Radiation Physics Flashcards
An x-ray is an ____ beam or photon of energy. ____
invisible
Image receptor is the material on which the ____ is created. This may be a film, fluoroscope, or a digital receptor. The receptor is processed (chemically or digitally), and a radiograph is made.
latent image
X-Ray Machine
X-Ray tube is positioned within the tube head with some components of the power supply
Tube may be ____ within the tube head to ____ the radiographic image quality
recessed
improve
Coolidge Tubes
Basic design introduced in ____ Composed of
-Anode
-Cathode – source of ____
-____ glass tube
Electrons from cathode strike ____, producing x-ray photons
1913
electrons
evacuated
anode
Coolidge Tubes
Requires power supply to:
Heat the ____ to generate electrons
Establish a ____ potential between the anode and the cathode to ____ the electrons
filament
high-voltage
accelerate
Cathode Features
____ – source of electrons within the x-ray tube
filament
Cathode
Filament (source of electrons)
Coil of ____ wire ____ long and ____
in diameter
Mounted on 2 ____ for support and carrying electric current
Wires connect to ____ and ____ voltage electric sources
____ of the wire causes the release of electrons (boiling off of electrons)
tungsten 1 cm 0.2 cm stiff wires high low incandescence
Focusing cup – ____ charged concave reflector (charge repels electrons)
negatively
Cathode
____ or ____ focusing cup – directs the electrons produced by the filament toward the ____ on the anode
Electrons travel from cathode to anode
by repellent forces on the ____ cathode and attractive forces on the ____ anode
nickel
molybdenum
focal spot
negatively charge
positively charged
Anode
____ embedded in ____ stem
Converts the kinetic energy of electrons from the filament into ____
Inefficient process – ____ of energy is lost as heat
tungsten target
copper stem
photon energy (x-rays)
99%
Tungsten (W)
High ____ (____)
Most efficient in producing x-rays
High \_\_\_\_ (\_\_\_\_0oC) Helps withstand the high temperatures produced during the generation of photons
High ____
Dissipates heat into the copper stem
Highest melting point of any ____
Low ____
Helps maintain the vacuum in the tube at high operating temperatures
atomic number 74 melting point 337 thermal conductivity metal vapor pressure
Tungsten Target
Embedded in a large block of ____ (a good thermal conductor)
Dissipates heat from the tungsten – reduces risk of target ____
____ surrounds the x-ray tube
Stationary anode
copper
melting
insulating oil
Focal Spot
Area on target where focusing cup ____ electrons from the filament
Sharpness of radiographic image ____ as the size of the focal spot ____
directs
increase
decreases
Focal Spot
Heat generated ____ as the size of the focal spot ____
Target is angled to ____ effective focal spot size while ____ distribution of electrons over a large target
Projection of focal spot is ____ to the electron beam (effective focal spot is ____ than the actual focal spot)
increases
decreases
decrease
maximizing
90 degrees
smaller
Production of X-rays
____ heats the filament of the cathode, releasing electrons – ____
Higher temperatures produce more ____
Electrons ____ from the cathode to the tungsten target on the anode
X-rays are produced as the electrons ____ or ____
current thermionic emission free electrons (electron cloud) accelerate decelerate stop
Electric Circuits
Electric current is the ____ of electrons through a conductor
Rate of flow (electrons/second past a set point) is measured in ____
Depends on ____ and ____ of the conductor to flow, measured in____
Ohm’s law: V = IR, V=potential, I=current, R=resistance
movement amperes voltage resistance ohms
Power Supply
Heats the filament using ____ current to generate electrons
Establishes a ____ between the anode and the cathode to ____ the electrons
low-voltage
high-voltage potential
accelerate
Power Supply(Electric Circuits)
 Tube ____ (mA) -Amperes are capitalized
Tube ____ (kVp) -Volts are capitalized
Together, mA and kVp determine the ____ of the x ray beam, along with the ____ and the ____ used
current voltage intensity target material filtration
Tube Current (mA)
Determines the ____ produced
The higher the mA, the greater the number of ____ generated, and consequently, more x rays produced
____ is the flow of electrons from the filament to the anode, then ____ to the filament through wiring of the power supply
number of electrons
electrons
tube current
back
Tube Current (mA)
Filament step-down transformer reduces voltage of the ____ to ~ ____
Controlled by the ____ , adjusting ____ and ____ through the low- voltage circuit
Regulates ____ of the filament and number of electrons ____
alternating current (AC) 10V mA switch resistance current temperature emitted
Tube Voltage (kVp)
Requires ____ between the anode and the cathode to generate x rays
____ converts the primary voltage from the input source to the ____ voltage
____ provides the high voltage required by the x-ray tube to accelerate electrons from the cathode to the anode
high voltage
autotransformer
secondary
high voltage transformer
Tube Voltage (kVp)
Peak voltage of the incoming line current is boosted to ____ kV
Boosts peak energy of the electrons to 60 to 100 keV
Line voltage is ____(alternating current), so intensity is greatest at peak of each ____ of the cycle
No x-rays are generated during the ____ portion
60 to 100
variable
positive portion
negative
Tube Voltage (kVp)
kVp determines the ____ of the electrons that generate the ____ from the target
kVp determines the ____ (quality) of the x rays produced
For tungsten targets, at least ____ must be used to produce the
____radiation
energy photons maximum energy 70 kVp k-characteristic
Half-Wave Rectification AKA \_\_\_\_ Limits x-ray production to \_\_\_\_ of the AC cycle Almost all dental x-ray units are \_\_\_\_
self-rectification
half
self-rectified
Filtration
Removes ____ photons (____ wavelength)
Accomplished with an ____ filter placed in the path of beam
Preferentially removes ____ photons
low energy
long
aluminum
low energy
Inherent Filtration
Consists of materials in ____ of the photon beam from the ____ to the point of ____ the x-ray head
These include
____ of the tube
____
____ surrounding oil
Ranges from ____ mm aluminum equivalent
path focal spot exiting glass wall insulating oil barrier 0.5 to 2.0 mm
Total Filtration
Sum of ____ and added ____ filtration
External filtration consists of ____ discs placed over the exit port of the tube head
Federal regulations require ____ aluminum equivalent for beams up to 70 kVp and ____ for beams over 70 kVp
inherent filtration external aluminum 1.5 mm 2.5mm
kV
increase >80
decrease 60-70
density:
increased (darker)
decreased (lighter)
contrast
low
hight
mA
increase
decrease
density:
increased (darker)
decreased (lighter)
contrast:
no effect
exposure time
increase
decrease
density:
increased (darker)
decreased (lighter)
contrast:
no effect
filter thickness
increase (thicker)
decrease (thinner)
density:
decreased
increased
contrast:
decreased
increased
target-detector distance
increase
decrease
density:
decreased
increased
contrast:
no effect
Control Panel Controls power supply to the tube head Controls number of \_\_\_\_ generated (the exposure time) Controls the \_\_\_\_ Controls the \_\_\_\_
impulses
kVp
mA
Tube rating and Duty Cycle
Tube rating: Maximum exposure time the tube can be energized without risk of damage to the target from ____.This should be posted at the ____
Duty Cycle: Frequency with which ____ can be made.
heat units(HU)= kVp x mA x sec dental diagnostic tubes < ____
overheating
machine
successive exposures
20 KHU
COHERENT SCATTERING (Classic/Thompson scatter) May occur when a low-energy incident photon (less than \_\_\_\_) passes near an outer electron of an atom (which has a low binding energy). The incident photon interacts with the electron by causing it to become momentarily excited at the same frequency as the incoming photon The incident photon ceases to exist. The excited electron then returns to the ground state and generates another x- ray photon with the same frequency and energy as in the incident beam. This interaction accounts for only about \_\_\_\_of the total number of interactions (per exposure) in a dental examination.
10 keV
8%
PHOTOELECTRIC ABSORPTION
Photoelectric absorption is critical in diagnostic imaging. This process occurs when an ____ photon collides with a ____ electron in an atom of the ____ medium. At this point the incident photon ceases to exist. The electron is ejected from its shell and becomes a ____ About ____ of the photons that are absorbed from a dental x-ray beam are absorbed by this process
incident bound absorbing recoil electron (photoelectron) 30%
COMPTON SCATTERING
Compton scattering occurs when a photon interacts with an ____ electron About ____ of the photons that are absorbed from a dental x-ray beam are absorbed by this process. In this interaction the incident photon collides with an ____, which receives kinetic energy and recoils from the point of impact. The path of the incident photon is deflected by its interaction and is scattered from the ____ of the collision.
outer orbital
62%
site
Roentgen [ Air Kerma=expressed as ____ that replaced ____]
Rad [ Absorbed dose 1 rad = 100 ergs/gram, 1 Gy = ____]
Rem [ Equivalent dose is absorbed dose averaged over tissue or organs and the radiation weighting factor]
Gray [ 1 Gy = ____]
Sievert [ 1 Sv = ____]
Kerma = ____ released in matter
Gy roentgen 100 rads 100 rads 100 rems kinetic energy
Effective dose (E) is used to estimate the risk in humans. It is the sum of the products of equivalent dose to each ____ or ____ and the ____:
E sum(WT X HT)
Unit of effective dose is the ____)
The tissue weighting factors include gonads, ____; red bone marrow, ____; esophagus, ____; thyroid, ____; skin, ____; and bone surface, ____
organ
tissue (Ht)
tissue weighting factor (Wt)
sievert (Sv)
- 20
- 12
- 05
- 05
- 01
- 01
Heat the filament longer > produce more e- > stronger ______
beam
two _____; three _____
circuits
transformers
If mA and kVp are fixed, you can alter the __________
exposure timing
HVL = _______ = _______
half value layer
aluminum
Collimators are usually made of ______
lead
