X-Ray Units Flashcards
What is the purpose of the lead shield in X-ray units?
To prevent electrons from traveling outside of it
What is the purpose of the oil bath?
To absorb heat
What is the purpose of copper?
To absorb heat
What are the two components of the cathode?
filament
focusing cup
What are the two desired properties of the cathode?
electrical conductivity
high vapor pressure
How are electrons produced in the cathode?
By thermionic emission
The process by which the cathode filament is heated, the electrons are boiled off and the electrons are then accelerated toward a tungsten target is called ______.
thermionic emission
What is the sequence of thermionic emission and at what point are X-rays generated?
- Cathode
- Electrons
- Anode (X-rays generated here)
- X-rays
What are the three desired properties of the anode?
electrical conductivity
high melting point
high atomic number; i.e., Tungsten
To take advantage of a small focal spot while distributing the electrons over a larger area of the target, the target is placed at an angle to the electron beam. This is called ________.
line focus principle
True or False? The angle of the target to the central ray of the x-ray beam has a strong influence on the apparent size of the focal spot.
True
When are rotating anode tubes used?
When heavy use is demanded such as in hospitals
How are current and voltage related?
They are inversely related
The movement of electrons is known as _____.
electrical current
The rate of current is the number of electrons moving past a point in a second and is measured in ______.
amperes
The flow of electrons through the x-ray tube is referred to as _________.
tube current
Tube current is measured in _____.
milliamperes mA
The energy of the electrons is the _____.
voltage
Voltage is measured in ______ and in dental radiography in _______.
volts, kilovolts kV
______ translates to maximum energy of x-ray photons in a beam.
Peak kV or kVp
What is the potential difference between the anode and the cathode?
tube voltage
Tube voltage is measured in _____.
kVp or peak kilovoltage
What is the normal voltage for dental radiography?
60-70kV
What are the two primary functions of the power supply of an x-ray machine?
- provide a low voltage current to heat the x-ray tube filament by use of a step-down transformer
- generate a high potential difference between the anode and cathode by use of a high-voltage step up transformer
What reduces the voltage at the cathode from 110 to 10 volts which in turn requires an increase in the amperage of the filament circuit by a factor of ten from about 500mA to 5000 mA or 5 Amps?
step-down transformer
What transforms the 110 volts from the wall outlet to 65,000 to 70,000 volts which in turn requires a reduction in the amperage from 500mA to 5 to 7 Amps due to increased voltage?
Step-up transformer
What are the three purpose of recitification?
- increased efficiency
- shortened exposure time
- more reliable radiation output
What are the four purposes of X-ray generation?
- increased efficiency
- increased mean of energy of beam
- shortened exposure times
- more reliable radiation output
_____ relates to the frequency with which successive exposures can be made.
Duty cycle
What are the desired characteristics of x-ray tube housing?
- x-ray absorptive
- heat conductive
