electromagnetic radiation & electricity rtec 111
TRANSCRIPT
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Electromagnetic Radiation & Electricity
RTEC 111
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Objectives
Properties of photons
Visible light, radiofrequency & ionizing
radiation
Wave-particle duality of EM radiation
Inverse square law
Electricity
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X-ray photons
X-rays and light are examples of electromagnetic photons or energy
EM energy exists over a wide range called an “energy continuum”
The only section of the EM continuum apparent to us is the visible light segment
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Visible light
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Photon
Is the smallest quantity of an type of EM radiation. (atom is the smallest element)
A photon may be pictured as a small bundle of energy or quantum, traveling through space at the speed of light
Properties of photons include frequency, wavelength, velocity, and amplitude
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AMPLITUDE, WAVELENGTH, SPEED, VELOCITY, FREQUENCY
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Photons
All EM photons are energy disturbances moving through space at the speed of light
Photons have no mass or identifiable form
They do have electric and magnetic fields that are continuously changing
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Photons – variations of amplitude over time Photons travel in a wave-like fashion called a
sine wave
Amplitude is one
half the range from
crest to valley
over which the sine
wave varies
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Velocity
When dealing with EM radiation all such radiation travels with the same velocity
X-rays are created at the speed of light and either exist with the same velocity or do not exist at all
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Frequency
The rate of the rise and fall of the photon is frequency
Oscillations per second or cycles per sec
Photon energy is directly proportional to its frequency
Measured in hertz (Hz) 1 Hz = 1 cycle per second
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Frequency
the # of
crests
or the # of
valleys that
pass a point
of observation
per second.
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Wavelength
The distance
from one crest to
another, from
one valley to
another
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Describing EM Radiation
Three wave parameters; velocity, frequency, and wavelength are needed to describe EM radiation
A change in one affects the value of the other
Which value remains constant for x-rays?
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WavelengthEquation
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Just to keep it simple
For EM radiation, frequency and wavelength are inversely proportional
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Electromagnetic Spectrum
Frequency ranges from 102 to 1024
Wavelengths range from 107 to 10-16
Important for Rad Techs: visible light, x-radiation, gamma radiation & radiofrequency
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Visible light: Important for processing, intensifying screens, viewing images and fluoroscopy image
Smallest segment of the EM spectrum The only segment we can sense directly White light is composed of photons that vary
in wavelengths, 400 nm to 700nm
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Sunlight
Also contains two types of invisible light: infrared and ultraviolet
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RadiofrequencyMRI uses RF & Magnets RF waves have very low energy and very
long wavelengths
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Ionizing Radiation
Contain considerably more energy than visible light photons or an RF photon
Frequency of x-radiation is much higher and the wavelength is much shorter
When we set a 80 kVp, the x-rays produced contain energies varying from 0 to 80 keV.
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X-ray vs Gamma rays
What is the difference?
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Wave – particle duality
A photon of x-radiation and a photon of visible light are fundamentally the same
X-rays have much higher frequency, and hence a shorter wavelength than visible light
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Visible light vs X-ray
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Visible light vs X-ray
Visible light photons tend to behave more like waves than particles
X-ray photons behave more like particles than waves.
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Wave-particle duality - Photons
Both types of photons exhibit both types of behavior
EM energy displays particle-like behavior, and sometimes it acts like a wave; it all depends on what sort of experiment you're doing. This is known as wave/particle duality, and, like it or not, physicists have just been forced to accept it.
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Characteristics of RadiationVisible light
Light interacting with matterReflectedTransmittedAttenuatedAbsorbed
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Characteristics of RadiationX-rays
X-rays interacting with matterScatterTransmittedAttenuatedAbsorbed
RadiopaqueRadiolucent
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Energy interaction with matter
Classical physics, matter can be neither created nor destroyedLaw of conservation of matter
Energy can be neither created nor destroyedLaw of conservation of energy
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Inverse Square Law
When radiation is emitted from a source the intensity decreases rapidly with distance from the source
The decrease in intensity is inversely proportional to the square of the distance of the object from the source
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Inverse Square Law Formula
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Inverse Square Law
Applies basic rules of geometry
The intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance.
Doubling the distance decreases intensity by a factor of four.
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Inverse Square Law Formula
Intensity #1
Intensity #2
Distance #2 - Squared
Distance #1 - Squared
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Inverse Square Law
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Intensity Is Spread OutIntensity Is Spread Out
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Questions?Questions?
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Electricity
RTEC 111
Bushong Ch. 5
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X-ray imaging system
Convert electric energy to electromagnet energy.
A well controlled electrical current is applied and converted to mostly heat and a few x-rays.
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Atom construction
Because of electron binding energy, valence e- often are free to travel from the outermost shell of one atom to another.
What do we know about e- binding energy of an atom?
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Electrostatic Laws
Electrostatic force Unlike charges attract; like charges repel
Electrostatic force is very strong when objects are close but decrease rapidly as objects separate. Electrostatic force has an inverse square
relationship. Where else do we apply the inverse square relationship with intensity?
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Electric Potential
Electric charges have potential energy. When positioned close to each other. E- bunched up at the end of a wire have electric potential energy.
Electric potential is sometimes called voltage, the higher the voltage, the greater potential.
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Electric Circuit
X-ray systems require complicated electric circuits for operation.
Circuit symbols and functions. Pg. 80
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Electric current
Electricity = the flow of electrons along a conductor.
E- travel along a conductor in two ways. Alternating current (AC) - sine wave Direct current (DC)
X-ray imaging systems require 20 to 150 kW of electric power.
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More on x-ray circuitry to come later…
• What questions
do you have?
• No excuses
especially for x-ray
students!