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RADT 334 X-ray tube
radiographic physics review covering x-ray tube
| Question | Answer |
|---|---|
| What are the 5 main components of the X-ray tube? | Support system, protective housing, enclosure, cathode, anode |
| What are the external parts of the X-ray tube? | Support system, protective housing, enclosure |
| What are the internal parts of the X-ray tube? | Cathode and Anode |
| What guards against excessive radiation exposure and electric shock and controls leakage and scatter radiation, isolates the high voltages and provides a means to cool the tube? | protective housing |
| What is the x-ray tube components contained within? | glass or metal enclosure |
| This maintains a constant electric potential between the electrons of the tube current and the enclosure | metal enclosure tubes |
| What is a vacuum containing two electrodes? | x-ray tube |
| What are the two electrodes of the x-ray tube? | anode and cathode |
| What is the glass or metal enclosure usually made of? | Pyrex |
| What is the negative side of the x-ray tube? | cathode |
| What are the two primary parts of the cathode? | filament and focusing cup |
| coil of wire that emits electrons when heated | filament |
| where the filament is embedded negatively charged to keep electron beam to a small area of the anode | focusing cup |
| when the cloud of electrons make it hard for subsequent electrons to be emitted because of electrostatic repulsion | space charge effect |
| what is the phenomenon called when the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are "boiled-off" and ejected from the filament | thermionic emission |
| what are filaments usually made of | thoriated tungsten |
| what is the most common cause of tube failure | tungsten vaporization with deposition in the inside of the glass enclosure |
| why are filaments usually made out of tungsten? | because tungsten provides for higher thermionic emission than other metals; also does not vaporize easily |
| how is the x-ray tube current adjusted? | by controlling the filament circuit |
| which focal spot is used when better spatial resolution is required (bone work) | small focal spot |
| which focal spot is used when large body parts are imaged and when higher techniques are used to generate high heat | large focal spot |
| what is the positive side of the x-ray tube that conducts electricity and radiates heat and contains the target | anode |
| what are the two types of anodes? | rotating and stationary |
| what are the three functions of the anode | electrical conductor, mechanical support for the target, and thermal dissipater |
| what is the area of the anode struck by the electrons from the cathode | target |
| why is tungsten the material of choice for the target | high atomic number, thermal conductivity, and high melting point |
| why is molybdenum and graphite used for the anode? | lower mass density (lighter) and high melting point |
| what is possible with the rotating anode? | higher tube currents and shorter exposure times |
| what is the rotating anode powered by? | an electromagnetic induction motor |
| what is the actual x-ray source (where x-rays are emitted) | the focal spot |
| the area projected onto the patient and image receptor | effective focal spot |
| where electron interacts with target | actual focal spot |
| what does the the line-focus principle result in? | an effective focal spot size much less than the actual focal spot size |
| the smaller the anode angle, the ____ the heel effect | larger |
| what does the heel effect result in? | smaller effective focal spot and less radiation intensity on the anode side of the x-ray beam |
| What are some examples where the anode heel effect would be used to an advantage? | foot, chest, abdomen |
| what does excessive heat result in? | reduced x-ray tube life |
| what is the most frequent cause of abrupt failure | electron arcing |
| three important types of x-ray tube rating charts | radiographic rating chart, anode cooling chart, and housing cooling chart |
| which is the most important x-ray tube rating chart because it conveys which radiographic techniques are safe and unsafe for tube operation | radiographic rating chart |
| why would a rotating anode be used. | to produce high-intensity x-ray beams in a short time |
| when would a stationary anode be ideal? | when high tube current and power are not required; examples, dental imaging systems and portable imaging systems |
| the thermal capacity of an anode and its heat dissipation characteristics are contained in this rating chart | anode cooling chart |
| most frequent cause of abrupt tube failure | electron arcing from the filament to the enclosure because of vaporized tungsten |
| two ways tube failure can occur | from maintaining the anode at elevated temperatures for prolonged periods and from increasing the temperature of the anode too rapidly causing the anode to crack |
Created by:
haleygesselman
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