Transcript Electromagnetic Radiation

Electromagnetic
Radiation
Bushong Ch. 4
Objectives
 Properties of photons
 Visible light, radiofrequency & ionizing
radiation
 Wave-particle duality of EM radiation
 Inverse square law
 Electricity
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
Visible light
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
AMPLITUDE, WAVELENGTH,
SPEED, VELOCITY, FREQUENCY
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
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
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
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
Frequency
 the # of
crests
or the # of
valleys that
pass a point
of observation
per second.
Wavelength
 The distance
from one crest to
another, from
one valley to
another
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?
Wavelength
Equation
Just to keep it simple
 For EM radiation, frequency and
wavelength are inversely proportional
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
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
Sunlight
 Also contains two types of invisible light:
infrared and ultraviolet
Radiofrequency
MRI uses RF & Magnets
 RF waves have very low energy and very
long wavelengths
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.
X-ray vs Gamma rays
 What is the difference?
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
Visible light vs X-ray
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.
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.
Characteristics of Radiation
Visible light
 Light interacting with matter
 Reflected
 Transmitted
 Attenuated
 Absorbed
Characteristics of Radiation
X-rays
 X-rays interacting with matter
 Scatter
 Transmitted
 Attenuated
 Absorbed
 Radiopaque
 Radiolucent
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
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
Inverse Square Law Formula
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.
Inverse Square Law Formula
Intensity #1
Intensity #2
Distance #2 Squared
Distance #1 Squared
Inverse Square Law
Intensity Is Spread Out
Questions?
Electricity
RTEC 111
Bushong Ch. 5
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 xrays.
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?
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?
Electric Potential
 Electric charges have potential energy.
When positioned close to each other. Ebunched up at the end of a wire have electric
potential energy.
 Electric potential is sometimes called voltage,
the higher the voltage, the greater potential.
Electric Circuit
 X-ray systems require complicated electric
circuits for operation.
 Circuit symbols and functions. Pg. 80
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.
More on x-ray circuitry to come
later…
• What questions
do you have?
• No excuses
especially for x-ray
students!