Radiation Physics and X-ray Machine Flashcards
What is matter?
Anything that has mass and takes up space
What is the fundamental unit of matter?
Atom
What are the three components of an atom?
- Proton, in the nucleus
- Neutron, in the nucleus
- Electron, in electron orbits
What is the atomic number equal to?
Number of protons
What is the atomic mass equal to?
Number of protons plus the number of neutrons
How is the periodic table arranged?
According to atomic number
How do bonds form?
Transferring or sharing of electrons
Where do electrons revolve around the nucleus?
In orbitals or shells
How many electron shells are there?
7 shells max
What electron shell is closest to the nucleus?
K
What electron shell is farthest from the nucleus?
Q
What is binding energy?
Negative electrons are held in orbit by attraction to the positive nucleus
What is the binding energy dependent on?
Distance from nucleus
What shell has the highest binding energy?
K
What is binding energy measured in?
Electron volts or kilo electron volts
What is the ratio between protons and electrons in a neutral/stable atom?
Protons equal the number of electrons
What is ionization?
Removal of an electron from an atom
What is needed in order for ionization to occur?
Energy required to move the electron must exceed the binding energy of the electron
What is an ion pair?
Positive ion and ejected electron
What are the two types of radiation?
Particulate and electromagnetic
What is radiation?
Emission and propagation of energy through space
What type of radiation is electrons, alpha particles, protons, and neutrons?
Particulate radiation
What type of radiation are X-rays?
Electromagnetic radiation
What type of radiation is visible light?
Electromagnetic radiation
What are the three properties of electromagnetic radiation?
- Does not have mass
- Travel at the speed of light
- No electrical charge
What are the two properties of particulate radiation?
- Has mass
- Travel in straight lines at high speed
What type of radiation is a cathode ray?
Particulate radiation, high speed electrons originate at x-ray tube
What are the four types of non-ionizing radiation?
- Radio waves
- Microwaves
- Infrared
- Visible light
What are the three ionizing forms of radiation?
- Ultraviolet
- X-rays
- Gamma rays
What is radioactivity?
Process of unstable atoms undergo spontaneous disintegration or decay to try to be in a more balanced state
In dentistry, is radiation or radioactivity used?
Radiation, specifically X-rays
What is the filament in the cathode tube made of?
Tungsten
What does the filament sit in the cathode?
Focusing cup
What charge is a cathode?
Negative
Where are electrons produced?
Cathode
What is the function of the focusing cup?
Directs electrons in a narrow beam to the anode
What type of anode is used in dentistry?
Stationary
What charge is the anode? Why?
Positive to attract electrons
What is the focal spot of the anode made up of?
Tungsten
What is the stem made up of in the anode?
Copper
Is copper or tungsten a better heat conductor?
Copper
What surrounds the tube and transformers?
Insulating oil
What is the function of the insulating oil?
Prevent overheating by absorbing heat
Where is the transformers?
In the metal housing
What is the metal housing filled with?
Insulating oil
What is the function of the metal housing?
Protection of X-ray tube and grounds high voltage components
What is the function of the transformers?
Alters the voltage
What is the function of the tube head seal?
Permits the exit of x-rays
What is the tube head seal made of?
Lead and aluminum
What is the function of the aluminum disk?
Filter
What type of photons can penetrate through anatomic structures and each image receptors?
High energy photons
What do low energy photons cause?
Unnecessary exposure to the patient
How are low energy photons removed?
By adding filters
What are the inherent low energy photon filters?
- X ray tube housing
- Glass envelope
- Oil
What are the added low energy photon filters
Sheets of aluminum
What size aluminum filter is required for 50-70 kVp?
1.5 mm aluminum equivalent
What size aluminum filter is required for kVp above 70?
2.5mm aluminum equivalent
What is the collimator?
Lead plate with a hole that fits over the opening of the metal housing
What is the function of the collimator?
Restricts size of X-ray beam
What is the function of the PID?
Aims and shaped x-ray beam
What is the function of the step-down transformer?
Reduce voltage from 110-220 volts to 3-5 volts
All dental equipment is usually collimated to what diameter at the patient’s face?
2.75 inches, or 7cm
What is the function of the step-up transformer?
Increase voltage from 65,000 volts to 100,000 volts
What is autotransformer?
Voltage compensator that corrects minor fluctuations
What is the tube current?
Flow of electrons through the tube, from cathode to anode
What is the tube current controlled by?
mA
What is tube voltage controlled by?
kVp
High tube voltage is required between what structures to generate X-rays?
Cathode and anode
What is the function of the timer in the power supply?
Built to control the duration of x-ray exposure
What are the four steps that occur when the X-ray unit is turned on?
- Electricity is at 110 volts to 220 volts
- Step down transformer reduces it to 4 to 5 volts
- Heats the filament circuit, uses 3 to 5 volts
- Thermionic emission
What is thermionic emission?
Release of electrons from the outer shell of the tungsten filament
What are the three steps that occur when the exposure is activated?
- Step up transformer generates high voltage
- Electrons are produce at cathode, go to anode
- Reach the focal spot and the energy of the electrons is converted to x-ray photons
What happens to the heat produced during X-ray production?
Carried away by the copper stem and absorbed by the insulating oil
What two types of interactions occur when high energy electrons interact with the tungsten target?
- Breaking radiation
- Characteristic radiation
What type of interaction produces the most X-rays when high energy photons hit the tungsten target? How much?
Bremsstrahlung/breaking radiation, 70%
What happens during a direct hit interaction in breaking radiation?
Electron hits the nucleus and stops
What happens during a near miss interaction in breaking radiation?
Electron passes close to the nucleus
In both cases of breaking radiation, what is the energy of the electron converted into?
X ray photon
What type of interaction produces the least amount of X-rays when high energy photons hit the tungsten target? How much?
Characteristic radiation, 10-28%
What happens in characteristic radiation?
Incident electron ejects K shell electron, produces rebound electron, vacancy in K shell is filled by outer electron
What percentage of compton scattering interacts with the patient?
57%
What percentage of photoelectric absoportion interacts with the patient?
27%
What percentage of coherent scattering interacts with the patient?
7%
What percentage no interaction of radiation with patient occurs?
9%
In photoelectric interaction, the difference in energy between both shells is released as characteristic radiation, BUT…
Due to low energy, photons are absorbed into patient
Photoelectric interaction is needed to produce…
High contrast images in dental radiography
What is compton scattering?
X ray collides with outer shell electrons and ejects electrons from orbit, incident photon is scatter in a different direction with low energy
What is coherent scattering?
Interaction of low energy photons with whole atom, emits secondary x-ray photon that goes in different direction
Does coherent scattering contribute to diagnostic imaging?
No
What is X-ray beam quality?
Penetrating ability of X-ray beam
What is produced by shorter wavelength X-rays?
More energy, more penetration
What is produced by longer wavelength X-rays?
Low energy, less penetration
What controls quality and wavelength of X-ray beam
Tube voltage
Tube voltage makes electrons move from…
Cathode to anode
If you increase the kVp, what happens?
- Increase speed of electrons
- Electrons strike target with greater force
- Shorter wavelength
1 kV equals how many volts?
1000 volts
Dental radiography ranges in how many kilo-volts?
60 to 100 kV
What range of kilo-volts is over penetration?
80 to 100 kV
What range of kilo-volts does not allow for adequate penetration?
65-75 kV
If the X-ray unit was operating at 70 kVp, the tube will generate X-ray photons with energies ranging from maximum to…
70 keV
What is the X-ray beam quantity?
Number of x-rays produced in a dental x-ray unit
What does amperage determine?
Amount of electrons passing through the cathode filament
What does ampere measure?
Number of electrons or current flowing through the cathode filament
X-ray beam quantity relates to the…
Tube current
1 mA equals how many amperes?
1000
Does a change in mA equal a change in energy of electrons?
No
In dental radiography, how many mA is required?
7 to 15 mA
Exposure time determines…
Quantity
Milliamperes times exposure time equals…
mA
In order for the density to remain the same, if milliamperage is increased what must happen to the exposure time?
Exposure time must decrease
What is x-ray beam intensity?
Product of quality and quantity per unit area per time of exposure
How does higher kVp, mA, and exposure time affect the beam intensity?
Increases beam intensity
As x-rays travel from the source, their intensity…
Decreases
What does the inverse square law explain?
Relationship between distance and intensity
What does the inverse square law state?
Intensity of radiation is inverse proportional to the square distance from the source of radiation
The thickness of filters to reduce intensity by half is called what?
Half value layer
What factors impact exposure time?
- Seconds
- Impulses
What factor impact tube current?
mA
What factor impact tube voltage?
kVp
What impacts the quantity of X-rays produced?
- Exposure time
- Tube current
What impacts the quality of X-rays produced?
Tube voltage
Does kVp or mA impact quantity?
mAs
Does kVp or mA impact quality?
kVp
