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
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?
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.
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 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
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.
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. 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.
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!