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RADT 334

x ray tube

QuestionAnswer
What are the internal components of the x-ray tube and which side is positive and negative? The cathode is negative and the anode is positive.
What is the function of the cathode and what are its primary parts? The cathode has a filament and a focusing cup and its purpose is to provide a focal spot
What is the function of the anode? The anode contains the target for the cathode, conducts electricity, and radiates heat.
As a glass enclosure ages, what does this do to the longevity of the x ray tube? The vaporization of tungsten coats the inside of the glass and this causes straying of tube current resulting in tube failure.
Why is a metal enclosure better than a glass enclosure? Metal housings have a constant electric potential between the electrons and the enclosure resulting in a longer tube life.
Why is thoriated tungsten the material used mostly to make the filaments in the cathode? Tungsten has a higher thermionic emission, its melting point is 3410 degrees Celsius, and it does not vaporize easily.
Why does the cathode have two focal spots? The small focal spot associates with the small filament and the large focal spot associates with the large filament
When would a small focal spot be desired? When better spatial resolution is wanted
When would a large focal spot be desired? When a large body part is being imaged and when high heat is required
What is space-charge effect? When the space charge makes it difficult for enough electrons to be emitted by the filament due to electrostatic repulsion
What are the two different kinds of anodes? Stationary and rotating
Why would a stationary anode be used? When high tube current and power are not required, such as in dental imaging
Why would a rotating anode be used? When the production of high-intensity x-ray beams are required in a short time
What are the three most common anode materials? Copper, molybdenum, and graphite
Why is molybdenum and graphite used for the anode? Both have a lower density than tungsten, which makes the anode lighter and allows easier rotation
Describe the line-focus principle A design in x-ray tube targets allowing a large area for heating while using a small focal spot
Does the line-focus principle improve spatial resolution and heat capacity? Yes
Describe the anode heel-effect Where x-rays are absorbed into the heel of the target, which results in reduced x-ray intensity to the anode side
What are three causes of tube failure? Tungsten vaporization, the temperature of the anode increasing too rapidly causing the anode to crack, and excessive heating of the filament for prolonged periods causing open filament
What does an anode cooling chart demonstrate? The thermal capacity and heat dissipation characteristics of an anode
Created by: cfdishon