Electromagnetic Radiation Electricity RTEC 111 Objectives n Properties

Electromagnetic Radiation & Electricity RTEC 111

Objectives n Properties of photons n Visible light, radiofrequency & ionizing radiation n Wave-particle duality of EM radiation n Inverse square law n Electricity

X-ray photons n X-rays and light are examples of electromagnetic photons or energy n EM energy exists over a wide range called an “energy continuum” n The only section of the EM continuum apparent to us is the visible light segment

Visible light

Photon n Is the smallest quantity of an type of EM radiation. (atom is the smallest element) n A photon may be pictured as a small bundle of energy or quantum, traveling through space at the speed of light n Properties of photons include frequency, wavelength, velocity, and amplitude

AMPLITUDE, WAVELENGTH, SPEED, VELOCITY, FREQUENCY

Photons n All EM photons are energy disturbances moving through space at the speed of light n Photons have no mass or identifiable form n They do have electric and magnetic fields that are continuously changing

Photons – variations of amplitude over time n Photons travel in a wave-like fashion called a sine wave n Amplitude is one half the range from crest to valley over which the sine wave varies

Velocity n When dealing with EM radiation all such radiation travels with the same velocity n X-rays are created at the speed of light and either exist with the same velocity or do not exist at all

Frequency n The rate of the rise and fall of the photon is frequency n Oscillations per second or cycles per sec n Photon energy is directly proportional to its frequency n Measured in hertz (Hz) n 1 Hz = 1 cycle per second

Frequency n the # of crests or the # of valleys that pass a point of observation per second.

Wavelength n The distance from one crest to another, from one valley to another

Describing EM Radiation n Three wave parameters; velocity, frequency, and wavelength are needed to describe EM radiation n A change in one affects the value of the other n Which value remains constant for x- rays?

Wavelength Equation

Just to keep it simple n For EM radiation, frequency and wavelength are inversely proportional

Electromagnetic Spectrum n Frequency ranges from 102 to 1024 n Wavelengths range from 107 to 10 -16 n Important for Rad Techs: visible light, x- radiation, gamma radiation & radiofrequency

Visible light: Important for processing, intensifying screens, viewing images and fluoroscopy image n Smallest segment of the EM spectrum n The only segment we can sense directly n White light is composed of photons that vary in wavelengths, 400 nm to 700 nm

Sunlight n Also contains two types of invisible light: infrared and ultraviolet

Radiofrequency MRI uses RF & Magnets n RF waves have very low energy and very long wavelengths

Ionizing Radiation n Contain considerably more energy than visible light photons or an RF photon n Frequency of x-radiation is much higher and the wavelength is much shorter n When we set a 80 k. Vp, the x-rays produced contain energies varying from 0 to 80 ke. V.

X-ray vs Gamma rays n What is the difference?

Wave – particle duality n A photon of x-radiation and a photon of visible light are fundamentally the same n X-rays have much higher frequency, and hence a shorter wavelength than visible light

Visible light vs X-ray

Visible light vs X-ray n Visible light photons tend to behave more like waves than particles n X-ray photons behave more like particles than waves.

Wave-particle duality - Photons n Both types of photons exhibit both types of behavior n 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 n Light interacting with matter n Reflected n Transmitted n Attenuated n Absorbed

Characteristics of Radiation X-rays interacting with matter n Scatter n Transmitted n Attenuated n Absorbed n Radiopaque n Radiolucent

Energy interaction with matter n Classical physics, matter can be neither created nor destroyed n Law of conservation of matter n Energy can be neither created nor destroyed n Law of conservation of energy

Inverse Square Law n When radiation is emitted from a source the intensity decreases rapidly with distance from the source n 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 n Applies basic rules of geometry n The intensity of radiation at a given distance from the point source is inversely proportional to the square of the distance. n 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 n Convert electric energy to electromagnet energy. n A well controlled electrical current is applied and converted to mostly heat and a few xrays.

Atom construction n Because of electron binding energy, valence e- often are free to travel from the outermost shell of one atom to another. n What do we know about e- binding energy of an atom?

Electrostatic Laws n Electrostatic force n Unlike charges attract; like charges repel n Electrostatic force is very strong when objects are close but decrease rapidly as objects separate. n Electrostatic force has an inverse square relationship. Where else do we apply the inverse square relationship with intensity?

Electric Potential n Electric charges have potential energy. When positioned close to each other. E- bunched up at the end of a wire have electric potential energy. n Electric potential is sometimes called voltage, the higher the voltage, the greater potential.

Electric Circuit n X-ray systems require complicated electric circuits for operation. n Circuit symbols and functions. Pg. 80

Electric current n Electricity = the flow of electrons along a conductor. n E- travel along a conductor in two ways. Alternating current (AC) - sine wave n Direct current (DC) n n X-ray imaging systems require 20 to 150 k. W of electric power.

More on x-ray circuitry to come later… • What questions do you have? • No excuses especially for x-ray students!