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Electromagnetic Radiation. RTEC 111 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
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Electromagnetic Radiation RTEC 111 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
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
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?
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 107to 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
RadiofrequencyMRI 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 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 RadiationX-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 • 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 Distance #2 - Squared Intensity #1 Distance #1 - Squared Intensity #2
