Electromagnetic Radiation PDF

Physical Principles of Electromagnetic Radiation Physics for Biomedical Sciences Dr Irene Polycarpou Outline Radiation Sources of Radiation Cosmic Radiation Electromagnetic Radiation Ionizing Radiation Electromagnetic Theory Application of Electromagnetic Radiation Radio Waves Microwaves...

Physical Principles of Electromagnetic Radiation Physics for Biomedical Sciences Dr Irene Polycarpou Outline Radiation Sources of Radiation Cosmic Radiation Electromagnetic Radiation Ionizing Radiation Electromagnetic Theory Application of Electromagnetic Radiation Radio Waves Microwaves Infrared Waves Visible Light Ultraviolet Waves X-Rays Gamma Rays A block of graphite is made up of carbon atoms. Each carbon atom has a dense central nucleus made up of protons and neutrons. Protons and neutrons are made up of different combinations of quarks. ✓ The outer boundary of the city is the limit of the atom. ✓ The central city square is the nucleus. ✓ The buildings in the city square are the protons and neutrons. ✓ The bricks the buildings are made out of are the quarks. What is radiation? You know more about it than you think. Radiation is simply the release of energy. The most familiar form of radiation in our life is visible light, like that produced by the sun, or a light bulb. In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. Where does radiation come from? Radiation occurs when energy is emitted by a source, then travels through a medium, such as air, until it is absorbed by matter. Radiation: Energy as a wave or particle In addition to waves, atoms are known to radiate particles. These are all tiny (measured in 100-trillionths of an inch) and known to us only indirectly through their effects. Some of the more important particles are: Electrons The lightest particles, carrying a negative electric charge. Radiation electrons are sometimes called beta rays. Protons About 2,000 times as heavy as electrons and positively charged. Neutrons Like protons, but uncharged. Alpha Particles Each one is assembled of two protons and two neutrons. Cosmic Radiation The earth’s atmosphere is bombarded by high-energy particles from our galaxy (primary cosmic radiation). In the upper atmospheric layers, these particles react with air molecules. As a result of nuclear reactions, a great number of secondary particles (secondary cosmic radiation), is formed.  9 Cosmic Radiation  10 Cosmic Radiation Cosmic rays are extremely high-energy subatomic particles – mostly protons and atomic nuclei accompanied by electromagnetic emissions – that move through space, eventually bombarding the Earth’s surface. We recognize two different types: 1. Galactic Remnants of supernovas, which are powerful explosions during the last stages of massive stars that either collapse to black holes or are destroyed. Energy release in the explosion, accelerates charged particles outside our solar system. 2. Solar Charged particles emitted by the Sun, predominantly electrons, protons and helium nuclei. Electromagnetic Wave Electromagnetic radiation – form of energy that is created through the interactions of electric and magnetic fields. Displays wave-like behavious as it travels through space. What’s the connection between light, microwaves and X-rays? They are all different types of electromagnetic radiation that travel as waves and transfer energy from one place to another. Different electromagnetic waves carry different amount of energy Electromagnetic spectrum The entire distribution of electromagnetic radiation according to frequency or wavelength. Electromagnetic spectrum Types of Radiation Non-ionizing radiation has enough energy to excite atoms, making them move more rapidly. Microwaves work by RAPID exciting water molecules, creating MOVEMENT friction. The friction creates heat, and the heat warms the food. Radio transmissions, cell phones, visible light. Ionizing radiation has enough energy to remove electrons from their orbits, creating ions. High-level ultraviolet light, X-rays, gamma rays. Types of Radiation Types of Radiation Ionization If radiation transfers energy to an orbiting electron which is equal to or greater than the electron’s binding energy, then the electron is ejected from the atom. The positive charged atom and the ejected electron are called an ion pair. Ionizing radiation: energy greater than 13.6 eV. Medical imaging: ionizing radiation with energies of 24 keV – 500 keV Ionization vs. excitation Ionization: electron is ejected from the atom Occurs when transferred energy exceeds the binding energy. Electron is ejected from the atom. Results in an ion pair consisting of an ejected electron and a positively charged atom. Excitation: electron moves to a higher orbit Occurs when energy transferred to an electron does not exceed its binding energy Following excitation, de-excitation occurs as the electron returns to a lower energy level releasing energy by either: a. Emitting it in the form of electromagnetic radiation or b. Transferring the energy to a weakly bound orbital electron Excitation Excitation occurs when energy transferred to an electron does not exceed its binding energy. Following excitation, de- excitation occurs as the electron returns to a lower energy level releasing energy. De-excitation Electrons do not stay in excited states for very long - they soon return to their ground states, emitting a photon with the same energy as the one that was absorbed. Types of ionizing radiation Types of ionizing radiation Types of ionizing radiation Alpha radiation ✓ Happens when the unstable atom emits two protons and two neutrons—basically a helium nucleus. ✓ The original atom, with fewer protons and neutrons, becomes a different element. Types of ionizing radiation Beta radiation ✓ An atom decays by giving off a high-energy, high-speed particle that has a negative or positive charge. ✓ Particles smaller and more energetic than alpha particles. ✓ Beta minus decay and beta plus decay (positron emission) Types of ionizing radiation Gamma radiation and x-ray ✓ High energy waves that can travel great distances at the speed of light. ✓ X-rays stopped by dense materials (bone, tumors or lead) ✓ Gamma rays can penetrate further with higher energy (target and eliminate tumors, several inches of lead) Ionization density Measures the number of ionization events, such as electron or photon interactions, per unit volume in a substance. Critical parameter for understanding the biological effects of ionizing radiation and assessing radiation damage in materials and living tissues. Penetration ability Ability of radioactive emission to go through matter. Penetration ability Epidermis Dermis Hypodermis Penetration ability Alpha particles: Cannot penetrate most matter. Dead outer layers of skin is sufficient to stop alpha particles. Beta particles: Capable of penetrating the skin and causing radiation damage, such as skin burns. They can be stopped by a layer or two of clothing or by a few millimeters of a substance such as aluminum. Gamma rays: Very penetrating. Several feet of concrete or a few inches of lead required to stop gamma rays. X-rays: Lower in energy than gamma. Most diagnostic medical x-rays are stopped by a few millimeters of lead. Radiation and radioactivity Radiation: Energy in transit, either particulate or electromagnetic in nature Radioactivity: The characteristic of various materials to emit ionizing radiation Ionization: The removal of electrons from an atom. The essential characteristic of high-energy radiation when interacting with matter.  33 Electromagnetic spectrum Forms of radiation include radio waves, microwaves, ultraviolet light, and X-rays and Gamma rays used in medical procedures Electromagnetic Theory How are electromagnetic waves produced? Electricity and magnetism were once thought to be separate forces. However, in 1873, Scottish physicist James Clerk Maxwell developed a unified theory of electromagnetism. The study of electromagnetism deals with how electrically charged particles interact with each other and with magnetic fields. James Clerk Maxwell (13 Jun 1831 - 5 Nov 1879) Scottish mathematician and physicist whose researches united electricity and magnetism into the concept of the electro-magnetic field. Electromagnetic Theory There are four main electromagnetic interactions: The force of attraction or repulsion between electric charges is inversely proportional to the square of the distance between them. Magnetic poles come in pairs that attract and repel each other, much as electric charges do. An electric current in a wire produces a magnetic field whose direction depends on the direction of the current. A moving electric field produces a magnetic field, and vice versa. Electromagnetic Waves Electromagnetic waves are transverse waves made up of electric and magnetic fields. Can be produced by vibrating an electric charge. It has an electric and magnetic field associated Motion with it. Magnetic Electric Field Field  37 What is light made of? Light is made of particles called photons, bundles of the electromagnetic field that carry a specific amount of energy. Mechanical vs. electromagnetic waves Needs a medium to Does not need a medium to propagate. propagate. i. X-rays i. Water ii. Radio waves ii. Sound iii. Light 39 Mechanical waves Mechanical waves can be: 1. Transverse waves 2. Longitudinal waves 3. Surface Waves Longitudinal waves  45 crest Wavelength () Amplitude trough Period (T): time for one wave to pass a point Frequency (f): # of waves passing a point per second  46 Comparison of transverse waves  Long wavelength, low frequency  Short wavelength, high frequency Short wavelength  short period, high frequency Long wavelength  long period, low frequency Properties of electromagnetic radiation 1. Electromagnetic radiation can travel through empty space. Most other types of waves must travel through some sort of substance. 2. All electromagnetic waves travel at the same speed. The speed of light is always a constant. (In a vacuum the speed of light : 2.99792458 x 108 m s-1) 3. Wavelengths are measured between the distances of either crests or troughs. It is usually characterized by the Greek symbol λ. Note: When light travels through matter, its speed is less than the speed of light in vacuum and is given by the refraction equation: cn=c/n , where n is the the index of refraction of the matter. Example 1 a. What is the wavelength of cell phone radiation? Frequency = 850 MHz b. What is the wavelength of a microwave oven? Speed of light Frequency = 2.45 GHz c= 2.99792458 x 108 m s-1 Light as a particle Light acts as if it consists of particles called photons, with discrete energy. Each particle of light or photon has energy. The energy is related with its frequency: E = h f = (h c )/λ (sometimes frequency is denoted as v) Max Planck Nobel prize in Physics in 1918 The shorter the wavelength (and higher the frequency) of electromagnetic waves, the more energy that they carry. Increase of energy results in increase in hazard. Light as a particle Light as a particle & a wave Example 2 a. What is the frequency of UV light with a wavelength of 230 nm? b. What is the energy of 1 photon of UV light with wavelength = 230 nm? Remember the formula E=h x f =h x c/λ Photon Particle that comprises waves of electromagnetic radiation. 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. 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. How do electromagnetic waves travel? Electromagnetic waves can travel through a vacuum, as well as through matter. The transfer of energy by electromagnetic waves traveling through matter or across space is called electromagnetic radiation. What happens when they hit a surface? When electromagnetic waves hit a surface, they can be reflected, absorbed or transmitted. How the waves behave, depends on their energy and the type of material. For example, light waves are reflected by skin but X-rays pass straight through. If electromagnetic waves are absorbed, some of their energy is absorbed by the material. This usually increases the temperature of the material Application of the Electromagnetic Spectrum in Medicine Radio waves Have the longest wavelengths and the lowest frequencies; wavelengths range from 1000s of meters to.001 m Used in: RADAR, cooking food, satellite transmissions Radio waves In 1887, Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Their frequencies range from 3kHz to 300GHz. Radiofrequency is a rate of oscillation in the range of radio waves, it refers to electrical rather than mechanical oscillations. Radio waves are used in medicine e.g. MRI and RFA. Heinrich Hertz Radio waves MRI and RF (Radio Frequency) Used to produce images of soft tissues, fluid, fat and bone. Does this by producing a map which depends on the density of hydrogen in the body. Uses strong superconducting magnet with a magnetic field strength 40,000 x that of the Earth’s. It is used to diagnose many problems e.g. helps identify tumors. Radio waves Radiofrequency Ablation Radiofrequency Ablation (RFA) uses heat to destroy cancer cells. It uses a probe (electrode) to apply an electric current to a tumor. The electric current heats the cancer cells to high temperatures, which ablates the cells. The cancer cell dies and the area that’s being treated gradually shrinks and becomes scar tissue. It doesn’t always work in one go. Radio waves Radiofrequency Ablation Radio waves Radiofrequency Ablation Microwaves Type of electromagnetic wave with wavelengths in the millimeter to meter range, residing between radio waves and infrared radiation. Microwaves heat food and liquids by resonating water molecules, a principle utilized in microwave ovens for cooking and reheating. Range from 300GHz to 300MHz  66 Microwaves Hyperthermia Hyperthermia therapy is a type of medical treatment in which body tissue is exposed to slightly higher temperatures to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation and certain anti-cancer drugs.  67 Infrared waves Infrared waves (heat): Have a shorter wavelength, from.001 m to 700 nm, and therefore, a higher frequency (300 GHz to 400 THz) Used for finding people in the dark and in TV remote control devices  68 Infrared waves Pulse oximetry The pulse oximeter uses two lights to analyze hemoglobin. 1. Red light, which has a wavelength of approximately 650 nm. 2. Infrared light, which has a wavelength of 950 nm. Infrared waves Pulse oximetry Infrared waves Infrared vision Infrared vision is the capability to perceive and interpret infrared radiation, allowing for the detection of heat patterns and objects not visible in the visible light spectrum. Infrared waves Infrared vision for locating tumors Thermographic Imaging: Infrared vision, or thermographic imaging, is used to locate tumors by detecting abnormal heat patterns in the body. Increased Metabolic Activity: Tumors often exhibit increased metabolic activity, generating heat that is detectable in the infrared spectrum. ✓ Early Detection: Infrared vision can aid in the early detection of tumors by identifying regions with elevated temperatures, allowing for timely medical intervention. Infrared waves Thermographic imaging (thermography) Non-Invasive Imaging: Thermography in medicine is a non-invasive diagnostic technique that uses infrared cameras to detect and visualize variations in skin temperature. Early Warning: It can provide early warning signs of various medical conditions, including breast cancer and vascular disorders, by identifying abnormal heat patterns or temperature irregularities in the body. Infrared waves Thermographic imaging (thermography) NORMAL Good thermal symmetry with no suspicious thermal findings. These patterns represent a baseline that won’t alter over time and can only be changed by pathology. FIBROCYSTIC Significant vascular activity in the left breast. This was clinically coorelated with fibrocystic changes. Visible light Visible light: Wavelengths range from 750 nm (red light) to 380 nm (violet light) with frequencies from 400 THz to 700 THz. These are the waves in the EM spectrum that humans can see. Visible light waves are a very small part of the EM spectrum! Visible light Red Orange Yellow Blue Green Violet Visible light Can be detected by the human eye. Wavelengths range approximately from 700- 400nm. In the 17th Century, Isaac Newton explained the optical spectrum in his book ‘Opticks’. He divided the spectrum into seven named colours: ROYGBIV. The actual concept of a visible ‘spectrum’ was defined in the early 19th century when light outside the visible range was discovered e.g. Sir Isaac Newton Johann Ritter with Ultraviolet Light. Infrared waves Endoscopy Allows us to look inside the human body through a narrow, flexible scope.  It is mostly used to diagnose problems in the oesophagus, stomach and intestines, including ulcers, bleeding and tumours.  Typically optical fibres are used to transfer light to the end of the endoscope and a miniature video camera records the image, and viewed on a video screen. Ultraviolet waves Wavelengths range from 400 nm to 10 nm; the frequency between 800 THz to 30 PHz (and therefore the energy) is high enough with UV rays to penetrate living cells and cause them damage. Ultraviolet waves Sunlight is the main source of UV. Although we cannot see UV light, bees, bats, butterflies, some small rodents and birds can. UV on our skin produces vitamin D in our bodies. Too much UV can lead to sunburn and skin cancer. UV rays are easily blocked by clothing. Used for sterilization because they kill bacteria. UVA (315-400 nm) UVB (280-315 nm) Sun over UV filter. UVC (100-280 nm) Ultraviolet waves Ultraviolet waves Medicine Vitiligo Used for treatment of skin disorders such as: Psoriasis, Eczema, Vitiligo Psoriasis Ultraviolet waves Dentistry Ultraviolet light produces free radicals that activate the catalyst and speed up polymerisation of the composite resin. Ultraviolet light hardening a patient’s filling Ultraviolet waves Sterilisation Used for sterilization because it kills bacteria. Ultraviolet light’s effect on cell data.  86 X-rays Wavelengths from 10 nm to.001 nm. These rays have enough energy to penetrate deep into tissues and cause damage to cells; are stopped by dense materials, such as bone. Frequencies of 30 PHz to 30EHz  87 X-rays  They were discovered serendipitously by German Physicist Wilhelm Roentgen in 1895.  Roentgen was working with electron beams in discharge tubes.  In the early days many patients and doctors developed radiation sickness since they were shining x-rays in all directions for large amounts of time. Wilhelm Roentgen X-rays X-ray machine Used to look at solid structures, such as bones and bridges (for cracks), and for treatment of cancer. X ray machine The heart of the x-ray machine is the electrode pair. A Cathode (heated filament) and the Anode (made of Tungsten) The Cathode source accelerates electrons to a high speed and these electrons then collide with the Tungsten. X-rays Computerized tomography (CT) A computerized tomography (CT) scan is usually a series of X-rays taken from different angles and then assembled into a three-dimensional model. Gamma rays Carry the most energy and have the shortest wavelengths, less than one trillionth of a meter and frequency above 30 EHz. Gamma rays have enough energy to go through most materials easily; you would need a 3-4 ft thick concrete wall to stop them! Gamma rays EM Radiation high frequency High energy photon- kill cancer cells Produced by decay from high energy states of atomic nuclei Discovered in 1900 by Paul Villard. Paul Villard Gamma rays Gamma rays are released by nuclear reactions in nuclear power plants, by nuclear bombs, and by naturally occurring elements on Earth. Sometimes used in the treatment of cancers. Gamma rays Stintigraphy A diagnostic test in Nuclear Medicine that creates images of the body's internal organs and tissues using gamma rays emitted by radioactive isotopes. Example: The patient was given a slightly radioactive gas to breath, and the picture was taken using a gamma camera to detect the radiation. The colors show the air flow in the lungs. Gamma rays Positron Emission Tomography (PET) Involves the detection of gamma rays resulting from the annihilation of positrons (antiparticles of electrons) within the body's tissues. PET uses radiolabeled tracer molecules that emit positrons, and when these collide with electrons in the body, they annihilate, producing gamma rays that are detected by the PET scanner. Gamma rays Positron Emission Tomography (PET) Images from PET scans are interpreted by mapping the distribution of radiolabeled tracers, as areas with higher tracer uptake indicate regions of increased metabolic activity, often associated with diseases or abnormalities. Thank you!