of abrupt tube failure? Electrons arcing from the filament to the enclosure because of vaporized tungsten
What is the second type of x-ray tube failure? Results from maintaining the anode at elevated temperatures for prolonged periods
What is an anode cooling chart? The thermal capacity of an anode, and its heat dissipation characteristics are contained in a rating chart
What are the external components of the x-ray tube? Ceiling Support System, Floor-to-Ceiling Support System, C-Arm Support System, Protective Housing, Glass or Metal Enclosure
What are the internal components of the x-ray tube? Cathode, Anode
Created by: krsteffen