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RADT 334
x ray tube
Question | Answer |
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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 |