RADT 334 - Unit 3

semiconductor

A material that can conduct an electric current or not, depending on the voltage applied across that material

AEC

An electronic device designed to terminate x-ray exposure after properly exposing an image receptor

line compensation

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

capacitor

An electrical circuit device that stores electric charge

mA meter location

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.

diode

An electrical device that contains two electrodes

voltage ripple

The fluctuation in the voltage applied to the x-ray tube expressed as a percentage of peak kilovoltage

rectification

The process of changing alternating current and voltage into direct current and voltage

autotransformer

A type of transformer having a single winding

power

The product of voltage and current. Watt.

302.5 V

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?

71.7 volt peak

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?

5 V

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?

6 amps

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?

104.5 kV

The suply to a high-voltage step-up transformer with a turns ratio of 550 is 190 V. What is the voltage across the x-ray tube?

radiolucent

Allows relatively undiminished intensity of x-rays through the tabletop

90/20 table

Allow relatively undiminished intensity of x-rays through the tabletop

10. On/off control, kVp selection, mA selection, time (mAs) selection, and automatic-exposure controls

List the five major controls on the operator's console.

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/secondary voltage relationship in autotransformer

Primary voltage and secondary voltage are in direct relation to the number of turns of the transformer

What the prereading kVp meter allows

The precise adjustment of the supply voltage and monitoring the kVp before the x-ray exposure

3.3

200 mA, 1/60s= what mAs?

18

600 mA, 30 ms = what mAs?

Difference between high voltage transformer and high voltage generator

The high-voltage transformer is just one component of a high-voltage generator.

direct

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.

rectification

Direct current is achieved in the x-ray circuit through ______.

100%

Voltage ripple of single-phase generator

14%

Voltage ripple of three-phase, six-pulse generator

4%

Voltage ripple of three-phase, twelve-pulse generator

1%

Voltage ripple of high-frequency generator

single-phase

0.7 (mA)(kVp)/1000 is the equation for computing ______ power rating

three-phase, high-frequency

(mA)(kVp) / 1000 is the equation for computing ______ or _______ power ratings.

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)

heat unit

Measure of heat capacity (1HU = 1AVs = 1Ws =1J)

focusing cup

Shroud inside the x-ray tube surrounding the cathode to concentrate electrons on the focal spot

anode rotation speed

3400 rpm or 10,000 rpm

thoriated tungsten

Tungsten alloyed with thorium

x-ray tube current

Cathode to anode electron flow

grid-controlled x-ray tube

X-ray tube capable of high speed switching. Voltage applied to the focusing cup is the switch.

convection

Method of heat transfer by a moving fluid medium (liquid or gas)

space charge

Electron cloud in the vicinity of the filament

floor, wall, or ceiling mounted

Three methods used to support the x-ray tube

cathode and anode

Where thoriated tungsten would be used in a x-ray imaging system

saturation current

When all available electrons are projected from the cathode to the anode

heavy filaments and high capacity anodes

why are arcing and tube failure no longer a problem in modern x-ray tube design?

thermionic emission

Pass an electric current to heat a conductor and cause outer-shell electrons to be released from the conductor

tube arcing

Principal cause of tube failure

thorium

What addition to the filament material prolongs tube life?

to electrostatically shape beam

Why is the filament embedded in the focusing cup?

better spatial resolution

Why would an x-ray tube need a small focal spot?

high intensity radiation

Why would an x-ray tube need a large focal spot?

cathode

Negative side of the x-ray tube

anode

positive side of the x-ray tube

fixed and rotating

Name two type of anodes

three functions of anode

1)x-ray tube target

2)electrical and thermal conductor

3)mechanical support

high atomic number = efficient x-ray production

How does atomic number affect the selection of anode target material?

thermal conductivity = heat dissipation

How does thermal conductivity affect the selection of anode target material?

melting point = heat capacity

How does melting point affect the selection of anode target material?

induction motor

How does the anode rotate inside a glass enclosure with no mechanical connection to the outside?

anode heel effect

Higher x-ray intensity on cathode side

positioning thicker anatomy on cathode side

How can anode heel effect be used advantageously?

cracked or pitted anode, induction motor failure, and open filament

Name three causes of tube failure

increase kV

How can a space charge be removed?

detent position

X-ray tube locking-in at center and at a given SID