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RADT 334
Radiation physics- unit 3
| Question | Answer |
|---|---|
| A material that can conduct an electric current or not, depending on the voltage applied across that material | semi conductor |
| An electronic device designed to terminate x-ray exposure after properly exposing an image receptor | AEC |
| A method of adjusting the voltage to the x-ray imaging system to a constant value, in response to changes in voltage supplied by the power company | line compensator |
| An electrical circuit device that stores electric charge | capacitor |
| Placed in the tube circuit, connected at the center of the secondary winding of the high-voltage step-up transformer in series with the x-ray tube. This reduces the possibility of shock. | mA meter location |
| An electrical device that contains two electrodes | diode |
| The fluctuation in the voltage applied to the x-ray tube expressed as a percentage of peak kilovoltage | voltage ripple |
| The process of changing alternating current and voltage into direct current and voltage | rectification |
| A type of transformer having a single winding | autotransformer |
| The product of voltage and current. Watt. | power |
| 220 V is supplied across 1200 windings of the primary coil of the autotransformer. If 1650 windings are tapped, what voltage will be supplied to the primary coil of the high-voltage transformer? | 302.5 V |
| A kVp meter reads 86 kVp and the turns ratio of the high-voltage step-up transformer is 1200. What is the true voltage across the meter? | 71.7 volt peak |
| The supply voltage from the autotransformer to the filament transformer is 60 V. If the turns ratio of the filament transformer is 1/12, what is the filament voltage? | 5 V |
| If the current in the primary of the filament transformer was 0.5 A with a turns ratio of 1/12, what would be the filament current? | 6 amps |
| Allows relatively undiminished intensity of x-rays through the tabletop | radiolucent |
| Allow relatively undiminished intensity of x-rays through the tabletop | 90/20 table |
| List the five major controls on the operator's console. | On/off control, kVp selection, mA selection, time (mAs) selection, and automatic-exposure controls |
| purpose of the autotransformer | To vary and control the amplitude of the voltage supplied to the high-voltage step-up transformer and the filament transformer |
| Primary voltage and secondary voltage are in direct relation to the number of turns of the transformer | primary/secondary voltage relationship in autotransformer |
| What the prereading kVp meter allows | The precise adjustment of the supply voltage and monitoring the kVp before the x-ray exposure |
| 200 mA, 1/60s= what mAs? | 3.3 |
| 600 mA, 30 ms = what mAs? | 18 |
| Difference between high voltage transformer and high voltage generator | The high-voltage transformer is just one component of a high-voltage generator. |
| In order that a reverse voltage is not applied across the x-ray tube and that the tube operates most efficiently, x-ray tubes use ___ current. | direct |
| Direct current is achieved in the x-ray circuit through ______. | rectification |
| Voltage ripple of single-phase generator | 100% |
| Voltage ripple of three-phase, six-pulse generator | 14% |
| Voltage ripple of three-phase, twelve-pulse generator | 4% |
| Voltage ripple of high-frequency generator | 1% |
| 0.7 (mA)(kVp)/1000 is the equation for computing ______ power rating | single-phase |
| (mA)(kVp) / 1000 is the equation for computing ______ or _______ power ratings. | three-phase, high-frequency |
| housing cooling chart | Graph showing the cooling rate of an x-ray tube housing |
| leakage radiation | Radiation emitted through the x-ray tube housing (other than the primary beam) |
| Measure of heat capacity (1HU = 1AVs = 1Ws =1J) | heat unit |
| Shroud inside the x-ray tube surrounding the cathode to concentrate electrons on the focal spot | focusing cup |
| anode rotation speed | 3400 rpm or 10,000 rpm |
| thoriated tungsten | Tungsten alloyed with thorium |
| x-ray tube current | Cathode to anode electron flow |
| X-ray tube capable of high speed switching. Voltage applied to the focusing cup is the switch. | grid-controlled x-ray tube |
| Method of heat transfer by a moving fluid medium (liquid or gas) | convection |
| Electron cloud in the vicinity of the filament | space charge |
| Three methods used to support the x-ray tube | floor, wall, or ceiling mounted |
| Where thoriated tungsten would be used in a x-ray imaging system | cathode and anode |
| When all available electrons are projected from the cathode to the anode | saturation current |
| Why are arcing and tube failure no longer a problem in modern x-ray tube design? | heavy filaments and high capacity anodes |
| Pass an electric current to heat a conductor and cause outer-shell electrons to be released from the conductor | thermionic emission |
| Principal cause of tube failure | tube arching |
| What addition to the filament material prolongs tube life? | thorium |
| Why is the filament embedded in the focusing cup? | to electrostatically shape beam |
| Why would an x-ray tube need a small focal spot? | better spatial resolution |
| Why would an x-ray tube need a large focal spot? | high intensity radiation |
| Negative side of the x-ray tube | cathode |
| positive side of the x-ray tube | anode |
| Name two type of anodes | fixed and rotating |
| three functions of anode | 1)x-ray tube target 2)electrical and thermal conductor 3)mechanical support |
| How does atomic number affect the selection of anode target material? | high atomic number = efficient x-ray production |
| How does thermal conductivity affect the selection of anode target material? | thermal conductivity = heat dissipation |
| How does melting point affect the selection of anode target material? | melting point = heat capacity |
| How does the anode rotate inside a glass enclosure with no mechanical connection to the outside? | induction motor |
| Higher x-ray intensity on cathode side | anode heel effect |
| How can anode heel effect be used advantageously? | positioning thicker anatomy on cathode side |
| Name three causes of tube failure | cracked or pitted anode, induction motor failure, and open filament |
| How can a space charge be removed? | increase kV |
| X-ray tube locking-in at center and at a given SID | detent position |
| part of the x-ray circuit that contains the kvp selector, kvp meter, exposure timer and exposure switch | primary side/circuit |
| part of the x-ray circut that contains the mA selector, focal spot selector and step-down transformer | filament circuit |
| part of the x-ray circuit that contains the mA meter and rectifiers | secondary side/circuit |
| adjusts autotransformer to deliver precisely 220 volts | line voltage compensator |
| supplies a precise voltage to the high voltage circuit | autotransformer |
| reads the voltage that will be applied to the secondary side of the step up transformer | kVp meter |
| filament uses this current | 3 to 6 A |
| this is what happens to current when voltage is increased | decreased |
| this is what happens to voltage when current is increased | decreased |
| type of timer that has a minimum exposure time of 1/60 s and has to be reset each time exposure is made | synchronous |
| type of timer that is the most accurate but also most sophisticated and complicated | electronic |
| type of timer that monitors the product of mA and exposure time and terminates the exposure when desired mAs value is attained; used on falling load imaging systems | mAs |
| type of timer that measures the quantity of radiation reaching the image receptor and terminates the exposure when the image receptor has received enough radiation to provide the required optical density | AEC |
| most commonly used AEC | ionization chamber |
| type of rectifiers used in x-ray imaging systems today | solid-state |
| if positive charge is applied to the n side of the solid state rectifier then electrons____ flow | will not |
| if negative charge is applied to the n side of the solid state rectifier then electrons _____ flow | will |
| number of rectifiers used in half-wave rectification | two |
| number of rectifiers used in full-wave rectification | four |
| number of pulses per second with half wave rectification | 60 |
| number of pulses per second with full wave rectification | 120 |
| number of pulses per second with three phase power (non rectified/6 pulse) | 360 |
| number of pulses per second with three phase power (rectified/12 pulse) | 720 |
| type of generator that generates high voltage, full-wave rectified power to a higher frequency (usually 500-25,000 Hz) | high-frequency |
| type of generator used in portable machines | high-frequency |
| type of generator that builds up a charge then releases it with completion of the circuit | capacitor-discharge |
| type of generator that is used to provide the highest mA setting at the shortest possible times where the computer will automatically calibrate the time of the exposure allowing consistently shorter exposures | falling-load generator |
| voltage ripple percent for single phase half wave rectified units | 100 |
| voltage ripple percent for single phase full wave rectified units | 100 |
| voltage ripple percent for three phase, six pulse units | 13 |
| voltage ripple percent for three phase, twelve pulse units | 4 |
| voltage ripple percent for three phase, high frequency units | less than 1 |
| X-ray production efficiency ______ with an increase in voltage ripple | decreases |
| High frequency generators cost _____ than single phase generators | more |
| multiplying mA and kVp then dividing by 1000 is the equation for power rating for _______. | three phase and high frequency |
| multiplying 0.7, mA, and kVp then dividing by 1000 is the equation for power rating for _____. | single phase units |
Created by:
meechthebeech91
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