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RADT 334
Radiation Physics- Chapter 6
| Question | Answer |
|---|---|
| Defend the choice of material used most frequently in the filament. | Thoriated tungsten, provides for higher thermionic emission than other metals, melting point 3410C |
| List three causes of tube failure and how to prevent them. | Excessive heat results in reduced x-ray tube life, maximum radiographic techniques should never be applied to a cold anode, and most frequent is electron arcing from the filament to the enclosure because of vaporized tungsten |
| External components of the x-ray tube | Quite heavy so there has to be kind of support system, there is also a protective housing, and a glass or metal enclosure |
| Three kinds of support systems | Floor-to-ceiling, ceiling, and c-arm |
| Internal components of the x-ray tube | Anode and cathode |
| Anode | Positive side of the x-ray tube and it conducts electricity and radiates heat and contains the target |
| Cathode | Negative side of the x-ray tube |
| Two parts of the cathode | Filament and focusing cup |
| Filament | Coil of wire, 2mm in diameter and 1-2 cm long, electric current is conducted through the coil causing it to glow and emit a large quantity of heat |
| Focusing cup | The filament is embedded in a metal shroud, effectiveness is determined by its size, shape, and the position of the filament |
| Protective housing | Controls leakage and scatter radiation, isolates the high voltage, and provides a means to cool the tube |
| Glass or metal enclosure | X-ray tube is a vacuum containing two electrodes (anode and cathode) |
| Improved metal enclosures | Maintain a constant electric potential between electrons of the tube current and the enclosure |
| Electron cloud | Space charge (when the electrons are in vicinity of the filament before acceleration to anode) |
| Space charge effect | The cloud of electrons makes it hard for subsequent electrons to be emitted because of electrostatic repulsion |
| Saturation current | Tube current rises with increasing voltage to a maximum value |
| Ceiling support system | Most used, two perpendicular sets of ceiling-mounted rails, preferred in detent |
| Floor-to-ceiling support system | Single column with rollers on each end, one attached to a ceiling-mounted rail and the other attached to a floor-mounted rail |
| C-arm support system | Ceiling mounted and provide very flexible x-ray tube positioning |
| Small focal spot | Used when better spatial resolution is required (bone work) |
| Large focal spot | When large body parts are imaged and when higher techniques are used that will generate high heat |
| Three functions of an anode | Electrical conductor, mechanical support for the target, and thermal dissipater |
| Whats is the anode made up of? | Tungsten (high atomic number, high melting point), molybdenum, and graphite (lower mass density, high melting point) |
| Stationary anode | 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 |
| Rotating anode | Capable of producing high-intensity x-ray beams in a short time, |
| Line focus principle | The focal spot is the area of the target from which x-rays are emitted; requires smaller focal spot to get better spatial resolution |
| Anode heel-effect | Weaker intensity of x-ray beam on anode side, the smaller the anode angle, the larger the effect, used on feet, chest, and abdomen |
| X-ray tube rating | Charts that guide the technologist in the use of x-ray tubes |
| Cooling chart | Thermal capacity of an anode, and its heat dissipation characteristics are contained in a rating chart |
| Create a list of properties to support the choice of material mostly used for the anode target in general radiography | Tungsten is the material used in the general radiography, used for 3 reasons: high atomic number, thermal conductivity, and high melting point |
Created by:
meechthebeech91
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