Types of Radiation Lecture PDF

Types of radiation Dr. Nahla Atallah  Contents Photons Relationship between velocity, frequency and wavelength Ultrasound waves & Electromagnetic waves Visible Light Infrared & Ultraviolet Light Radiofrequency waves Microwave Ionizing radiati...

Types of radiation Dr. Nahla Atallah  Contents Photons Relationship between velocity, frequency and wavelength Ultrasound waves & Electromagnetic waves Visible Light Infrared & Ultraviolet Light Radiofrequency waves Microwave Ionizing radiation Waves And Particles X-Rays & Gamma Rays Inverse Square Law  PHOTONS WERE first described by the ancient Greeks  Today, photons are known as electromagnetic energy;  Electromagnetic energy is present everywhere and exists over a wide energy range. X-rays, visible light, and radiofrequencies are examples of electromagnetic energy.  Ever present all around us is a state of energy called electromagnetic energy.  A photon is the smallest quantity of any type of electromagnetic energy, just as an atom is the smallest quantity of an element.  A photon may be pictured as a small bundle of energy, sometimes called a quantum, that travels through space at the speed of light.  We speak of x-ray photons, light photons, and other types of electromagnetic energy as photon radiation.  Photons are energy disturbances that move through space at the speed of light (c). The sine waves in Figure 3-1 are identical except or their amplitude; Sine wave A has the largest amplitude, and sine wave C has the smallest. Review of Radiation Oncology Physics: A Handbook for Teachers and Students - 1. Sine waves exist in nature and are associated with many familiar objects (Figure 3-2). Simplistically, sine waves are variations of amplitude over time. Review of Radiation Oncology Physics: A Handbook for Teachers and Students - 1.  Frequency and Wavelength **The wavelength is the distance from one crest to another  Relationship between velocity, frequency and wavelength  Three wave parameters—velocity, frequency, and wavelength—are needed to describe electromagnetic energy.  *A change in one affects the value of the others.  *Velocity is constant. Ultrasound waves & Electromagnetic waves  Measurement of the Electromagnetic Spectrum  The electromagnetic spectrum shown in Figure 3-6 contains three different scales, one each for energy, frequency, and wavelength.  Because the velocity of all electromagnetic energy is constant, the wavelength and frequency are inversely related.  Visible Light  An optical physicist describes visible light in terms of wavelength. When sunlight passes through a prism (Figure 3-7), it emerges not as white sunlight but as the colors for the rainbow  Although photons of visible light travel in straight lines, their course can be deviated when they pass from one transparent medium to another.  This deviation in line of travel, called refraction.  Visible light occupies the smallest segment of the electromagnetic spectrum, and yet it is the only portion that we can sense directly.  Sunlight also contains two types of invisible light: infrared and ultraviolet.  Infrared & Ultraviolet Light  Infrared light consists of photons with wavelengths longer than those of visible light but shorter than those of microwaves.  Infrared light heats any substance on which it shines. It may be considered radiant heat.  Ultraviolet light is located in the electromagnetic spectrum between visible light and ionizing radiation.  It is responsible for molecular interactions that can result in sunburn.  Radiofrequency waves  A radio or television engineer describes radio waves in terms of their frequency. For example, radio station WIMP might broadcast at 960 kHz, and its associated television station WIMP-TV might broadcast at 63.7 MHz Communication broadcasts are usually identified by their frequency of transmission and are called radiofrequency (RF) emissions.  Radiofrequency covers a considerable portion of the electromagnetic spectrum.  RF has relatively low energy and relatively long wavelength.  Microwave  Microwave frequencies vary according to use but are always higher than broadcast RF and lower than infrared.  Microwaves have many uses, such as cellular telephone communication, highway speed monitoring, medical diathermy, and hotdog preparation.  Ionizing Radiation  An x-ray photon contains considerably more energy than a visible light photon or an RF photon.  The frequency of x-radiation is much higher and the wavelength much shorter than or other types of electromagnetic energy.  WAVES AND PARTICLES  A photon of x-radiation and a photon of visible light are fundamentally the same except that x-radiation has much higher frequency, and hence a shorter wavelength, than visible light.  These differences result in differences in the way these photons interact with matter.  Visible-light photons tend to behave more like waves than particles.  The opposite is true of x-ray photons, which behave more like particles than waves.  In fact both types of photons exhibit both types of behaviour—a phenomenon known as the wave-particle duality of electromagnetic energy. X-Rays & Gamma Rays Review of Radiation Oncology Physics: A Handbook for Teachers and Students - 1. There are three degrees of interaction between light and an absorbing material: transparency, translucency, and opacity (Figure 3-13).  Inverse Square Law  When light is emitted from a source such as the sun or a light bulb, the intensity decreases rapidly with the distance from the source. This decrease in intensity is inversely proportional to the square o the distance of the object from the source.  Mathematically, this is called the inverse square law and is expressed as follows:  References  Radiologic Science for Technologists: Physics, Biology, and Protection, 11th edition.