Unit 3 Flashcards
What is radiation?
the transmission of energy through waves or particles
can be ionizing or nonionizing
What are the 4 types of radiation?
Electromagnetic (EMR)
Particulate
Acoustic
Gravitational
What is electromagnetic radiation and how is it created?
charges have an electric field around them
moving charges create a magnetic field
disturbances in a charge create electromagnetic waves
How does electromagnetic radiation travel?
energy in a sinusoidal wave
the waves have no weight
EMR waves can interact with object as if they are particles
What is wave particle duality?
acts like a wave and a particle
What is the wave theory?
EMR affects both electrical and magnetic fields
fields are perpendicular to the direction of energy
What is amplitude?
maximum field strength
- higher amplitude = higher intensity
What is wavelength?
has the symbol lambda
distance between same points in the wave
- shorter wavelength = higher intensity
What is frequency?
cycles per second
measured in Hz
- higher frequency = higher intensity
what is a period?
how long each cycle takes
1/f
What is the formula for EMR waves in a vacuum?
c=f(lambda)
What is c?
the speed of light
c= 3 x 10^8 m/s
Memorize EMR spectrum
slide 11
What are the 4 types of wavelike interactions?
reflection
refraction
diffraction
interference
what is reflection?
bouncing off of an interface
what is refraction?
change in direction from change of speed
what is diffraction?
wave bounds around borders to create a pattern
what is interference?
waves can add together or cancel out
which wavelike interactions do x-rays do?
diffraction
what is quantum?
smallest unit of something
what is quantum of X-rays?
photons
we think of x-rays as distinct photons not as continuous waves
- particle like unit, but travels as a wave
Quantum theory equation?
each photon has a different amount of energy calculated by
E=hf
E = energy
f= frequency
h = Planck’s constant
What is ionization?
when radiation knocks e- of an atom making it a positive ion
what is excitation?
when an e- gains energy to go up a valance level
what are the particle like interactions?
ionization
excitation
flourescence
what is fluorescence?
immediate release of energy when electrons fill the lower shell again after an x-ray makes a space either by excitation or ionization
What are the properties of a low energy EMR vs high energy EMR?
Lower energy EMR tends to have more wave-like properties
Higher energy EMR tends to have more particle like properties
In the x-ray beam are the wavelengths of photons uniform?
no, beam is comprised ion many different wavelengths
The majority of the x-ray beam are _________ energy photons?
low
Max energy of a photon is determined by?
kVp
All photons have the same?
speed
For heat generation, where do most interactions occur?
between tube current electrons and outer shell electrons of Tungsten
What type of radiation is released in heat generation in the tube?
Infrared
What is the relationship between atomic number and binding energies?
proportional
Shells and binding energies of Tungsten?
Shell - # e- - Binding E (keV)
K - 2 - 69
L - 8 - 12
M - 18 - 3
N - 32 - 1
O - 12 - 0.1
P - 2 - negligible
What is characteristic radiation?
the ionization of Tungsten
Flourescence release the characteristic radiation - specifically talking about the K shell when talking about X-rays
This creates 0-10% of beam intensity
What is the Characteristic energy and how is it calculated? What is the characteristic energy of P to K of Tungsten?
difference in binding energies
69 - negligle = 69 keV
How much energy must an electron have to dislodge a tungsten electron?
at least 69.5 keV
under this would mean 0% of beam is characteristic (useful) radiation
Line graphs
also referred to as: discrete spectrum, line spectrum, homogenous spectrum, mono energetic spectrum
characteristic radiation only exits at certain levels
graphs show lines at each energy level
what kVp gives unto 10% useful radiation?
70 - 150 kVp
What does Bremen mean?
to brake/decelerate
What does Strahlung mean?
radiation
what is Bremsstrahlung radiation?
deceleration of electrons releases X-rays
How does Bremsstrahlung radiation occur?
electrons pass by positively charged nucleus and changes trajectory and slows down.
How do you create a max E photon Bremsstrahlung radiation?
needs to collide with nucleus and lose all kE in one go and all E become Xray photons
- rare interaction
Tungsten with Bremsstrahlung
high z
- very positive nucleus
attracts and slows electrons more
- increase KE lost
- increased E of photons
What are the different photon energies in a Bremsstrahlung beam?
Heterogenous
Continuous
Polyenergetic
where do most of the X-ray photons come from on the X-ray curve?
1/3 to 1/2 - more lower E photons
How is the intensity of the the beam calculated?
intensity = Energy/area/time
it is the area under the curve/line of the graph
What is intensity of the beam affected by?
energy of photons (quality)
photons per second (quantity)
what affects the quality of the characteristic radiation?
characteristic radiation only exists at set values
changing z changes energy levels
- the only thing that changes the energy of the photons is the element that they are made from via atomic number
what changes the quantity of characteristic radiation intensity?
increased kVp: increases amount of energy available to create photons
decreased ripple: more electrons have peak energy to make more photons
increased mA: more electrons to make photons
increased z: depends on k-shell binding energy kVp
what changes the quality of Bremsstrahlung radiation intensity?
increased kVp: increases peak energy of photons - increases average energy
decreased ripple: more electrons have peak energy and more E lost (good thing)
increased z: increases deceleration of electrons (good thing)
what is max energy?
highest energy photons possible
Depends on kVp
as far right as the Xray curve goes
What is low energy?
lowest energy photons
filtration
mostly Bremsstrahlung radiation
most likely to be filtered out - more filtration = less photons
L characteristic radiation would be low energy as well
average beam energy
effective beam energy
- affected by waveform, filtration, z
1/3 to 1/2 of peak
for average kVp multiply by 1/3 if crappy generator
1/2 is a better generator
line spectra
constant (distinct) energy levels
determined by z
height might change but not spot because it is fixed due to atomic number
study the emission spectra graphs
Slides 63-67
What is a quantum? How does this term relate to x-ray radiation?
Quantum is the smallest unit of something, this relates to the photons of x-ray radiation.
Compare the frequency, wavelength, and energy of a blue photon of light to a green photon of light?
The wavelength of blue photon is smaller than green photons of light, meaning the frequency and energy of blue photons are higher than the green photons of light.
Give examples of wavelength and particle-like behavior of EMR.
Wavelike behaviours tend to occur more in low energy EMR – diffraction, reflection, refraction and interference. Particle-like behaviours tend to occur more in high energy EMR – ionization, excitation and fluorescence.
What is the difference in the behavior between light photons and x-ray photons when they interact with mirrors or camera lenses? Why does this difference exist?
X-rays only diffract, where light diffracts, reflects, refracts and interferes.
What is the equation describing the relationship between wavelength and frequency of a photon? If an x-ray photon has a frequency of 2x1017 Hz, what would its wavelength be?
c=f(lambda)
(lambda) = c/f
Lambda = 3x10^8 m/s / 2x10^17 Hz
Lambda = 1.5x10^-9 m
Lambda = 1.5 nanometers
What is the equation describing the relationship between frequency and energy of a photon? What is the energy of the x-ray photon in the question above?
E=hf
E = (4.15x10^-15 eV*s) (2x10^17 Hz)
E = 830 eV
Describe the process of fluorescence and its applications in medical diagnostics.
Fluorescence is the release of energy when electrons drop down to fill a lower energy shell, its application is this is how x-ray photons are created.
Compare and contrast the characteristics of high-energy and low-energy photons.
High energy photons have short wavelength, high frequency and are more penetrating (more particle like properties). low energy photons have long wavelength, low frequency, less penetrating and is more harmful (more wave like properties)
Describe the following two x-ray production processes, including the interactions that occur, how likely they are to occur, and the possible energies of the photons produced:
a. Characteristic radiation
An incoming electron knocks out an inner-shell electron, creating a vacancy. An outer shell electron fills the gap, emitting an X-ray photon with energy equal to the difference between the binding energy between the shells. It is less likely than bremsstrahlung radiation, higher probability with high atomic number elements.
b. Bremsstrahlung radiation
An incoming electron is deflected by the nucleus of a target atom, loses energy and emits an X-ray photon. More likely than characteristic radiation; probability increases with their atomic number and electron energy. Photon energy is in a continuous range from near zero up to the maximum energy of the incoming electron.
- Using the diagram below, what would the emitted energies be for a transition from O to K-shell and from N to K-shell in a tungsten atom? Why are these referred to as characteristic radiation?
O to K - 68.9 kEv
N to K – 68 kEv
These X-ray emissions are called characteristic radiation because they are unique to the specific element. When an electron from an outer shell fills a vacancy in the inner shell.
How would the energy levels emitted be different if the above element was aluminum?
They would be different because the binding energies would be different.
How does kinetic energy of the tube current affect the production of characteristic radiation? Would more characteristic photons be produced if there was more kinetic energy? Would the energy of the photons change?
Kinetic energy of the tube current affects the energy of the electrons to knock out the inner shell electrons, resulting in more characteristic radiation being produced, however, there would be no change in the photon energy.
Describe the interaction that creates a maximum energy photon.
Maximum energy photons are created when an electron jumps from P shell to K shell of Tungsten.
Why do the electrons in the tube current more commonly produce many low energy photons instead of one high energy one?
Electrons are deflected multiple times by atoms, each time losing a small amount of energy, the loss occurs gradually over many interactions, resulting in lower-energy photons. It is rare for the interactions in which an electron collides directly with the nucleus.
Why is the k-characteristic radiation of tungsten the only one that appears in the x-ray beam?
It is the only shell with binding energy high enough to make characteristic radiation to become an X-ray beam.
The tube current is accelerated towards the anode with a 100kVp potential difference. What is the max energy of the generated x-rays? What is the range of x-ray photons produced? What is the most likely range of the average energy of the beam?
Max energy of the generated X-rays are 100 keV. The range of X-ray photons produced range from 0keV to 100keV. Most likely average energy is 30-50keV.
What is meant by the following terms: continuous, line, discrete, homogeneous, and heterogeneous.
Continuous – Bremsstrahlung radiation, line – characteristic radiation, discrete – characteristic radiation, homogenous – have uniform energy distribution, heterogenous – bremsstrahlung and characteristic, most x-ray tubes produce these.
What is the relationship between kVp and bremsstrahlung radiation?
kVp determines the max energy of bremsstrahlung radiation.
If we doubled our kVp from 50 to 100, what changes would occur in the beam? Which beam would have the most penetrating? Which beam would have the most harmful photons?
It would become more penetrating and would have more harmful photons.
How does kV waveform affect the kinetic energy of the tube current? How does this affect the x-ray beam spectrum?
The kV waveform determines how consistently the electrons are accelerated and how high their kinetic energy reaches at any given time.
What features of the beam spectrum would change if you increased the z of the target? How would they change?
If you increase Z of the target, increased intensity of the X-ray beam would occur.
How does mA affect the production of x-rays?
Increasing mA can create more electrons to make more x-ray photons.
How does filtration affect the intensity and energy of the beam spectrum?
Filtration filters out the low energy photons of the beam spectrum.
Which beam, an unfiltered or a filtered one, would require the greatest mAs to produce the necessary amount of radiation? Which would cause the greatest dose?
Greater mAs would be required for the unfiltered beam to create the same amount of useful radiation. The unfiltered beam would also create the greatest patient dose.
What image qualities are affected by the shape of the beam spectrum?
Image contrast, sharpness/resolution, dose, brightness/density and penetration/tissue differentiation.
