Radiation Types, Sources, and Doses Received Ch. 2 PDF

Chapter 2 Radiation: Types, Sources, and Doses Received  Radiation Types, Sources, and Doses Received  Radiation has different types and sources.  Some types of radiation produce damage in biologic tissue, whereas others do not.  Sources  Natura...

Chapter 2 Radiation: Types, Sources, and Doses Received  Radiation Types, Sources, and Doses Received  Radiation has different types and sources.  Some types of radiation produce damage in biologic tissue, whereas others do not.  Sources  Natural that are always present in the environment.  Human-made created by humans for specific purposes.  Both sources contribute a percentage of the total amount of radiation that humans receive during their lifetime.  Radiation  Energy  The ability to do work—that is, to move an object against resistance.  How radiation relates to energy  Radiation refers to energy that passes from one location to another and can have many manifestations. This means that many types of radiation exist.  Types of Radiation  Box 2.1  Mechanical vibration of materials  Ultrasound  The electromagnetic wave  Radio waves  Microwaves  Infrared  Visible light Ultraviolet  X-rays  Gamma rays  The Electromagnetic Spectrum  Electromagnetic spectrum  The full range of frequencies and wavelengths of electromagnetic waves (see Table 2.1 in textbook)  For calculation of the wavelength and energy of electromagnetic radiation (see Box 2.2 in the textbook).  Electromagnetic Waves  In electromagnetic waves, electric and magnetic fields fluctuate rapidly as they travel through space.  Electromagnetic waves are characterized by their:  Frequency  Wavelength  Dual nature of electromagnetic radiation (wave- particle duality)  This form of radiation can travel through space in the form of a wave but can interact with matter as a particle of energy. Ionizing and Nonionizing Radiation  To study radiation protection, the electromagnetic spectrum can be divided into two parts.  Ionizing radiation (x-rays, gamma rays, and high-energy ultraviolet radiation [energy higher than 10 eV]) can transfer sufficient energy to some orbital electrons to remove them from the atoms to which they were attached (the process of ionization, the foundation of the interaction of x-rays with human tissue).  Nonionizing radiation (ultraviolet radiation [energy less than 10 eV], visible light, infrared rays, microwaves, and radio waves) does not have sufficient kinetic energy to eject electrons from atoms.  Ionizing Radiation  Ionization  Conversion of atoms to ions  Makes tissues valuable for creating images  Has the undesirable result of potentially producing some damage in the biologic material  The amount of energy transferred to electrons by ionizing radiation is the basis of the concept of radiation dose.  Particulate Radiation  Form of radiation that includes alpha particles, beta particles, neutrons, and protons.  All these are subatomic particles that are ejected from atoms at very high speeds.  They possess sufficient kinetic energy to be capable of causing ionization by direct atomic collision.  No ionization occurs when the subatomic particles are at rest.  Alpha Particles (1 of 3)  Alpha rays  Emitted from nuclei of very heavy elements such as uranium and plutonium during the process of radioactive decay  Each contains two protons and two neutrons.  Are simply helium nuclei (i.e., helium atoms minus their electrons)  Have a large mass (approximately four times the mass of a hydrogen atom) and a positive charge twice that of an electron  Alpha Particles (2 of 3)  Particulate radiations vary in their ability to penetrate matter.  Alpha particles are less penetrating than beta particles (fast electrons).  They lose energy quickly as they travel a short distance in biologic matter  Considered virtually harmless.  Alpha Particles (3 of 3)  As an internal source of radiation, they can be very damaging.  If emitted from a radioisotope deposited in the body, such as in the lungs, alpha particles can be absorbed in the relatively radiosensitive epithelial tissue and are very damaging to that tissue.  Beta Particles (1 of 2)  Beta rays  Identical to high-speed electrons except for their origin  8000 times lighter than alpha particles and have only one unit of electric charge (−1) as compared with the alpha’s two units of electric charge (+2).  Will not interact as strongly with their surroundings as alpha particles do.  Capable of penetrating biologic matter to a greater depth than alpha particles with less ionization along their paths.  Beta Particles (2 of 2)  Produced in a radiation oncology treatment machine called a linear accelerator  Use  To treat superficial skin lesions in small areas  To deliver radiation boost treatments to breast tumors at tissue depths typically not exceeding 7 to 8 cm  Require either millimeters of lead or multicentimeter thick slabs of wood to absorb them  For energies of less than 2 meV, either a 1-cm thick block of wood or a 1-mm thick lead shield would be sufficient for absorption.  Protons  Positively charged components of an atom  Have a relatively small mass that, however, exceeds the mass of an electron by a factor of 1800  Number of protons in the nucleus of an atom constitutes its atomic number, or Z number (see Appendix D in textbook)  Neutrons  Electrically neutral components of an atom  Have approximately the same mass as a proton  If two atoms have the same number of protons but a different number of neutrons in their nuclei, they are referred to as isotopes.  If one of these combinations of Z protons and some neutrons leads to an unstable nucleus, then that combination is called a radioisotope.  Introduction to the Concept of Radiation Dose  Absorbed dose: the amount of kinetic energy per unit mass that has been absorbed in a material due to its interaction with ionizing radiation.  Measured in units of milligray (mGy).  Equivalent Dose (EqD)  Takes into account the type of ionizing radiation that was absorbed.  Provides an overall dose value that includes the different degrees of tissue interactions that could be caused by different types of ionizing radiation.  Measured in units of the millisievert (mSv)  Effective Dose (EfD)  Takes into account the dose for all types of ionizing radiation (e.g., alpha, beta, gamma, x-ray) to various irradiated organs or tissues in the human body (e.g., skin, gonadal tissue, thyroid)  Intended to be the best estimate of overall harm that might be produced by a given absorbed dose of radiation in human tissue.  Measured in units of the millisievert (mSv)  Biologic Damage Potential  Ionizing radiation primarily causes biologic damage.  Produced by ionizing radiation while penetrating body tissues primarily by ejecting electrons from atoms composing the tissues  Result of destructive radiation interaction at the atomic level  Molecular change  Cellular damage  Organic damage (see Table 2.2 in textbook)  Sources of Radiation (1 of 3)  Natural radiation  Human-made (artificial) radiation  Fig 2.2 demonstrates the contribution of various sources to the average annual effective dose per person in the U.S. in 2016.  Dose from natural background radiation is approximately 3.1 mSv annually  Annual dose from medical radiation is approximately 2.3 mSv  Annual dose from human-made radiation is approximately 0.1 mSv annually  Annual dose from natural background radiation is approximately 3.1 mSv  Annual dose from all-natural, medical and human-made radiation is approximately 5.5 mSv  Sources of Radiation (2 of 3)  Natural radiation (natural background radiation)  Terrestrial radiation (e.g., radon, thoron)  Cosmic radiation (solar and galactic)  Internal radiation from radioactive atoms (also called radionuclides)  See Table 2.3 in textbook for average annual radiation equivalent dose per person  Sources of Radiation (3 of 3)  Human-made (artificial) radiation  Consumer products containing radioactive material  Air travel  Nuclear fuel for generation of power  Atmospheric fallout from nuclear weapons testing  Nuclear power plant accidents (TMI-2 and Chernobyl)  Nuclear power plant accidents as a consequence of natural disasters (Fukushima)  Medical Radiation (1 of 3)  Medical radiation exposure results from the use of diagnostic x-ray machines and radiopharmaceuticals in medicine.  The two largest sources of artificial radiation are  Radiography and Fluoroscopy  Computed Tomography (CT) procedures  Accounts for approximately 2.3 mSv of the average annual individual EfD.  Exposure to human-made radiation in medical applications continues to increase rapidly  Medical Radiation (2 of 3)  Because of the large variety of radiologic equipment and differences in imaging procedures and in individual radiologist and radiographer technical skills, patient dose for each examination varies according to the facility providing imaging services.  Medical Radiation (3 of 3)  The amount of radiation received by a patient from diagnostic x-ray procedures may be indicated in terms of the following  Entrance skin exposure (ESE), which includes skin and glandular dose  Bone marrow dose  Gonadal dose  The End  Chapter Summary  General Discussion Questions  Review Questions