{"id":12705,"date":"2016-09-23T13:37:57","date_gmt":"2016-09-23T13:37:57","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=12705"},"modified":"2022-10-18T10:32:10","modified_gmt":"2022-10-18T10:32:10","slug":"shielding-of-ionizing-radiation","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/","title":{"rendered":"Shielding of Ionizing Radiation"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"su-quote su-quote-style-default\"><div   id="8n9s8rpp6h"    class=\"su-quote-inner su-u-clearfix su-u-trim\"><strong>Shielding of ionizing radiation<\/strong> means having <strong>some material between the source of radiation and you<\/strong> (or some device) that will <strong>absorb the <a title=\"Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/\">radiation<\/a><\/strong>. <strong>Radiation shielding<\/strong> usually consists of barriers of lead, concrete, or water. Many materials can be used for radiation shielding, but there are many situations in radiation protection. It highly depends on the type of radiation to be shielded, its energy, and many other parameters. For example, even depleted uranium can be used as good protection from gamma radiation, but on the other hand, uranium is inappropriate <a title=\"Shielding of Neutron Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/shielding-neutron-radiation\/\">shielding of neutron radiation<\/a>.<\/div><\/div>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/shielding_radiation.png\"><img loading=\"lazy\" class=\"alignright wp-image-12726\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/shielding_radiation-559x1024.png\" alt=\"Shielding of Ionizing Radiation\" width=\"469\" height=\"859\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/shielding_radiation-559x1024.png 559w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/shielding_radiation-164x300.png 164w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/shielding_radiation.png 1200w\" sizes=\"(max-width: 469px) 100vw, 469px\" \/><\/a>Radiation shielding means having <strong>some material between the source of radiation and you<\/strong> (or some device) that will <strong>absorb the <a title=\"Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/\">radiation<\/a><\/strong>. The amount of shielding required, the type of material of shielding strongly depends on several factors. We are not talking about any optimization.<\/p>\n<p>In fact, in some cases, inappropriate shielding may even worsen the radiation situation instead of protecting people from the ionizing radiation. \u00a0Basic factors, which have to be considered during the proposal of radiation shielding, are:<\/p>\n<ul>\n<li>Type of the ionizing radiation to be shielded<\/li>\n<li>The energy spectrum of the ionizing radiation<\/li>\n<li>Length of exposure<\/li>\n<li>Distance from the source of the ionizing radiation<\/li>\n<li>Requirements on the attenuation of the ionizing radiation &#8211; ALARA or ALARP principles<\/li>\n<li>Design degree of freedom<\/li>\n<li>Other physical requirements (e.g.,, transparence in case of leaded glass screens)<\/li>\n<\/ul>\n<p>See also: <a title=\"Interaction of Radiation with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/\">Interaction of Radiation with Matter<\/a><\/p>\n<p>See also: <a href=\"https:\/\/www.radiation-dosimetry.org\/what-is-shielding-of-ionizing-radiation-definition\/\">Shielding of Ionizing Radiation<\/a><\/p>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dashed\" style=\"margin:20px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Principles of Radiation Protection<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<p>Radiation protection is the science and practice of protecting people and the environment from the harmful effects of ionizing radiation. It is a serious topic not only in <a title=\"Nuclear Power Plant\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/\">nuclear power plants<\/a> but also in industry or medical centers. In radiation protection, there are three ways how to protect people from identified radiation sources:<\/p>\n<ul>\n<li><strong>Limiting Time.<\/strong> The amount of radiation exposure depends directly (linearly)<strong> on the time<\/strong> people spend near the radiation source. The dose can be <strong>reduced by limiting exposure time<\/strong>.<\/li>\n<li><strong>Distance.<\/strong> The amount of radiation exposure depends on the distance from the source of radiation. Like heat from a fire, if you are too close, the intensity of heat radiation is high, and you can get burned. If you are at the right distance, you can withstand there without any problems and are comfortable. If you are too far from the heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from radiation sources.<\/li>\n<li><strong>Shielding.<\/strong> Finally, if the source is too intensive and time or distance does not provide sufficient radiation protection, the shielding must be used. Radiation shielding usually consists of barriers of lead, concrete, or water. Many materials can be used for radiation shielding, but there are many situations in radiation protection. It highly depends on the type of radiation to be shielded, its energy, and many other parameters. For example, even depleted uranium can be used as good protection from gamma radiation, but on the other hand, uranium is absolutely inappropriate <a title=\"Shielding of Neutron Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/shielding-neutron-radiation\/\">shielding of neutron radiation<\/a>.<\/li>\n<\/ul>\n<figure id=\"attachment_12696\" aria-describedby=\"caption-attachment-12696\" style=\"width: 890px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/radiation_protection_principles.gif\"><img loading=\"lazy\" class=\"size-full wp-image-12696\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/radiation_protection_principles.gif\" alt=\"radiation protection pronciples - time, distance, shielding\" width=\"900\" height=\"700\" \/><\/a><figcaption id=\"caption-attachment-12696\" class=\"wp-caption-text\">Principles of Radiation Protection &#8211; Time, Distance, Shielding<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<\/div><\/div>\n<div   id="8n9s8rpp6h"    class=\"collapsible-container\">\n<h2>Shielding of Radiation in Nuclear Power Plants<\/h2>\n<p>Generally, in the nuclear industry, radiation shielding has many purposes. In <a title=\"Nuclear Power Plant\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/\">nuclear power plants<\/a>, the main purpose is <strong>to reduce the radiation exposure<\/strong> to persons and staff in the vicinity of radiation sources. In NPPs, the main source of radiation is conclusively <a title=\"Nuclear Reactor\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/\">the nuclear reactor<\/a> and its <a title=\"Reactor Core\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor-core\/\">reactor core<\/a>. Nuclear reactors are, in general, powerful sources of an entire spectrum of<a title=\"Forms of Ionizing Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/forms-ionizing-radiation\/\"> types of ionizing radiation<\/a>. Shielding used for this purpose is called <strong>biological shielding<\/strong>.<\/p>\n<p>But this is not the only purpose of radiation shielding. Shields are also used in some reactors to reduce the intensity of <a title=\"Gamma Rays \/ Gamma Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gamma rays <\/a>or <a title=\"Neutron\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/\">neutrons<\/a> incident on the reactor vessel. This radiation shielding protects the reactor vessel and its internals (e.g.,, the <a title=\"Core Barrel\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/core-barrel\/\">core support barrel<\/a>) from excessive heating due to gamma-ray absorption fast neutron <a title=\"Neutron moderator\" href=\"http:\/\/sitepourvtc.com\/neutron-moderator\/\">moderation<\/a>. Such shields are usually referred to as\u00a0<strong>thermal shields<\/strong>.<\/p>\n<p>See also: <a title=\"Neutron Reflector\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/neutron-reflector\/\">Neutron Reflector<\/a>.<\/p>\n<p>A little strange radiation shielding is usually used to protect the material of reactor pressure vessels (especially in <a title=\"PWR \u2013 Pressurized water reactor\" href=\"http:\/\/sitepourvtc.com\/pwr-pressurized-water-reactor\/\">PWR power plants<\/a>). Structural materials of pressure vessels and reactor internals are damaged, especially by <strong>fast neutrons<\/strong>. Fast neutrons create structural defects, which in result lead to <strong>embrittlement of material of pressure vessel<\/strong>. To minimize the neutron flux at the vessel wall, also core loading strategy can be modified. In the &#8220;out-in&#8221; fuel loading strategy, fresh fuel assemblies are placed at the periphery of the core. \u00a0This configuration causes high neutron fluence at the vessel wall. Therefore, many nuclear power plants have adopted the &#8220;in-out&#8221; fuel loading strategy (with<strong> low leakage loading patterns &#8211; L3P<\/strong>). In contrast to the &#8220;out-in&#8221; strategy, low leakage cores have fresh fuel assemblies in the second row, not at the periphery of the core. The periphery contains fuel with higher fuel burnup and lowers relative power, and a very sophisticated radiation shield.<\/p>\n<p>In nuclear power plants, the central problem is to shield against <strong>gamma rays<\/strong> and <strong>neutrons<\/strong> because the ranges of charged particles (such as beta particles and alpha particles) in the matter are very short. On the other hand, we must deal with shielding all types of radiation because each nuclear reactor is a significant source of all types of ionizing radiation.<\/p>\n<h2>Shielding of various types of radiation<\/h2>\n<div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Shielding of Alpha Radiation<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<h3>Shielding of Alpha Radiation<\/h3>\n<figure id=\"attachment_11672\" aria-describedby=\"caption-attachment-11672\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-11672\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber-300x156.jpg\" alt=\"Alpha Particle - Cloud Chamber\" width=\"300\" height=\"156\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber-300x156.jpg 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber-1024x535.jpg 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber.jpg 1162w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-11672\" class=\"wp-caption-text\">Alpha particles and electrons (deflected by a magnetic field) from a thorium rod in a cloud chamber.<br \/>Source: wikipedia.org<\/figcaption><\/figure>\n<p>The\u00a0following\u00a0features of alpha particles are crucial in their shielding.<\/p>\n<ul>\n<li><a title=\"Alpha Particle\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/alpha-particle\/\"><strong>Alpha particles<\/strong><\/a> are energetic <strong>nuclei of helium,<\/strong> and they\u00a0are relatively heavy\u00a0and carry a <strong>double positive charge<\/strong>.<\/li>\n<li>Alpha particles <a title=\"Interaction of Heavy Charged Particles with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-heavy-charged-particles\/\">interact with matter<\/a> primarily through <strong>coulomb forces<\/strong> (ionization and excitation of matter) between their electrons&#8217; positive and negative charge of the electrons from atomic orbitals.<\/li>\n<li>Alpha particles <strong>heavily ionize matter<\/strong>, and they quickly lose their kinetic energy. On the other hand, they deposit all their energies along their short paths.<\/li>\n<li>The <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-heavy-charged-particles\/stopping-power-bethe-formula\/\">Bethe formula<\/a> well describes the stopping power.<\/li>\n<\/ul>\n<p>The stopping power of most materials is very high for alpha particles and heavy-charged particles. Therefore alpha particles have <strong>very short ranges<\/strong>. For example, the ranges of a 5 MeV alpha particle (most have such initial energy) are approximately 0,002 cm in aluminium alloy or approximately 3.5 cm in air. A thin piece of paper can stop most alpha particles<strong><span style=\"font-weight: 400;\">. Even the dead cells in the outer layer of human skin provide adequate shielding because alpha particles can&#8217;t penetrate it.\u00a0<\/span><\/strong><\/p>\n<p>Therefore the shielding of alpha radiation alone does not pose a difficult problem. On the other hand, alpha radioactive nuclides can lead to serious health hazards when ingested or inhaled (internal contamination). When they are ingested or inhaled, the alpha particles from their decay significantly harm the internal living tissue. Moreover, pure alpha radiation is very rare. Alpha decay is frequently accompanied by gamma radiation which shielding is another issue.<\/p>\n<p>See also: <a title=\"Shielding of Alpha Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-of-alpha-radiation\/\">Shielding of Alpha Radiation<\/a>.<\/p>\n<p>See also: <a title=\"Interaction of Heavy Charged Particles with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-heavy-charged-particles\/\">Interaction of Heavy Charged Particles with Matter<\/a><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Shielding of Beta Radiation<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<h3>Shielding of Beta Radiation<\/h3>\n<figure id=\"attachment_11672\" aria-describedby=\"caption-attachment-11672\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-11672\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber-300x156.jpg\" alt=\"Alpha Particle - Cloud Chamber\" width=\"300\" height=\"156\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber-300x156.jpg 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber-1024x535.jpg 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/Alpha_particle_cloud_chamber.jpg 1162w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-11672\" class=\"wp-caption-text\">Alpha particles and electrons (deflected by a magnetic field) from a thorium rod in a cloud chamber.<br \/>Source: wikipedia.org<\/figcaption><\/figure>\n<p>The\u00a0following\u00a0features of beta\u00a0particles (electrons) are crucial in their shielding.<\/p>\n<ul>\n<li><b><a title=\"Beta Particle\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/\">Beta particles<\/a>\u00a0<\/b>are energetic electrons. They are relatively light and carry a <strong>single\u00a0negative\u00a0charge<\/strong>.<\/li>\n<li>Their mass is equal to the mass of the orbital electrons with which they are interacting. A much larger fraction of its kinetic energy can be lost in a single interaction than the alpha particle.<\/li>\n<li>Their path is not so straightforward. The beta particles follow a very <strong>zig-zag path<\/strong> through absorbing material. This resulting path of the particle is longer than the linear penetration (range) into the material.<\/li>\n<li>Since they have very low\u00a0mass, beta particles reach <strong>mostly relativistic energies.<\/strong><\/li>\n<li>Beta particles differ from other heavy charged particles in the fraction of energy lost by the radiative process known as the <a title=\"Bremsstrahlung\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/bremsstrahlung-2\/\"><strong>bremsstrahlung<\/strong><\/a>. Therefore for high energy, beta radiation shielding dense materials are inappropriate.<\/li>\n<li>When the beta particle moves faster than the speed of light (phase velocity) in the material, it generates a shock wave of electromagnetic radiation known as the<a title=\"Cherenkov Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/cherenkov-radiation\/\"><strong> Cherenkov radiation<\/strong><\/a>.<\/li>\n<\/ul>\n<p>Beta radiation\u00a0ionizes matter weaker than <a title=\"Alpha Particle\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/alpha-particle\/\">alpha radiation<\/a>. On the other hand, the <strong>ranges of beta particles are longer<\/strong> and depend strongly on the initial kinetic energy of the particle. Some have enough energy to be of concern regarding external exposure. A 1 MeV beta particle can travel approximately 3.5 meters in the air. Such beta particles can penetrate the body and deposit dose to internal structures near the surface. Therefore greater shielding than in the case of alpha radiation is required.<\/p>\n<p>Materials with <strong>low atomic number Z<\/strong> are appropriate as beta particle shields. With high Z materials, <a title=\"Bremsstrahlung\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/bremsstrahlung-2\/\">the bremsstrahlung<\/a> (secondary radiation &#8211; X-rays) is associated. This radiation is created during the slowing down of beta particles while they travel in a very dense medium. Heavy clothing, thick cardboard, or a thin aluminium plate will protect from beta radiation and prevent bremsstrahlung production. Lead and plastic are commonly used to shield beta radiation. Radiation protection literature is ubiquitous in advising plastic placement first to absorb all the beta particles before any lead shielding is used. This advice is based on the well-established theory that radiative losses (bremsstrahlung production) are more prevalent in higher atomic number (Z) materials than low Z materials.<\/p>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-beta-radiation\/\">Shielding of Beta Radiation<\/a>.<\/p>\n<p>See also more theory: <a title=\"Interaction of Beta Radiation with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-beta-radiation\/\">Interaction of Beta\u00a0Radiation with Matter<\/a><\/p>\n<p>See also calculator: <a title=\"Rad Pro Calculator\" href=\"http:\/\/www.radprocalculator.com\/Beta.aspx\">Beta\u00a0activity to dose rate\u00a0<\/a><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Shielding of Positrons<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<h3>Shielding of Positrons<\/h3>\n<p>See first: <a title=\"Shielding of Beta Radiation \u2013 Electrons\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-beta-radiation\/\">Shielding of Beta Radiation &#8211; Electrons<\/a><\/p>\n<figure id=\"attachment_11717\" aria-describedby=\"caption-attachment-11717\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/positron-annihilation.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11717\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/positron-annihilation-300x165.png\" alt=\"positron annihilation\" width=\"300\" height=\"165\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/positron-annihilation-300x165.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/positron-annihilation-1024x564.png 1024w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/positron-annihilation.png 1327w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-11717\" class=\"wp-caption-text\">When a positron (antimatter particle) comes to rest, it interacts with an electron, resulting in the annihilation of both particles and the complete conversion of their rest mass to pure energy in the form of two oppositely directed 0.511 MeV photons.<\/figcaption><\/figure>\n<p><strong>The coulomb forces<\/strong> that constitute the major mechanism of energy loss for electrons are present for either positive or negative charge on the particle and constitute the major mechanism of energy loss also for positrons. Whatever the interaction involves a repulsive or attractive force between the incident particle and orbital electron (or atomic nucleus), the impulse and energy transfer for particles of equal mass\u00a0<strong>are about the same<\/strong>. Therefore <strong>positrons interact similarly<\/strong> with the matter <strong>when they are energetic<\/strong>. The track of positrons in a material is similar to the track of electrons. <strong>Even their specific energy loss<\/strong> and range <strong>are about the same<\/strong> for equal initial energies.<\/p>\n<p><strong>At the end of their path<\/strong>,<strong> positrons differ significantly<\/strong> from electrons. When a positron (antimatter particle) comes to rest, it interacts with an electron (matter particle), resulting in <a title=\"Positron Annihilation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/positron-annihilation-2\/\"><strong>the annihilation<\/strong><\/a> of both particles and the complete conversion of their rest mass <strong>to pure energy<\/strong> (according to the E=mc<sup>2<\/sup> formula) in the form of two oppositely directed 0.511 MeV <strong><a title=\"Gamma Rays \/ Gamma Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gamma rays<\/a>\u00a0<\/strong>(photons).<\/p>\n<p>Therefore any positron shield has to include also a gamma-ray shield. A multi-layered radiation shield is appropriate to minimize the bremsstrahlung. Material for the first layer must fulfill the requirements for <a title=\"Shielding of Beta Radiation \u2013 Electrons\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-beta-radiation\/\">negative beta radiation shielding<\/a>. The first layer of such a shield may be a thin aluminium plate (to shield positrons), while the second layer of such a shield may be a dense material such as lead or depleted uranium.<\/p>\n<p>See also: <a title=\"Interaction of Beta Radiation with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-beta-radiation\/\">Interaction of Beta Radiation with Matter<\/a><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Shielding of Gamma Radiation<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<h3>Characteristics of Gamma Rays<\/h3>\n<figure id=\"attachment_11684\" aria-describedby=\"caption-attachment-11684\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/total_photon_attenuation.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11684\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/total_photon_attenuation-300x217.png\" alt=\"Attenuation coefficients.\" width=\"300\" height=\"217\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/total_photon_attenuation-300x217.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/03\/total_photon_attenuation.png 900w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-11684\" class=\"wp-caption-text\">Total photon cross-sections.<br \/>Source: Wikimedia Commons<\/figcaption><\/figure>\n<p><strong>Key features of <a title=\"Gamma Rays \/ Gamma Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gamma rays<\/a><\/strong> are summarized in the following few points:<\/p>\n<ul>\n<li>Gamma rays are <strong>high-energy photons<\/strong> (about 10 000 times as much energy as the visible photons), the same <a title=\"Photon \u2013 Fundamental Particle\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/\">photons<\/a> as the photons forming the visible range of the electromagnetic spectrum &#8211; light.<\/li>\n<li>Photons (gamma rays and X-rays) can ionize atoms directly (despite they are electrically neutral) through the Photoelectric effect and the Compton effect, but secondary (indirect) ionization is much more significant.<\/li>\n<li>Gamma rays ionize matter primarily via <strong>indirect ionization<\/strong>.<\/li>\n<li>Although many possible interactions are known, there are three key interaction mechanisms with the matter.\n<ul>\n<li><a title=\"Photoelectric Effect\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-gamma-radiation-matter\/photoelectric-effect\/\"><strong>Photoelectric effect<\/strong><\/a><\/li>\n<li><a title=\"Compton Scattering\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-gamma-radiation-matter\/compton-scattering\/\"><strong>Compton scattering<\/strong><\/a><\/li>\n<li><a title=\"Positron-Electron Pair Production\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-gamma-radiation-matter\/pair-production\/\"><strong>Pair production<\/strong><\/a><\/li>\n<\/ul>\n<\/li>\n<li>Gamma rays travel <strong>at the speed of light,<\/strong> and they can travel thousands of meters in the air before spending their energy.<\/li>\n<li>Since gamma radiation is very penetrating, it must be shielded by very dense materials, such as lead or uranium.<\/li>\n<li>The distinction between X-rays and gamma rays is not so simple and has changed in recent decades. \u00a0According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while <b>the nucleus emits gamma rays<\/b>.<\/li>\n<li>Gamma rays frequently <strong>accompany the emission<\/strong> of <a title=\"Alpha Particle\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/alpha-particle\/\">alpha<\/a> and <a title=\"Beta Particle\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/\">beta radiation<\/a>.<\/li>\n<\/ul>\n<h3>Shielding of Gamma Radiation<\/h3>\n<p>In short, effective shielding of gamma radiation is in most cases based on the use of materials with two following material properties:<\/p>\n<ul>\n<li><strong><span style=\"font-weight: 400;\">high-density of material.\u00a0<\/span><\/strong><\/li>\n<li><strong><span style=\"font-weight: 400;\">the high atomic number of material \u00a0(high Z materials)<\/span><\/strong><\/li>\n<\/ul>\n<p><strong><span style=\"font-weight: 400;\">However, low-density materials and low Z materials can be compensated with increased thickness, which is as significant as density and atomic number in shielding applications.\u00a0\u00a0<\/span><\/strong><\/p>\n<p><strong><span style=\"font-weight: 400;\">A lead is widely used as a gamma shield.\u00a0 The major advantage of the lead shield is its compactness due to its higher density. On the other hand, <a title=\"Depleted Uranium\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-fuel\/uranium\/depleted-uranium\/\">depleted uranium<\/a> is much more effective due to its higher Z.\u00a0\u00a0Depleted uranium shields in portable gamma-ray sources.\u00a0<\/span><\/strong><\/p>\n<p>In <a title=\"Nuclear Power Plant\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/\">nuclear power plants<\/a>,\u00a0shielding of a <a title=\"Reactor Core\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor-core\/\">reactor core<\/a> can be provided by materials of reactor pressure vessel, reactor internals (<a title=\"Neutron Reflector\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor\/neutron-reflector\/\">neutron reflector<\/a>). Also, heavy concrete is usually used to shield both <a title=\"Shielding of Neutron Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/shielding-neutron-radiation\/\">neutrons<\/a> and gamma radiation.<\/p>\n<p>Although water is neither high density nor high Z material, it is commonly used as gamma shields. Water provides a radiation shielding of fuel assemblies in a spent fuel pool during storage or transports from and into the <a title=\"Reactor Core\" href=\"http:\/\/sitepourvtc.com\/nuclear-power-plant\/nuclear-reactor-core\/\">reactor core<\/a>.<\/p>\n<p>In general, gamma radiation shielding is more complex and difficult than <a title=\"Shielding of Alpha Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-of-alpha-radiation\/\">alpha<\/a> or <a title=\"Shielding of Beta Radiation \u2013 Electrons\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-beta-radiation\/\">beta radiation shielding<\/a>. To comprehensively understand how a gamma-ray loses its initial energy, how it can be attenuated, and how it can be shielded, we must have detailed knowledge of its interaction mechanisms.<\/p>\n<p>See also: <a title=\"Shielding of Gamma Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-gamma-radiation\/\">Shielding of Gamma Radiation<\/a>.<\/p>\n<p>See also more theory: <a title=\"Interaction of Gamma Radiation with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-gamma-radiation-matter\/\">Interaction of Gamma Radiation with Matter<\/a><\/p>\n<p>See also calculator: G<a title=\"Rad Pro Calculator\" href=\"http:\/\/www.radprocalculator.com\/Gamma.aspx\">amma activity to dose rate (with\/without shield)<\/a><\/p>\n<p>See also XCOM &#8211; photon cross-section DB: <a title=\"XCOM Database\" href=\"http:\/\/www.nist.gov\/pml\/data\/xcom\/\">XCOM: Photon Cross Sections Database<\/a><\/div><\/div>\n<div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>Shielding of Neutron Radiation<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\">There are three main features of neutrons, which are crucial in the shielding of neutrons.<\/p>\n<ul>\n<li>Neutrons have <strong>no net electric charge<\/strong>. Therefore they cannot be affected or stopped by electric forces. Neutrons ionize matter only indirectly, which makes neutrons highly penetrating types of radiation.<\/li>\n<li>Neutrons scatter with heavy nuclei <strong>very elastically<\/strong>. Heavy nuclei very hard slow down a neutron, let alone absorb a fast neutron.<\/li>\n<li>An absorption of neutron (one would say shielding) causes the initiation of certain <a title=\"Interactions of Neutrons with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/interactions-neutrons-matter\/\" target=\"_blank\" rel=\"noopener\">nuclear reactions<\/a> (capture, rearrangement, or even<a title=\"Nuclear Fission\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/fission\/\" target=\"_blank\" rel=\"noopener\"> fission<\/a>), accompanied by many other <a title=\"Forms of Ionizing Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/forms-ionizing-radiation\/\" target=\"_blank\" rel=\"noopener\">types of radiation<\/a>. In short, only neutrons make matter radioactive. Therefore with neutrons, we have to shield also the other types of radiation.<\/li>\n<\/ul>\n<p>The best materials for shielding neutrons must be able to:<\/p>\n<ul>\n<li><strong>Slow down neutrons<\/strong> (the same principle as\u00a0<a title=\"Neutron moderator\" href=\"http:\/\/sitepourvtc.com\/neutron-moderator\/\" target=\"_blank\" rel=\"noopener\">neutron moderation<\/a>). The first point can be fulfilled only by a material containing <strong>light hydrogen atoms<\/strong>, such as water, polyethylene, and concrete. The nucleus of a hydrogen nucleus contains only a proton. Since a proton and a neutron have <strong>almost identical masses<\/strong>, a neutron scattering on a hydrogen nucleus can give up a great amount of its energy (even the entire kinetic energy of a neutron can be transferred to a proton after one collision). This is similar to a billiard. Since a cue ball and another billiard ball have identical masses, the cue ball hitting another ball can be made to stop, and the other ball will start moving with the same velocity. On the other hand, if a ping pong ball is thrown against a bowling ball (neutron vs. heavy nucleus), the ping pong ball will bounce off with very little change in velocity, only a change in direction. Therefore, lead is ineffective for blocking neutron radiation, as neutrons are uncharged and can pass through dense materials.<\/li>\n<li>\n<figure id=\"attachment_381\" aria-describedby=\"caption-attachment-381\" style=\"width: 290px\" class=\"wp-caption alignright\"><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/11\/cross-sections_nuclides.png\"><img loading=\"lazy\" class=\"size-medium wp-image-381\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/11\/cross-sections_nuclides-300x180.png\" alt=\"Table of cross-sections\" width=\"300\" height=\"180\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/11\/cross-sections_nuclides-300x180.png 300w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2014\/11\/cross-sections_nuclides.png 732w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-381\" class=\"wp-caption-text\">Table of cross-sections<\/figcaption><\/figure>\n<p><strong>Absorb this slowed neutron.<\/strong> <strong>Thermal neutrons<\/strong> can be easily absorbed by capture in materials with high neutron capture <a title=\"Neutron cross-section\" href=\"http:\/\/sitepourvtc.com\/neutron-cross-section\/\" target=\"_blank\" rel=\"noopener\">cross-sections<\/a> (thousands of barns) like<a title=\"Boron 10\" href=\"http:\/\/sitepourvtc.com\/glossary\/boron-10\/\"><strong> boron<\/strong><\/a>, lithium, or <a title=\"Cadmium\" href=\"http:\/\/sitepourvtc.com\/glossary\/cadmium\/\">cadmium<\/a>. Generally, only a thin layer of such absorber is sufficient to shield thermal neutrons. Hydrogen (in the form of water), which can be used to slow down neutrons, has an absorption cross-section of 0.3 barns. This is not enough, but this insufficiency can be offset by sufficient thickness of the water shield.<\/li>\n<li><strong>Shield the accompanying radiation<\/strong>. In the case of cadmium shield, the absorption of neutrons is accompanied by <strong>strong emission of gamma rays<\/strong>. Therefore additional shield is necessary <strong>to attenuate the gamma rays<\/strong>. This phenomenon practically does not exist for lithium and is much less important for boron as a neutron absorption material. For this reason, materials containing boron are often used in neutron shields. In addition, boron (in boric acid) is well soluble in water, making this combination a very effective neutron shield.<\/li>\n<\/ul>\n<h2>Water as a neutron shield<\/h2>\n<p>Water, due to the high hydrogen content and availability, <strong>is effective<\/strong> and common <strong>neutron shielding<\/strong>. However, due to the low atomic number of hydrogen and oxygen, water is not a good shield against gamma rays. On the other hand, in some cases, this disadvantage (low density) can be compensated by the high thickness of the water shield. \u00a0In the case of neutrons, water perfectly moderates neutrons, but with the absorption of neutrons by hydrogen nucleus, secondary gamma rays with high energy are produced. These gamma rays highly penetrate matter, and therefore they can increase requirements on the thickness of the water shield. Adding a boric acid can help with this problem (neutron absorption on boron nuclei without strong gamma emission) but results in another problem with corrosion of construction materials.<\/p>\n<h2>Concrete as a neutron shield<\/h2>\n<p>The most commonly used neutron shielding in many nuclear science and engineering sectors is the shield of concrete. Concrete is also <strong>hydrogen-containing<\/strong> material, but unlike water, the concrete has a <strong>higher density<\/strong> (<strong>suitable for secondary gamma shielding<\/strong>) and does not need any maintenance. Because concrete is a mixture of several different materials, its composition is not constant. So when referring to concrete as a neutron shielding material, the material used in its composition should be told correctly. Generally, concrete is divided into <strong>&#8220;ordinary&#8221;<\/strong> concrete and <strong>&#8220;heavy&#8221;<\/strong> concrete. <strong>Heavy concrete<\/strong> uses <strong>heavy natural aggregates<\/strong> such as barites \u00a0(barium sulfate) or magnetite or <strong>manufactured aggregates<\/strong> such as iron, steel balls, steel punch, or other additives. As a result of these additives, heavy concrete has a <strong>higher density<\/strong> than ordinary concrete (~2300 kg\/m<sup>3<\/sup>). Very heavy concrete can achieve density <strong>up to 5,900 kg\/m<sup>3<\/sup><\/strong> with iron additives or <strong>8900 kg\/m<sup>3<\/sup><\/strong> with lead additives. Heavy concrete provides <strong>very effective protection<\/strong> against neutrons.<\/p>\n<p>See also: <a title=\"Shielding of Neutron Radiation\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/shielding-neutron-radiation\/\">Shielding of Neutron Radiation<\/a><\/p>\n<p>See also: <a title=\"Interactions of Neutrons with Matter\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/neutron\/interactions-neutrons-matter\/\">Interaction of Neutrons with Matter<\/a><\/div><\/div><\/div>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div>\n<h2>Calculation of Shielded Dose Rate in Sieverts from Contaminated Surface<\/h2>\n<p>Assume a surface in which <strong>1.0 Ci of 137Cs contaminates.<\/strong> Assume that this <strong>contaminant<\/strong> can be approximated by the <strong>point isotropic source,<\/strong> which contains <strong>1.0 Ci of <sup>137<\/sup>Cs<\/strong>, with a <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/radioactive-decay-law\/half-life\/\">half-life<\/a> of <strong>30.2 years<\/strong>. Note that the relationship between half-life and the amount of a <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/radionuclide-radioisotope\/\">radionuclide<\/a> required to give an activity of <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/radiation-protection\/units-of-radioactivity\/curie-unit-of-radioactivity\/\">one curie<\/a> is shown below. This amount of material can be calculated using \u03bb, which is the <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/radioactive-decay-law\/decay-constant\/\">decay constant<\/a> of certain nuclide:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/07\/Curie-Unit-of-Activity.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-24886\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/07\/Curie-Unit-of-Activity.png\" alt=\"Curie - Unit of Activity\" width=\"378\" height=\"61\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/07\/Curie-Unit-of-Activity.png 378w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/07\/Curie-Unit-of-Activity-300x48.png 300w\" sizes=\"(max-width: 378px) 100vw, 378px\" \/><\/a><\/p>\n<p>About 94.6 percent decays by <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radioactive-decay\/beta-decay-beta-radioactivity\/\">beta emission<\/a> to a metastable <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/atom-properties-of-atoms\/nuclides\/isomers\/\">nuclear isomer<\/a> of barium: barium-137m. The main photon peak of Ba-137m is <strong>662 keV<\/strong>. For this calculation, assume that all decays go through this channel.<\/p>\n<p><strong>Calculate the primary photon dose rate<\/strong>, in sieverts per hour (Sv.h<sup>-1<\/sup>), at the outer surface of a 5 cm thick lead shield. Then <strong>calculate the<\/strong> <strong>equivalent and effective dose rates<\/strong> for two cases.<\/p>\n<ol>\n<li>Assume that this external radiation field penetrates <strong>uniformly <\/strong>through the whole body. That means: Calculate the <strong>effective whole-body dose rate<\/strong>.<\/li>\n<li>Assume that this external radiation field penetrates <strong>only lungs,<\/strong> and the other organs are completely shielded. That means: Calculate the <strong>effective dose rate<\/strong>.<\/li>\n<\/ol>\n<p>Note that, primary photon dose rate neglects all secondary particles. Assume that the effective distance of the source from the dose point is <strong>10 cm<\/strong>. We shall also assume that the dose point is soft tissue and can reasonably be simulated by water, and we use the mass-energy absorption coefficient for water.<\/p>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-gamma-radiation-matter\/gamma-ray-attenuation\/\">Gamma Ray Attenuation<\/a><\/p>\n<p>See also: <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-gamma-radiation\/\">Shielding of Gamma Rays<\/a><\/p>\n<p><strong>Solution:<\/strong><\/p>\n<p>The primary photon dose rate is <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/interaction-radiation-matter\/interaction-gamma-radiation-matter\/gamma-ray-attenuation\/\">attenuated exponentially<\/a>, and the dose rate from primary photons, taking account of the shield, is given by:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/dose-rate-calculation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25304\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/dose-rate-calculation.png\" alt=\"dose rate calculation\" width=\"671\" height=\"307\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/dose-rate-calculation.png 671w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/dose-rate-calculation-300x137.png 300w\" sizes=\"(max-width: 671px) 100vw, 671px\" \/><\/a><\/p>\n<p>As can be seen, we do not account for the buildup of secondary radiation. If secondary particles are produced, or the primary radiation changes its energy or direction, the effective attenuation will be much less. \u00a0This assumption generally underestimates the true dose rate, especially for thick shields and when the dose point is close to the shield surface, but this assumption simplifies all calculations. For this case, the true dose rate (with the buildup of secondary radiation) will be more than two times higher.<\/p>\n<p>To calculate the <strong>absorbed dose rate<\/strong>, we have to use the formula:<\/p>\n<ul>\n<li>k = 5.76 x 10<sup>-7<\/sup><\/li>\n<li>S = 3.7 x 10<sup>10<\/sup> s<sup>-1<\/sup><\/li>\n<li>E = 0.662 MeV<\/li>\n<li>\u03bc<sub>t<\/sub>\/\u03c1 = <sup>\u00a0<\/sup>0.0326 cm<sup>2<\/sup>\/g (values are available at NIST)<\/li>\n<li>\u03bc = \u00a01.289 cm<sup>-1<\/sup> (values are available at NIST)<\/li>\n<li>D = 5 cm<\/li>\n<li>r = 10 cm<\/li>\n<\/ul>\n<p><strong>Result:<\/strong><\/p>\n<p>The resulting absorbed dose rate in grays per hour is then:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation-1.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25319\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation-1.png\" alt=\"absorbed dose rate - gray - calculation\" width=\"551\" height=\"153\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation-1.png 551w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation-1-300x83.png 300w\" sizes=\"(max-width: 551px) 100vw, 551px\" \/><\/a><\/p>\n<p><strong>1) Uniform irradiation<\/strong><\/p>\n<p>Since the <a href=\"http:\/\/sitepourvtc.com\/nuclear-engineering\/radiation-protection\/equivalent-dose\/radiation-weighting-factor\/\">radiation weighting factor<\/a> for <a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gamma rays<\/a> is equal to one, and we have assumed the uniform radiation field (the tissue weighting factor is also equal to unity), we can directly calculate the equivalent dose rate and the effective dose rate (E = H<sub>T<\/sub>) from the absorbed dose rate as:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-uniform.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25478\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-uniform.png\" alt=\"calculation - effective dose - uniform\" width=\"467\" height=\"182\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-uniform.png 467w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-uniform-300x117.png 300w\" sizes=\"(max-width: 467px) 100vw, 467px\" \/><\/a><\/p>\n<p><strong>2) Partial irradiation<\/strong><\/p>\n<p>In this case, we assume partial irradiation of lungs only. Thus, we have to use the <strong>tissue weighting factor<\/strong>, which is equal to <strong>w<sub>T<\/sub> = 0.12<\/strong>. The radiation weighting factor for gamma rays is equal to one. As a result, we can calculate the effective dose rate as:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-non-uniform.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25480\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-non-uniform.png\" alt=\"calculation - effective dose - non-uniform\" width=\"495\" height=\"178\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-non-uniform.png 495w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/11\/calculation-effective-dose-non-uniform-300x108.png 300w\" sizes=\"(max-width: 495px) 100vw, 495px\" \/><\/a><\/p>\n<p>Note that if one part of the body (e.g.,, the lungs) receives a radiation dose, it represents a risk for a particularly damaging effect (e.g.,, lung cancer). If the same dose is given to another organ, it represents a different risk factor.<\/p>\n<p>If we want to account for the buildup of secondary radiation, then we have to include the buildup factor. The <strong>extended formula<\/strong> for the dose rate is then:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25303\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation.png\" alt=\"absorbed dose rate - gray\" width=\"693\" height=\"158\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation.png 693w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2018\/10\/absorbed-dose-rate-gray-calculation-300x68.png 300w\" sizes=\"(max-width: 693px) 100vw, 693px\" \/><\/a><\/p>\n<h2>Buildup Factors for Gamma Rays Shielding<\/h2>\n<p>The <strong>buildup factor<\/strong> is a correction factor that considers the influence of the scattered radiation plus any <strong>secondary particles<\/strong> in the medium during shielding calculations. If we want to account for the buildup of secondary radiation, then we have to include the <strong>buildup factor<\/strong>. The buildup factor is then a multiplicative factor that accounts for the response to the un-collided photons to include the contribution of the scattered photons. Thus, the buildup factor can be obtained as a ratio of the total dose to the response for un-collided dose.<\/p>\n<p>The <strong>extended formula<\/strong> for the dose rate calculation is:<\/p>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2019\/01\/Buildup-Factor-in-Dose-Rate-Calculation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25983\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2019\/01\/Buildup-Factor-in-Dose-Rate-Calculation.png\" alt=\"Buildup Factor\" width=\"689\" height=\"348\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2019\/01\/Buildup-Factor-in-Dose-Rate-Calculation.png 689w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2019\/01\/Buildup-Factor-in-Dose-Rate-Calculation-300x152.png 300w\" sizes=\"(max-width: 689px) 100vw, 689px\" \/><\/a><\/p>\n<p>The ANSI\/ANS-6.4.3-1991 Gamma-Ray Attenuation Coefficients and Buildup Factors for Engineering Materials Standard, contains derived gamma-ray attenuation coefficients and buildup factors for selected engineering materials and elements for use in shielding calculations (ANSI\/ANS-6.1.1, 1991).<\/p>\n<\/div>\n<div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:20px 0;border-width:2px;border-color:#999999\"><\/div>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See previous:<\/h2>\n<a href=\"\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Radiation<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See next:<\/h2>\n<a href=\"\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Radiation shielding means having some material between the source of radiation and you (or some device) that will absorb the radiation. The amount of shielding required, the type of material of shielding strongly depends on several factors. We are not talking about any optimization. In fact, in some cases, inappropriate shielding may even worsen the &#8230; <a title=\"Shielding of Ionizing Radiation\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/\" aria-label=\"More on Shielding of Ionizing Radiation\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":11325,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12705"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=12705"}],"version-history":[{"count":5,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12705\/revisions"}],"predecessor-version":[{"id":31309,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12705\/revisions\/31309"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/11325"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=12705"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}