Chapter 1 Radiation PDF

## Chapter 1 Radiation ### Objectives At the end of this chapter the student will be able to: - Define the definition of radiation - Identify the types of radiation - Recognize the sources of radiation - Satisfy information about the factor determined the effect of radiation - Recognize the methods...

## Chapter 1 Radiation ### Objectives At the end of this chapter the student will be able to: - Define the definition of radiation - Identify the types of radiation - Recognize the sources of radiation - Satisfy information about the factor determined the effect of radiation - Recognize the methods to identify the radiation dose ### Definition of radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: - **Electromagnetic radiation**, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ) - **Particle radiation**, such as alpha radiation (α), beta radiation (β), and neutron radiation (particles of non-zero rest energy) - **Acoustic radiation**, such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium) - **Gravitational radiation**, radiation that takes the form of gravitational waves, or ripples in the curvature of space-time Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere. ### Types of radiation - **Non-ionizing radiation:** Any type of electromagnetic radiation that does not carry enough energy to ionize an atom is called non-ionizing radiation. An atom becomes ionized when it loses or gains an electron. Ionizing radiation causes a chemical change and thus causes more damage than non-ionizing radiation. Still, observable effects can be tracked from non-ionizing radiation. - **Ionizing radiation:** The nucleus of an atom can decay or transform releasing energy in the form of either particles or waves. Examples of **non-ionizing radiation** include: - Visible light - Infrared light - Microwaves - Radio waves The light from the sun that reaches Earth is largely non-ionizing radiation, yet some ultraviolet rays (which have the ability to ionize) do reach the surface of Earth as well. Infrared or laser light can cause burns to skin and damage to eyes, depending on the levels of energy they carry. Laser light energy levels can also be controlled to avoid skin and eye damage. Typical household laser pointers are designed to do no damage to skin. Microwaves carry enough energy to heat surfaces, which is why they are used in microwave ovens. Some sources say that the energy levels found near low-frequency electrical fields by power lines can cause nerves and muscles to respond erratically ### Ionizing radiation - **Alpha decay:** Occurs when the nucleus of a radioactive element, such as uranium, uses the strong nuclear force to release an alpha particle. Alpha particles occur naturally, yet have enough energy to participate in nuclear reactions. Alpha particles are exactly the same as helium nuclei, containing two protons and two neutrons each. - **Beta decay:** When an unstable atom spontaneously decays or transforms, its nucleus releases a beta particle and a neutrino. The beta particle can be either a positively charged particle (positron) or a negatively charged beta particle similar to an electron. The neutrino released is electrically neutral. This process occurs when the nucleus of an atom has either too many protons or too many neutrons. The weak nuclear force then causes a neutron to be converted into a proton (or vice versa) in order to become stable. In general, beta particles are a form of ionizing radiation. There are some low-energy beta particles that do not cause ionization, however. **Gamma radiation** is a form of ionizing radiation, and thus produces a chemical change in the substance through which it passes. Elements with high atomic numbers such as lead have the density to be able to absorb gamma rays and prevent them from penetrating. Note, however, that attenuation coefficients can vary with atomic number. Researchers need to take into account more than just atomic number to determine whether an element will block gamma rays. All forms of ionizing radiation can destroy or cause damage to DNA in cells. Large doses of ionizing radiation have been shown to cause mutations in radiation victims' descendants ### Sources of radiation There are two types of radiation sources: - **Natural source** - **Artificial source** **Natural sources of ionization radiation:** The biosphere is situated in the field of radiation that has existed for millions of years. This field consists basically of two sources - extraterrestrial (cosmic) and terrestrial. The components of the natural radioactive background are the natural radioactivity of ground, natural activity of atmosphere, natural radioactivity of water, and cosmic radiation. A typical value of the effective dose obtained by an individual from the natural radioactive background is about 2.5 mSv annually. Generally, the most significant impact on the radiation exposure comes from natural sources of gaseous radon and its daughter products. This radioactive gas that occurs in nature together with uranium and thorium ores, decays by alpha decay and is dangerous in breathing as it causes internal irradiation. Radon has the largest impact on the exposure of inhabitants in such houses and flats that are built on improper soils The natural sources of radiation are: - Cosmic radiation - Radiation with terrestrial origin - Internal contamination - Radon and its daughter products **Artificial sources of ionization radiation** The radiation background has been increased artificially due to the evolution of civilization.