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PHYSICS FOR RADIOGRAPHERS 2 (HDR202) CHAPTER 2: Electromagnetic Radiation PREPARED BY: MR KAMARUL AMIN BIN ABDULLAH SCHOOL OF MEDICAL IMAGING FACULTY OF HEALTH SCIENCES CHAPTER 2: ELECTROMAGNETIC RADIATION LEARNING OUTCOMES TOPIC At the end of the lesson, the student should be able to:- Define what is electromagnetic radiation, characteristic of radiation, and velocity and wave. Explain what is electromagnetic spectrum in which related to wave and color spectrum. Differentiate between ionizing radiation and non ionizing radiation. Explain what is quantum duality. Explain how is the propagation of the wave and energy. Slide 2 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION TOPIC OUTLINES TOPIC INTRODUCTION 2.1 Photons 2.3 Wave-Particle Duality 2.1.1 Velocity and Amplitude 2.3.1 Wave Model: Visible Light 2.1.2 Frequency and Wavelength 2.3.2 Inverse Square Law 2.1.3 Mathematical Formula 2.3.3 Particle Model: Quantum Theory 2.2 Electromagnetic Spectrum 2.4 Propagation of EMR 2.2.1Types of EM Radiation 2.2.2 Relevant in Medical Imaging 2.5 Inverse Square Law 2.6 References Slide 3 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION INTRODUCTION TOPIC Electromagnetic radiation are transverse waves, similar to water waves in the ocean or the waves seen on a guitar string. This is as opposed to the compression waves of sound. EM radiation have photons that can be described by sine waves. They have amplitude, wavelength, velocity and frequency which cause the waves to affect matter differently. Slide 4 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC Photons firstly were described by ancient Greek and remains till today. Photons are known as electromagnetic energy. Examples: x-rays, visible light and radiofrequencies. A photon is the smaller quantity of any type of EM energy. It may be pictured as a small bundle of energy, sometimes called quantum that travels through space at the speed of light. An x-ray photon is a quantum of electromagnetic energy. Slide 5 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC Crest: The highest point of the wave Trough: The lowest point of the wave Amplitude: Height of the wave as measured between the trough and the crest Wavelength: The distance between two identical points on the wave Period: The time it takes for a wavelength to pass a stationary point Frequency: The number of oscillations completed per second Unit Hz or s-1 Slide 6 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC 2.1.1 Velocity and Amplitude Photons are energy disturbances that move through space at the speed of light (c). The velocity of all electromagnetic radiation is 3 x 108 m/s. Photons have no mass but they have electric and magnetic fields that can be shown by sine wave. Sine waves can be described by mathematical formula and simplistically, it is the variations of amplitude over time. Amplitude is one-half the range from crest to valley over which the sine wave varies. Slide 7 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC 2.1.2 Frequency and Wavelength Sine waves describes variations in the electric and magnetic fields as photon travels with velocity (c). The important properties of this are frequency (f) and wavelength () Frequency: the number of oscillations (cycle) of the electromagnetic field per unit time. i.e.: the number of crests or valleys pass the point per unit of time. Wavelength: The distance between corresponding points on two successive waves. i.e: the distance from one crest to another, from one valley to another, from any point on the sine wave to the next corresponding point. Slide 8 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC Sine waves are associated with many naturally occurring phenomena in addition to electromagnetic energy. Slide 9 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC 2.1.3 Mathematical Formula The Wave Equation Wavelength = Velocity/Frequency or v = f Electromagnetic Wave Equation c=f Electromagnetic Wave Equation F=c/ or = c/f Slide 10 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.1 Photons TOPIC Relationships among velocity (v), frequency (f), and wavelength for any sine wave. Slide 11 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC A wide range of values such as frequency and wavelength covers many types of EM radiation. Grouped together, these types of energy make up the electromagnetic spectrum. Electromagnetic spectrum includes the entire range of electromagnetic radiation. The known EM spectrum has three regions most important to radiologic science: visible light, x-radiation, and radiofrequency. Other portions of spectrum include UV light, infrared light, and microwave radiation. Slide 12 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC This chart shows the value of energy, frequency, and wavelength and identifies the three imaging windows. Slide 13 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1 Types of Electromagnetic Radiation 2.2.1.1 Radio Waves RW covers a considerable portion of the EM spectrum. The lowest energy EM radiation. Radio waves have the longest wavelengths in the electromagnetic spectrum which is 1 mile (1.5 kilometer) or more. It has many uses such as bring music to your radio, carry signals for your television and cellular phones. Slide 14 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC Slide 15 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1.2 Microwaves Microwaves have wavelengths that can be measured in centimeters. Microwaves have many uses, such as to transmit information from one place to another (telephone calls, computer data), remote sensing, doppler radar (weather forecasts), and food heating. It has higher frequency and energy than radio waves but shorter wavelength. Slide 16 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC Slide 17 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1.3 Infrared Light (IR) Infrared light lies between the visible and microwave portions of the electromagnetic spectrum. Infrared light has a range of wavelengths, just like visible light has wavelengths that range from red light to violet. "Near infrared" light is closest in wavelength to visible light and “Far infrared" is closer to the microwave region of the electromagnetic spectrum. Slide 18 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC Far infrared waves are thermal. The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared. Near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's remote control. The primary source of infrared radiation is heat or thermal radiation, any object which has a temperature radiates in the infrared. Slide 19 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1.4 Visible Light Visible light occupies the smallest segment of the EM spectrum, and yet it is the only portion that we can sense directly. We sense these waves as the colors of the rainbow. Each color has a different wavelength. Red has the longest wavelength and violet has the shortest wavelength. When all the waves are seen together, they make white light. Their wavelengths are in the range of 1/1000 centimeter. Slide 20 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC When white light shines through a prism, the white light is broken apart into the colors of the visible light spectrum. Water vapor in the atmosphere can also break apart wavelengths creating a rainbow. Slide 21 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1.5 Ultraviolet Radiation (UV) Ultraviolet light is located in the EM spectrum between visible light and ionizing radiation. Ultraviolet (UV) light has shorter wavelengths than visible light. It can be classified into three parts. The three parts are distinguished by how energetic the ultraviolet radiation is, and by the "wavelength" of the ultraviolet light, which is related to energy. Slide 22 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC The THREE parts are:a) (Near) UVA - tanning, wrinkles (is the light closest to optical or visible light) b) (Far) UVB - sunburn, cancer (lies between the UVA and UVC ultraviolet regions) c) (Extreme) UVC - most harmful, sterilization (the ultraviolet light closest to X-rays, and is the most energetic of the three types) Slide 23 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1.6 X rays An x-ray photon contains considerably more energy than a visible light photon or an RW photon. The frequency of x-radiation is much higher and the wavelength much shorter than for other types of EM radiation. X-rays are emitted from the electron cloud of an atom that has been stimulated artificially. X-rays are produced in diagnostic imaging systems. Slide 24 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen, a German scientist who found them quite by accident when experimenting with vacuum tubes. Slide 25 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.1.7 Gamma rays Gamma-rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells. Slide 26 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.2 Electromagnetic Spectrum TOPIC 2.2.2 Relevant in Medical Imaging Three regions of the electromagnetic spectrum are particularly important in medical imaging. Naturally, x-ray region is fundamental to produce a high-quality radiograph. The visible light region is also important because the viewing conditions of a radiographic or fluoroscopic image are critical to diagnosis. With the introduction of magnetic resonance imaging (MRI), the radiofrequency region has become more important in medical imaging. Slide 27 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.3 Wave Particle Duality TOPIC The idea of duality originated in a debate over the nature of light and matter that dates back to the 17th century. Wave particle duality postulates that all particles exhibit both wave and particle properties with regards to:- A) Wave Theory B) Particle Theory Slide 28 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.3 Wave Particle Duality TOPIC 2.3.1 Wave Theory Electromagnetic radiation is a form of energy with the properties of a wave. A wave is a disturbance that propagates from one place to another. The easiest type of wave to visualize is a transverse wave, where the displacement of the medium is perpendicular to the direction of motion of the wave. In a longitudinal wave, the displacement is along the direction of wave motion. Slide 29 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.3 Wave Particle Duality TOPIC Slide 30 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.3 Wave Particle Duality TOPIC One thing that all the forms of electromagnetic radiation have in common is that they can travel through empty space. This is not true of other kinds of waves; sound waves, for example, need some kind of material, like air or water, in which to move. Sound waves are longitudinal waves. Slide 31 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.3 Wave Particle Duality TOPIC 2.3.2 Quantum (Particle) Theory Energy of an electromagnetic wave is quantized. Electromagnetic energy is emitted and absorbed as discrete packets of energy or quanta called photons. The energy of the photons is proportional to the frequency of the wave: E is the energy, h is Planck's constant, and f is frequency The energy is commonly expressed in the unit of electron volt (eV). The photons with the highest energy correspond to the shortest wavelengths. Slide 32 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.4 Propagation of Electromagnetic Radiation TOPIC 2.4.1 Through Material The propagation involves the absorption and reemission of the wave energy by the atoms of the material. When it impinges upon the atoms of a material, the energy of that wave is absorbed and causes the electrons within the atoms to undergo vibrations. The vibrating electrons create a new electromagnetic wave with the same frequency as the first. Then, the energy is reemitted by an atom, it travels through a small region of space between atoms. Once it reaches the next atom, the process will reoccur. Slide 33 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.4 Propagation of Electromagnetic Radiation TOPIC 2.4.2 Through Vacuum When it travels at a speed of c (3 x 108 m/s) through the vacuum of interatomic space, the absorption and reemission process causes the net speed of the electromagnetic wave to be less than c. Slide 34 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.4 Propagation of Electromagnetic Radiation TOPIC Slide 35 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.5 Inverse Square Law TOPIC When a light is emitted from a source such as the sun or light bulb, the intensity decreases rapidly with the distance from the source. X-rays exhibit precisely the same property. This decrease in intensity is inversely proportional to the square of the distance of the object from the source. Mathematically, this is called the inverse square law and is expressed as follows: Slide 36 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.5 Inverse Square Law TOPIC The inverse square law describes the relationship between radiation intensity and distance from the radiation source. Slide 37 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.5 Inverse Square Law TOPIC The reason for the rapid decrease in intensity with increasing distance is that the total light emitted is spread out over an increasingly larger area. For example: The reduction of wave amplitude with distance from the source. To apply the inverse square law, you must know three of the four parameters, which consist of two distances and two intensities. This relationship between EM energy (radiation) intensity and distance from the source applies equally well to x-ray intensity. Slide 38 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.5 Inverse Square Law TOPIC Slide 39 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION 2.6 References TOPIC No. REFERENCES 1 Ball, J., Moore, A. D., & Turner, S. (2008). Essential physics for radiographers. Blackwell. 2 Bushong, S. C. (2008). Radiologic science for technologists. Canada: Elsevier. Slide 40 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION SUMMARY TOPIC Electromagnetic radiation are transverse waves, similar to water waves in the ocean or the waves seen on a guitar string. A photon is the smaller quantity of any type of EM energy. EMR Sine Waves have amplitude, wavelength, velocity and frequency which cause the waves to affect matter differently Electromagnetic spectrum includes the entire range of electromagnetic radiation. Wave particle duality postulates that all particles exhibit both wave and particle properties. Slide 41 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION NEXT SESSION PREVIEW TOPIC CHAPTER 3: X-RAY PRODUCTION Slide 42 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION Activity TOPIC Define or otherwise identify the following: a) Electromagnetic Radiation Answer b) Frequency Answer c) Amplitude Answer d) Velocity Answer e) Wavelength Answer Slide 43 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION Activity TOPIC Explain the Wave-Particle Duality with its theories. Answer List the types of electromagnetic radiation. Answer Describe the difference between photons and particles. Answer Slide 44 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION Activity TOPIC The speed of sound in air is approximately 340 m/s. the highest treble tone that a person can hear is about 20kHz. What is the wavelength of this sound? (v = f) Answer The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR (4 mGya) at 90 cm. What will the exposure be at 180 cm? Answer Slide 45 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION APPENDIX TOPIC FIGURE SOURCE Figure 1 http://www.universetoday.com/wp-content/uploads/2009/12/Democritus.jpg Figure 2 Figure 3 http://3.bp.blogspot.com/_nW9kILlRDjU/THYkY9gTwnI/AAAAAAAAAAM/YFmQh 2QLfw4/s1600/John+Dalton.jpg Figure 4 http://abyss.uoregon.edu/~js/images/atom_prop.gif Figure 5 http://upload.wikimedia.org/wikipedia/commons/c/c1/J.J_Thomson.jpg Figure 6 http://2011period6group4.wikispaces.com/file/view/Thomson's_Model.gif/1684 83477/Thomson's_Model.gif Figure 7 http://www.vias.org/physics/img/rutherford.jpg Figure 8 http://i54.tinypic.com/n2l3r9.png Figure 9 http://abyss.uoregon.edu/~js/images/nbohr.gif Figure 10 http://cdn.timerime.com/cdn-33/users/13890/media/Atom_diagram.jpg Slide 46 of 38 CHAPTER 2: ELECTROMAGNETIC RADIATION APPENDIX TOPIC FIGURE SOURCE Figure 11 Figure 12 http://1.bp.blogspot.com/_SmG3fxIEtUk/TD7yf3eF7XI/AAAAAAAADKQ/uziSUELf Bwc/s1600/proton.jpg Figure 13 http://www.cartage.org.lb/en/themes/sciences/chemistry/generalchemistry/a tomic/BasicStructure/atmparts.gif Figure 14 http://www.chemistryland.com/ElementarySchool/BuildingBlocks/NeutronProt onElectronLight.jpg Figure 15 Figure 16 http://www.medcyclopaedia.com/upload/book%20of%20radiology/chapter03/ni c_k3_0.jpg Figure 17 http://www.boluodusmyportfolio.com/Images/radioactivity2.gif Figure 18 http://www.universetoday.com/wp-content/uploads/2011/04/RadioactiveIsotopes.jpg Slide 47 of 38
