Electromagnetic Radiation

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Electromagnetic Radiation

• RTEC 111
• Bushong Ch. 4

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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 Radiation Visible light

• Light interacting with matter
• Reflected
• Transmitted
• Attenuated
• Absorbed

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Characteristics of Radiation X-rays

• X-rays interacting with matter
• Scatter
• Transmitted
• Attenuated
• Absorbed
• Radiopaque
• Radiolucent

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Energy interaction with matter

• Classical physics, matter can be neither created
  nor destroyed
• Law of conservation of matter
• Energy can be neither created nor destroyed
• Law 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
Distance 2 - Squared
Intensity 1
Distance 1 - Squared
Intensity 2
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Inverse Square Law
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Intensity Is Spread Out
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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.
• Pg. 82

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More on x-ray circuitry to come later

• What questions
• do you have?
• No excuses
• especially for x-ray
• students!