Chapter 3 Electromagnetic and Particulate Radiation PDF

Chapter 3 Electromagnetic and Particulate Radiation  Electromagnetic Radiation  James Maxwell – 19th century  All electromagnetic radiation – no mass, no charge, carries energy in waves as electric and magnetic disturbances, travels at speed of light  Electromagnetic Ra...

Chapter 3 Electromagnetic and Particulate Radiation  Electromagnetic Radiation  James Maxwell – 19th century  All electromagnetic radiation – no mass, no charge, carries energy in waves as electric and magnetic disturbances, travels at speed of light  Electromagnetic Radiation: Nature and Characteristics  Electromagnetic spectrum: a way of ordering or grouping the different electromagnetic radiations  Have the same velocity (the speed of light (c) = 3  108 m/s)  Vary only in their energy, wavelength, and frequency  Electromagnetic Radiation: Nature and Characteristics  Members of the electromagnetic spectrum from lowest energy to highest: radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays  Wavelengths range from 106 to 10-16 meters (m)  Frequencies range from 102 to 1024 hertz (Hz)  Electromagnetic Radiation: Nature and Characteristics  The range of energy, frequency, and wavelength of the electromagnetic spectrum is continuous.  Electromagnetic Radiation: Nature and Characteristics  Electromagnetic radiation  Is a form of energy that originates from the atom When changes in the atom occur:  Electrons change orbital position  Atomic nuclei emit excess energy to regain stability  Can exist apart from matter  Can travel through a vacuum  Electromagnetic Radiation: Energy  Energy and frequency of electromagnetic radiation are related mathematically  The energy can be calculated: E = hf  h is Planck’s constant, 4.135 x 10-15 eVs; 6.626 x 10-34 Js  Describes relationship between energy and frequency  Energy ranges from 10-12 to 1010 electron volts (eV)  Electromagnetic Radiation: Wave-Particle Duality  Electromagnetic radiation exhibits properties of a wave or a particle depending on its energy and in some cases its environment.  This is called wave-particle duality. Wave Characteristics  Wavelength  The relationship between wavelength and frequency is inverse  Wavelength is generally expressed in meters (m).  The actual measure is typically in exponential form (e.g., 10 -11 m).  Frequency  Frequency is generally expressed in hertz (Hz).  Frequencies that are very large or very small and are expressed in exponential form (e.g., 1019 Hz). Electromagnetic Spectrum  Wave Formula  Velocity = frequency × wavelength (v = fλ)  All electromagnetic energy travels at speed of light, so replace velocity with c  c = fλ  Solving for frequency (f = c/λ)  Solving for wavelength (λ = c/f)  Electromagnetic Radiation  Can also be characterized by how it interacts with matter  High energy photons act more like particles (x- rays and gamma rays)  Low energy more like waves (radio, micro)  Inverse Square Law  The intensity (I) of electromagnetic radiation diminishes over distance (d).  X-rays and Gamma Rays  Because of their high energy they exhibit more particulate characteristics.  They can burn skin.  Intensity varies according to the inverse square law  Can ionize matter Removal of an electron from an atom – ionization Becomes ion pair Can damage cell molecules and DNA  X-rays and Gamma Rays  X-rays and gamma rays originate from different energy sources.  Gamma rays originate in the nuclei of atoms and represent the excess energy the atom is giving off to reach a stable state.  X-rays originate through interactions between electrons and atoms.  The Rest of the Spectrum  Radio waves  At the low end of the energy spectrum  Commonly used in magnetic resonance imaging  Do not ionize atoms  Microwaves  Commonly used to transmit cell phone signals and heat food  Do not ionize atoms, causes vibration of atoms and molecules The Rest of the Spectrum  Infrared light  Sometimes used to “beam” information between electronic devices  Does not ionize atoms  Visible light  Represents the colors we see in the world around us  It is a tiny portion of the electromagnetic spectrum  Does not ionize atoms  Color we see is the color reflected (the object is absorbing every color except what you see)  The Rest of the Spectrum  Ultraviolet light  Has energies approaching those of x-rays and gamma rays  Commonly used in tanning beds  Can be harmful  Stimulates melanin production in skin cells, which is damaging to the melanocytes  Does not ionize atoms Summary of Electromagnetic Spectrum Ionize Electromagnet Common Use Matter ic Radiation ? Radio waves Broadcasting of music, MRI No Microwaves Cell phone signals, microwave ovens No Communication between electronic Infrared light No devices The part of the spectrum the human Visible light No eye perceives as colors Ultraviolet light Tanning beds No X-rays Medical imaging, radiation therapy Yes Nuclear medicine imaging, radiation Gamma rays Yes therapy  Particulate Radiation  Particulate radiation (alpha particles and beta particles)  Have the energy to ionize matter  More often dealt with in nuclear medicine and radiation therapy  Particulate Radiation  Radioactivity  Radioactivity - the process by which an atom with excess energy in its nucleus emits particles and energy to regain stability, known as radioactive decay.  Elements that are composed of atoms with unstable nuclei are said to be radioactive.  Some in nature (radium and uranium), others artificially produced (technetium)  Particulate Radiation  A radioactive substance does not suddenly decay all at once; it may last minutes or billions of years.  A half-life is the length of time it takes for half the remaining atoms in an amount of the element to decay.  Particulate Radiation  Alpha particles  Are two protons bound to two neutrons  Have a net positive charge  Have a short range  Are relatively large and cannot penetrate most objects (penetrate about 0.1 mm)  Uranium 238-when decays, it emits an alpha particle  Particulate Radiation  Beta particles  Are electrons that are emitted from unstable nuclei  Do not originate in an electron shell  Are lighter and smaller than an alpha particle  May ionize atoms along their path  Penetrate up to 2 cm  Particulate Radiation  Beta particles may have a positive or negative charge.  The negatively charged beta particle (negatron) differs from an electron only in that it originated in the nucleus of the atom.  The positively charged beta particle (positron) is called a positron.  When beta particles are stopped by collisions with other atoms, they join with atoms just as electrons do.  Sources of Exposure  Humans are exposed to ionizing radiation every day.  Natural/background and manmade  Further divided into cosmic, terrestrial, internal, and medical.  Total dose from these sources vary according to geographic location.