Chapter 3 Flashcards
Increasing which of the following would best increase the number of electrons flowing through the dental x-ray electrical circuit?
C) Milliamperage
An increase in amperage results in an increase in the number of electrons that is available to travel from the cathode to anode when the tube is activated. This results in the production of more x-rays.
Which of the following removes the soft x-rays for the x-ray beam as it exits the port?
C) Filter
To remove the soft x-rays, a thin sheet of aluminum called a ‘filter’ is placed in the path of the x-ray beam.
How does the radiographer know when the x-ray exposure cycle is complete?
B) When the audible beep stops
When the exposure button is activated, the operator will hear an audible beep (required by law) that indicates x-rays are being generated. When the audible beep stops, the x-ray exposure cycle is complete.
Electricity is defined as electrons in motion.
TRUE
An electric current is the movement of electrons through a conducting medium (e.g., a copper wire).
The metal housing of the tube head increases the safety of the x-ray machine.
TRUE
The metal housing of the tube head increases the safety of the x-ray machine by grounding the high-voltage components (the x-ray tube and transformers) to prevent electric shock.
Direct current flows in pulses and changes direction.
FALSE
Direct current is unidirectional and flows continuously, while alternating current flows in pulses and changes direction.
Voltage is the measurement of the number of electrons moving through a wire conductor.
FALSE
Voltage is the measurement of electrical force that causes electrons to flow through a conductor. Amperage is the measurement of the number of electrons moving through a wire conductor.
If the tube head is properly sealed, the port is the only place through which x-rays can escape.
TRUE
X-rays produced within the tube are emitted in all directions within the tube housing. A thin window is located in the glass envelope at a point where emission of x-rays is most intense.
The x-ray beam formed at the focal spot is monochromatic.
FALSE
The x-ray beam formed at the focal spot is polychromatic because it consists of x-rays of various wavelengths.
The intensity of the beam refers to the quantity and quality of the x-rays.
TRUE
Quantity refers to the number of x-rays in the beam. Quality is a measure of the energy or penetrating ability of the beam.
The filament is on the negative side of the vacuum tube in the dental x-ray machine.
TRUE
A thin, spiral filament of tungsten wire, recessed into a molybdenum focusing cup, forms the cathode, which is negatively charged during the production of electrons.
Dental x-ray machines may have controls for manual adjustment of kVp and mA, or these controls may be preset by the manufacturer.
TRUE
Some machines have variable controls allowing the radiographer to adjust the kVp and mA of incoming electricity.
In the on position, the line switch on the control panel energizes the low- and high-voltage circuits.
FALSE
In the on position, the line switch energizes the circuits in the control panel but not the low- or high-voltage circuits.
Increasing the amperage will result in a production of more x-rays.
TRUE
An increase in amperage results in an increase in the number of electrons that is available to travel from the cathode to anode when the tube is activated.
That part of the cathode designed to direct the free electrons toward the tungsten target of the anode is called the ‘focal spot.’
FALSE
That part of the cathode designed to direct the free electrons toward the tungsten target of the anode is called the focusing cup.
The tungsten anode is embedded in a core of copper to conduct heat away to a radiator.
TRUE
Copper has a high thermal conductivity and carries the heat produced at the target off to the radiator.
A small area on the tungsten target of the anode toward which the electron beam is directed is called the ‘focal spot.’
TRUE
The focal spot is a small rectangular area on the target of the anode to which the focusing cup directs the electron beam.
The step-down transformer corrects fluctuations in the current flowing through the x-ray machine.
FALSE
The autotransformer corrects fluctuations in the current flowing through the x-ray machine.
The anode is the negative electrode (terminal) in the x-ray tube.
FALSE
The cathode is the negative electrode (terminal) in the x-ray tube.
The collimator is a lead diaphragm that restricts the dimensions of the useful beam.
TRUE
The lead collimator further restricts the x-ray beam to the desired size.
Thermionic emission refers to the release of electrons from the target material during the process of incandescence.
FALSE
Heating the filament of tungsten wire to incandescence produces the electrons.
Primary beam refers to a high-energy, short wavelength x-ray beam.
FALSE
Radiation that emanates at the focal spot of the x-ray tube and emerges through the aperture of the tube head is called the ‘primary beam.’
An x-ray beam composed of many different wavelengths is called ‘polychromatic.’
TRUE
A polychromatic beam is produced when the voltage varies during an exposure.
What does adjusting the kilovolt peak (kV) do?
Adjusting the kV changes the penetrating ability of the x-rays.
The kV selected determines the speed of electrons traveling from the cathode to the anode.
What is the name of the device that allows the amount of current passing through the wires of the circuit to be changed?
The milliamperage (mA) selector determines the available number of free electrons at the cathode filament.
Why are the extension arm and yoke of the x-ray machine insulated?
All sections of the extension arm and yoke are heavily insulated to protect the patient and operator from electrical shock.
What is the term for the measurement of the number of electrons moving through a wire conductor?
Amperage measures the number of electrons that move through a conductor.
Inside the dental x-ray machine, what does the speed of the electrons determine?
The speed of the electrons determines the energy (penetrating power) of the x-rays produced.
Who is responsible for the radiation dose incurred by the patient during x-ray exposure?
Although a dentist prescribes the radiographs, the dentist, dental assistant, or dental hygienist may expose the image.
What does kV measure?
kV measures the speed of the electrons, and therefore the penetrating ability of the x-ray beam.
What is the purpose of a ‘dead-man’ exposure switch?
Required by law, the purpose of the dead-man switch is safety. X-rays cannot be generated unless the radiographer’s finger is actively depressing the button.
What is the term for the process by which electrons are created at the filament wire of the cathode?
Thermionic emission occurs when a wire is heated to incandescence.
In the cathode, the wire filament is recessed into what?
The wire filament is embedded in a focusing cup made of molybdenum.
