WRONG FOLDER - ORPT - Radiation Physics and X-Ray Machine Flashcards
Matter
Anything that has mass and occupies space
Nucleus
Nucleons, protons and neutrons
Mass number
Number of protons and neutrons
Atomic number
Number of protons
Molecule
Two or more atoms joined by a chemical bond
Form by the transfer of electrons
Letters of orbital shells
K - Q
Farthest orbital shell is…
Q
Closest orbital shell is…
K
How are electrons held in orbits?
Electrons are negative, electrostatic attraction between the positive nucleus
What shell has the highest binding energy (BE)?
K
Binding energy is dependent on…
Distance from nucleus
What units of measure are used for binding energy (BE)?
Electron volts or kilo electron volts
Ionization
Removal of an electron from an atom
How does ionization work?
Energy required to remove the electron must exceed the BE of the electron
Ion pair
Positive ion and ejected electron
Radiation
Emission and travel of energy through space
Particulate radiation
- Electrons (beta particles, cathode rays), protons, neutrons, alpha particles
- Tiny particles of matter that has mass
- Travel in straight lines at high speed
Beta particles
Nucleus of radioactive atoms
Cathode rays
High speed electrons originated in an x-ray tube
Electromagnetic radiation
- Does not have mass or weight
- Travel at the speed of light
- No electrical charge
Examples of electromagnetic radiation
Visible light, x-rays, y-rays, UV, IR radiation/heat, microwaves, and radiowaves
How does electromagnetic radiation work?
Movement of wave-like energy as a combination of electric and magnetic fields
Non-ionizing radiation
Radiowaves, microwaves, infrared, visible light
Ionizing radiation
UV, x-rays, gamma rays
Radioactivity
- Process by which certain unstable atoms or elements undergo spontaneous disintegration to decay in an effort to station a more balanced nuclear state
- Throwing particles out to try to make itself more stable
Is radioactivity used in dentistry?
No
Electromagnetic radiation properties
- Does not have mass or weight
- No electrical charge
- Travel at the speed of light
What is a cathode made up of?
Made of coiled Tungsten wire filament
What is the source of electrons?
Cathode
What is the purpose of the focusing cup?
- Electrostatically focuses them in a straight path
- Electrons are then accelerated towards a positive anode
What is the charge of the cathode?
Negative
What is the focusing cup made up of?
Molybdenum
What happens when the cathode is heated?
The electron is produced at the cathode
What is the charge of an anode?
Positive
What is the source of x-rays
Anode
What is the anode made of?
Small tungsten target
What are the two types of anodes?
- Stationary
- Rotating: Not used in dental units
Where is the focal spot located?
- Anode
- 2-3mm thick
What is the focal spot made of?
- Copper
What conducts heat better?
Copper
Mental housing contains…
- Transformers
- Filled with insulating oil
Function of metal housing
- Protection of X-ray tube
- Grounds the high-voltage components
Transformer purpose
Alter the voltage
Insulating oil purposes
- Surrounding tube and transformers
- Prevents overheating by absorbing heat
Tube head seal purpose
Lead/aluminum covering of tube head that permits exit of x-rays
Aluminum disks purpose
- Acts as filter
- Absorbs low energy x-rays, reduces amount of radiation a person gets
Low energy photon receptors can’t…
Can not reach image receptors, end up cause unnecessary exposure to the patient
Higher energy photons can…
Penetrate through anatomic structures and reach image receptors or sensors
How are low energy photons removed?
Filter (small metallic disk)
Inherent filters on an X-ray machine
- Tube housing
- Glass envelope
- Oil
Required total filtration for 50-70 kVp
1.5mm Aluminum equivalent
Required total filtration for above 70kVp
2.5 mm Aluminum equivalent
Collimator
- Lead plate with a hole that fits directly over the opening of metal housing
- Restricts the size of X-ray beam, shapes it
Position indicating device (PID)
- Lead lined cylinder that extends from the metal housing of tube head
- Aims and shape the X-ray beam
Collimators purpose is to…
Regulate the shape and size of the beam
What size collimator is used in dental equipment?
2.75 inches or 7cm in diameter
What shape collimation reduces patient exposure?
Rectangle
Step down transformer
Reduce voltage of incoming line current 110-220V to 3-5 volts, filament circuit
Step up transformer
Increases the voltage to 65,000 to 100,000 voltage
Autotransformer
Voltage compensator that corrects minor fluctuations
Tube voltage
- High voltage is required between cathode and anode to generated X-rays
- Controlled by kVp
Tube current
- It is a flow of electrons through the tube
- From cathode to anode
- Controlled by mA
Timer
Built to control the duration of x-ray exposure
What happens when you turn the X-ray unit on?
- Electricity is 110-220 V
- Step down transformer reduces it to 4-5 V
- Heats the filament circuits, uses 3-5 V
- Thermionic emission
Thermionic emission
Release of electrons from the outer shell of tungsten filament
What happens when you activate the exposure?
- Step up transformer generates high voltage
- Electrons produced at cathode are accelerated towards anode. The focusing cup directs the electrons
- When they bombard the focal spot of the tungsten target, the K.E of electrons is converted into x-ray photons
- Ineffective!!!
Where does the heat go that is produced during the X-ray?
- Carried away from the copper stem
- Absorbed by insulating oil
Where are X-rays carried to?
travel through tube head seal, disks/filters, collimator, PID, then unleaded glass window
Bremsstrahlung or Breaking Radiation, direct hit interaction
Electron hits the nucleus and stops
Bremsstrahlung or Breaking Radiation, indirect interaction
Electron passes close to the nucleus
What happens in Breaking radiation?
K.E of electron is converted to X-ray photon
What interaction produces the most x-rays?
Breaking radiation, 70%
Characteristic radiation
- Incident electron with energy higher than BE of K-shell electron
- Ejects the K-shell electron
- Electron is replaced
In characteristic radiation, what fills the vacancy?
Outer shell electron
In characteristic radiation, the difference in energy between both shells is released as what?
X-ray photon
What percentage of x-rays are produced by characteristic radiation?
10-28%
No interaction of radiation with patient
9%
Absorption of photoelectric effect with patient
27%
Compton scatter with patient
57%
Coherent scatter with patient
7%
Incident photon
- Interacts with inner shell electrons of an atom in pt’s tissues,
- Gives off all energy and ceases to exist
If the energy is greater than the binding energy, the electron does what?
Absorbs energy and ejects as a photoelectron
During photoelectric interactions, where is there a vacancy? What fills it?
- K shell
- Outer shell electrons
In photoelectric interactions, the different in energy between both shells is released as…
- Characteristic radiation
- Is absorbed by patient because of low energy
Patient tissue atom accounts for…
28-30% of interactions
Compton Scattering
- X-ray photon collides with outer shell electrons and ejects election from orbit
- Incident photon is scattered into different direction with lower energy
When does compton scattering occur?
When an x-ray photon interacts with the outer orbital shell electrons
Compton scatter accounts for…
57% of interactions
In compton scattering, the incident photon collides with…
- The outer orbital electron of the patient’s tissue atom and is deflected from its path
- Scattered to a new direction as a scattered photon
Coherent scatter
Interaction of low energy x-ray photons (<10keV) with whole atom/outer shell electron
Coherent scatter causes…
Causes the atom to become excited for a moment at the same time frequency of the x-ray photon
In coherent scattering, what happens once the excited atom returns to it’s ground state?
- It emits a secondary x-ray photon with similar energy as the incident photon
- Secondary photon has a different direction than the incident photon
Coherent scattering accounts for…
7-8% of total x-ray interaction
What happens in coherent scattering?
Not enough energy to remove electron, vibrates whole atom, and goes into an excited state
Control panels
Predetermined setting for kVp, mA according to anatomic region of the mouth
X-ray beam quality
Mean energy or penetrating ability of x-ray beam
Shorter wavelength x-rays have…
- More energy
- More penetration
Longer wavelength x-rays have…
- Lower energy
- Less penetrating capability
Tube voltage controls…
Quality, wavelength, and energy
Tube voltage
Potential difference between cathode and anode that gives K.E. to electrons and make electrons move from cathode to anode
Can kVp be adjusted accordingly to individual patient needs?
Yes
Dental radiography kV are between
65-100kV
1kV equals how many V?
1000
Overpenetration is…
- 85-100kV
- Shorter wavelength, more energy
How many kV does not allow for adequate penetration
- 65 to 75 kV
- Longer wavelength, less energy
Higher kVp is used in areas where…
That are dense or thick
If the X-ray unit is operating at 70 kVp, x-ray photons with what energy ranges will be produced?
Max to 70keV
X-ray beam quantity
Number of x-rays produced in dental x-ray unit
Amperage determines…
Amount of electrons passing through the cathode filament
Ampere
Unit used to measure no of electrons or current flowing through the cathode filament
1mA equals how many amperes?
1000 amperes
1 milli ampere equals how many ampere?
1/1000
Does a change in mA equal a change in the K.E of electrons?
No
In dental radiography, how many mA is required?
7 to 15 mA
Exposure time
Time that x-rays are produced
Are x-rays produced in burst/pulses or a continuous stream?
Burst/pulses
The exposure time determines…
Quality
Milliamperes times exposure time equals…
mA
Inside x-ray tube voltage determines…
The speed with which electrons move
When milliamperage is increased the exposure time must what for the density to remain the same?
Decrease
When milliamperage is decreased the exposure time must do what for the density to remain the same?
Increase
X-ray beam intensity
Product of quality (energy of each photon), quantity (no of x ray photons), per unit area per unit time of exposure
Increase in intensity of x-ray beam means…
Higher kvP and exposure time
Distance between source of radiation and the film has an effect on the…
Intensity
What distances are considered?
- Source, teeth, and image receptor
As x-rays travel from the source their intensity…
Decreases
Inverse square law
Intensity of radiation is inversely proportional to the square distance from source of radiation
Aluminum filters remove…
Low energy
Half value layer
The thickness of the material which reduce intensity by half
What factors control mA and quantity of x-rays produced?
- Exposure time (seconds, time)
- Tube current (mA)
What factors control kVp and quality of x-rays produced
Tube voltage (kVp)
