oral rad unit 4 (study guide)

what is wavelength?

the distance form the crest of one wave to the crest of the next

what is frequency?

the number of wavelengths passing a point in a specific length of time

what is velocity?

the speed of the wave

what is primary radiation?

the beam produced at the tungsten target of the anode

what is secondary radiation?

the x-radiation created when the primary beam interacts with matter

what is scatter radiation?

an x-ray deflected form its path by interacting with matter

what is density?

the overall darkness of an image

what is contract?

how sharply dark and light areas differ on an image

what is impulse?

1/60 of a second; the unit used for exposure time

what is half-value layer?

the thickness of aluminum needed to reduce beam intensity by half

what is the tungsten filament?

the part of the machine that produces electrons when heated

what is the molybdenum cup?

the part of the machine that focuses electrons into a narrow beam aimed at the target

what is the tungsten target?

the part of the machine where electrons strike and x-rays are created

what is the copper stem?

the part of the machine that carries heat away from the target

what is the insulating oil?

the part of the machine that surrounds the tube and prevents overheating

what is the aluminum disk?

the part of the machine that filters out low-energy and long-wavelength x-rays

what is the lead collimator?

the part of the machine that restricts the size of the beam

what is the PID?

the part of the machine that aims and shapes the beam toward the patient

what is the step-down transformer?

the part of the machine that lowers voltage to 3-5 volts to heat the filament

what is the step-up transformer?

the part of the machine that raises voltage to 65,000-100,000 volts

what is the autotransformer?

the part of the machine that corrects minor fluctuations in line voltage

true/false: the shorter the wavelength an x-ray, the greater its penetrating power

true

true/false: secondary radiation is more penetrating the primary radiation

false: less

true/false: Compton scatter accounts for most of the scatter radiation produced during dental imaging

true

true/false: milliamgperage (mA) controls the quality, or penetrating power, of the x-ray beam

false: kilovoltage

true/false: increasing kilo voltage (kVp) increase the energy and penetrating power of the beam

true

true/false: increasing the kVp makes the image darker

false: lighter

true/false: a high-contrast image is useful for detection caries, and a low contrast image is useful for detecting periodontal disease

true

true/false: in an x-ray machine, electrons flow from the anode to the cathode

false: cathode to anode

true/false: less than 1% of the electrons energy at the target becomes x-rays; the rest becomes heat

true

true/false: if exposure time is increased, mA must be decreased to keep the same image density

true

true/false: changing from an 8-inch PID to a 16-inch PID makes the beam 4 times as intense

false: reduces by 1/4

true/false: the half-value layer is measured in millimeters of lead

false: aluminium

true/false: x-ray photons travel at the speed of light

true

true/false: an atom that loses an electron becomes a negative ion

false: postive

true/false: in the photoelectric effect, the photon hits an inner-shell electron and is completely absorbed

true

X-rays are created at the:

tungsten target of the anode

which interaction lets a photon pass through the patient unchanged and produces the densities on the image?

no interaction

when the target-to-receptor distance is doubled, the beam is:

¼ as intense

the current recommended kVp range for dental imaging is:

60-70 kVp

what kVp range produces a high-contrast image with many black and white areas?

65-70 kVp

the typical mA range used in dental imaging is:

7-15 mA

to keep image density the same, mA and exposure time have a(n):

inverse relationship

milliamperage controls ____, and kilovoltage controls _____?

the number of electrons formed; the force of electrons form cathode to anode

the half-value layer is measured with disks made of:

aluminum

an x-ray beam made of many different wavelengths is called:

polychromatic

when a unit is set at 70 kVp, the highest energy x-rays produced are:

70 keV

beam intensity is the combination of:

quality and quantity together

most x-rays produced at the target are:

braking (bremsstrahlung) radiation

which change makes an image darker (increases density)?

increasing exposure time

the distance from the x-ray source to the tooth is the:

target-object distance

what are the two particles found in the nucleus of an atom?

protons and neutrons

what are the two ways atoms combine to form molecules?

sharing of electrons and transferring of electrons

an atom gains an electron. what kind of ion does it become and why?

negative ion because it has more electrons than protons or neutrons

list the three parts of the xray tube:

• leaded glass housing

• cathode

• anode

what are the two components of the cathode?

tungsten filament and molybdenum cup

what are the two components of the anode?

tungsten target and copper steam

what is primary radiation?

produced at the tungsten target, exists at the tube head but doesn’t come into contact with matter yet

what is secondary radiation?

the beam left when primary radiant interacts with matter

what is scatter radiation?

a form of secondary radiation that deflects from its path and scatters in all directions by interacting with matter

what are the four possible interactions of x-radiaton with matter?

• no interaction

• absorption and photoelectric

• Compton scatter

• coherent scatter

what is the most common possible interaction of x-radation with matter?

Compton scatter

what is no interaction?

when radiation passes through the object (matter)

what is absorption effect?

all the energy from xray proton is transferred to the object and the xray photon ceases to exist

what is photoelectric effect?

ionization occurs (transfer of electrons) the xray photon crease to exist

what is compton scatter?

ionization of matter, photon loses some energy, photon continues in new direction

what is coherent scatter?

no changes to matter (object), but photon is scattered

what is density?

overall darkness of an image

what is contrast?

how sharply dark and light areas are separated on an image

how does increasing kVp affect beam quality?

increases quality

how does increasing kVp affect image density?

increase image density

how does increasing kVp affect image contrast?

decrease contrast

how does increasing mA affect the quantity of x-rays?

increases quantity

how does increasing mA affect the beam intensity?

increases intensity

how does increasing mA affect the image density?

increases density

how does increasing mA affect the quality of the beam?

no change

what is an impulse?

X-rays are created in a series of bursts

how many impulses are in a second?

60 impulses in 1 second

what is the inverse square law?

intensity is inversely proportional to the square of the distance from the source

if the PID changes from 60 inches to 8 inches, what happens to beam intensity?

it becomes 4 times more intense