{"id":18265,"date":"2020-06-27T20:54:46","date_gmt":"2020-06-27T20:54:46","guid":{"rendered":"https:\/\/www.radiation-dosimetry.org\/o-que-e-coeficiente-de-atenuacao-linear-definicao\/"},"modified":"2020-07-24T10:51:37","modified_gmt":"2020-07-24T10:51:37","slug":"o-que-e-coeficiente-de-atenuacao-linear-definicao","status":"publish","type":"post","link":"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-coeficiente-de-atenuacao-linear-definicao\/","title":{"rendered":"O que \u00e9 coeficiente de atenua\u00e7\u00e3o linear &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-u-clearfix su-u-trim\"><span>A soma das tr\u00eas se\u00e7\u00f5es parciais \u00e9 denominada coeficiente de atenua\u00e7\u00e3o linear.\u00a0Atenua\u00e7\u00e3o de raios gama.\u00a0Dosimetria de Radia\u00e7\u00e3o<\/span><\/div>\n<\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-60 lgc-tablet-grid-60 lgc-mobile-grid-100 lgc-equal-heights  lgc-first\">\n<div class=\"inside-grid-column\"><span>A se\u00e7\u00e3o transversal total da intera\u00e7\u00e3o de raios gama com um \u00e1tomo \u00e9 igual \u00e0 soma das tr\u00eas se\u00e7\u00f5es parciais mencionadas:\u00a0<\/span><strong><span>\u03c3 = \u03c3\u00a0<\/span><sub><span>f<\/span><\/sub><span>\u00a0+ \u03c3\u00a0<\/span><sub><span>C<\/span><\/sub><span>\u00a0+ \u03c3\u00a0<\/span><sub><span>p\u00a0<\/span><\/sub><\/strong><\/p>\n<ul>\n<li><strong><span>\u03c3\u00a0<\/span><sub><span>f<\/span><\/sub><span>\u00a0&#8211; Efeito fotoel\u00e9trico<\/span><\/strong><\/li>\n<\/ul>\n<ul>\n<li><strong><span>\u03c3\u00a0<\/span><sub><span>C<\/span><\/sub><span>\u00a0&#8211; espalhamento de Compton<\/span><\/strong><\/li>\n<\/ul>\n<ul>\n<li><strong><span>\u03c3\u00a0<\/span><sub><span>p<\/span><\/sub><span>\u00a0&#8211; Produ\u00e7\u00e3o em pares<\/span><\/strong><\/li>\n<\/ul>\n<p><span>Dependendo da energia dos raios gama e do material absorvedor, uma das tr\u00eas se\u00e7\u00f5es parciais pode se tornar muito maior que as outras duas.\u00a0Em pequenos valores de energia de raios gama, o\u00a0<\/span><strong><span>efeito fotoel\u00e9trico<\/span><\/strong><span>\u00a0domina.\u00a0<\/span><strong><span>A dispers\u00e3o de Compton<\/span><\/strong><span>\u00a0domina em energias intermedi\u00e1rias.\u00a0A dispers\u00e3o de comptons tamb\u00e9m aumenta com a diminui\u00e7\u00e3o do n\u00famero at\u00f4mico de mat\u00e9ria; portanto, o intervalo de domina\u00e7\u00e3o \u00e9 maior para os n\u00facleos leves.\u00a0Finalmente,\u00a0<\/span><strong><span>a produ\u00e7\u00e3o de pares el\u00e9tron-p\u00f3sitron<\/span><\/strong><span>\u00a0domina a altas energias. Com base na defini\u00e7\u00e3o da se\u00e7\u00e3o transversal de intera\u00e7\u00e3o, pode-se derivar a depend\u00eancia da intensidade dos raios gama na espessura do material absorvente.\u00a0Se\u00a0<\/span><strong><span>raios gama monoenerg\u00e9ticos<\/span><\/strong><span>\u00a0s\u00e3o colimados em um\u00a0<\/span><strong><span>feixe estreito<\/span><\/strong><span>e se o detector atr\u00e1s do material detectar apenas os raios gama que passaram por ele sem nenhum tipo de intera\u00e7\u00e3o com esse material, a depend\u00eancia dever\u00e1 ser uma\u00a0<\/span><strong><span>atenua\u00e7\u00e3o exponencial<\/span><\/strong><span>\u00a0simples\u00a0<strong>dos raios gama<\/strong>\u00a0.\u00a0Cada uma dessas intera\u00e7\u00f5es remove o f\u00f3ton do feixe por absor\u00e7\u00e3o ou dispers\u00e3o na dire\u00e7\u00e3o do detector.\u00a0Portanto, as intera\u00e7\u00f5es podem ser caracterizadas por uma probabilidade fixa de ocorr\u00eancia por unidade de comprimento do caminho no absorvedor.\u00a0A soma dessas probabilidades \u00e9 chamada de\u00a0<\/span><strong><span>coeficiente de atenua\u00e7\u00e3o linear<\/span><\/strong><span>\u00a0:<\/span><\/p>\n<p><strong><span>\u03bc = \u03c4\u00a0<\/span><sub><span>(fotoel\u00e9trico)<\/span><\/sub><span>\u00a0+ \u03c3\u00a0<\/span><sub><span>(Compton)<\/span><\/sub><span>\u00a0+ \u03ba\u00a0<\/span><sub><span>(par)<\/span><\/sub><\/strong><\/p>\n<h2><span>Coeficiente de atenua\u00e7\u00e3o linear<\/span><\/h2>\n<p><span>A atenua\u00e7\u00e3o da radia\u00e7\u00e3o gama pode ser descrita pela seguinte equa\u00e7\u00e3o.<\/span><\/p>\n<p><strong><span>I = I\u00a0<\/span><sub><span>0<\/span><\/sub><span>\u00a0.e\u00a0<\/span><sup><span>-\u03bcx<\/span><\/sup><\/strong><\/p>\n<p><span>, onde I \u00e9 a intensidade ap\u00f3s a atenua\u00e7\u00e3o, I\u00a0<\/span><sub><span>o<\/span><\/sub><span>\u00a0\u00e9 a intensidade do incidente, \u03bc \u00e9 o coeficiente de atenua\u00e7\u00e3o linear (cm\u00a0<\/span><sup><span>-1<\/span><\/sup><span>\u00a0) e a espessura f\u00edsica do absorvedor (cm).<\/span><\/p>\n<p><span>Os materiais listados na tabela ao lado s\u00e3o ar, \u00e1gua e elementos diferentes do carbono (\u00a0<\/span><i><span>Z<\/span><\/i><span>\u00a0= 6) ao chumbo (\u00a0<\/span><i><span>Z<\/span><\/i><span>\u00a0= 82) e seus coeficientes de atenua\u00e7\u00e3o linear s\u00e3o dados para tr\u00eas energias de raios gama.\u00a0Existem duas caracter\u00edsticas principais do coeficiente de atenua\u00e7\u00e3o linear:<\/span><\/p>\n<ul>\n<li><span>O coeficiente de atenua\u00e7\u00e3o linear aumenta \u00e0 medida que o n\u00famero at\u00f4mico do absorvedor aumenta.<\/span><\/li>\n<li><span>O coeficiente de atenua\u00e7\u00e3o linear para todos os materiais diminui com a energia dos raios gama.<\/span><\/li>\n<\/ul>\n<h2><\/h2>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-40 lgc-tablet-grid-40 lgc-mobile-grid-100 lgc-equal-heights  lgc-last\">\n<div class=\"inside-grid-column\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/exponential-attenuation.png\"><img loading=\"lazy\" class=\"aligncenter size-medium wp-image-11796 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/exponential-attenuation-300x217.png\" alt=\"Atenua\u00e7\u00e3o\" width=\"300\" height=\"217\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/exponential-attenuation-300x217.png\" \/><\/a><span>Depend\u00eancia da intensidade da radia\u00e7\u00e3o gama na espessura do absorvedor.<\/span><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/attenuation.png\"><img loading=\"lazy\" class=\"aligncenter size-medium wp-image-11796 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/attenuation-300x188.png\" alt=\"Atenua\u00e7\u00e3o de raios gama\" width=\"300\" height=\"188\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/attenuation-300x188.png\" \/><\/a><span>A import\u00e2ncia relativa de v\u00e1rios processos de intera\u00e7\u00e3o da radia\u00e7\u00e3o gama com a mat\u00e9ria.<\/span><strong><span>Tabela de coeficientes de atenua\u00e7\u00e3o linear<\/span><\/strong><span>\u00a0(em cm-1) para diferentes materiais com energias de raios gama de 100, 200 e 500 keV.<\/span><\/p>\n<table rules=\"rows\">\n<tbody>\n<tr>\n<td><span>Absorvedor<\/span><\/td>\n<td><span>100 keV<\/span><\/td>\n<td><span>200 keV<\/span><\/td>\n<td><span>500 keV<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Ar<\/span><\/td>\n<td><span>\u00a0 0.000195 \/ cm<\/span><\/td>\n<td><span>\u00a0 0.000159 \/ cm<\/span><\/td>\n<td><span>\u00a0 0.000112 \/ cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>\u00c1gua<\/span><\/td>\n<td><span>0,167 \/ cm<\/span><\/td>\n<td><span>0,136 \/ cm<\/span><\/td>\n<td><span>0,097 \/ cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Carbono<\/span><\/td>\n<td><span>0,335 \/ cm<\/span><\/td>\n<td><span>0,274 \/ cm<\/span><\/td>\n<td><span>0.196 \/ cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Alum\u00ednio<\/span><\/td>\n<td><span>0.435 \/ cm<\/span><\/td>\n<td><span>0,324 \/ cm<\/span><\/td>\n<td><span>0,227 \/ cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Ferro<\/span><\/td>\n<td><span>2,72 \/ cm<\/span><\/td>\n<td><span>1.09 \/ cm<\/span><\/td>\n<td><span>0.655 \/ cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Cobre<\/span><\/td>\n<td><span>3.8 \/ cm<\/span><\/td>\n<td><span>1,309 \/ cm<\/span><\/td>\n<td><span>0,73 \/ cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Conduzir<\/span><\/td>\n<td><span>59,7 \/ cm<\/span><\/td>\n<td><span>10,15 \/ cm<\/span><\/td>\n<td><span>1,64 \/ cm<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights  lgc-first\">\n<div class=\"inside-grid-column\"><\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \">\n<div class=\"inside-grid-column\"><\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights  lgc-last\">\n<div class=\"inside-grid-column\">\n<h2><\/h2>\n<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p>&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<\/p>\n<p>Este artigo \u00e9 baseado na tradu\u00e7\u00e3o autom\u00e1tica do artigo original em ingl\u00eas. Para mais informa\u00e7\u00f5es, consulte o artigo em ingl\u00eas. Voc\u00ea pode nos ajudar. Se voc\u00ea deseja corrigir a tradu\u00e7\u00e3o, envie-a para: translations@nuclear-power.com ou preencha o formul\u00e1rio de tradu\u00e7\u00e3o on-line. Agradecemos sua ajuda, atualizaremos a tradu\u00e7\u00e3o o mais r\u00e1pido poss\u00edvel. Obrigado.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A soma das tr\u00eas se\u00e7\u00f5es parciais \u00e9 denominada coeficiente de atenua\u00e7\u00e3o linear.\u00a0Atenua\u00e7\u00e3o de raios gama.\u00a0Dosimetria de Radia\u00e7\u00e3o A se\u00e7\u00e3o transversal total da intera\u00e7\u00e3o de raios gama com um \u00e1tomo \u00e9 igual \u00e0 soma das tr\u00eas se\u00e7\u00f5es parciais mencionadas:\u00a0\u03c3 = \u03c3\u00a0f\u00a0+ \u03c3\u00a0C\u00a0+ \u03c3\u00a0p\u00a0 \u03c3\u00a0f\u00a0&#8211; Efeito fotoel\u00e9trico \u03c3\u00a0C\u00a0&#8211; espalhamento de Compton \u03c3\u00a0p\u00a0&#8211; Produ\u00e7\u00e3o em pares Dependendo da &#8230; <a title=\"O que \u00e9 coeficiente de atenua\u00e7\u00e3o linear &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-coeficiente-de-atenuacao-linear-definicao\/\" aria-label=\"More on O que \u00e9 coeficiente de atenua\u00e7\u00e3o linear &#8211; Defini\u00e7\u00e3o\">Ler mais<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[51],"tags":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v15.4 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>O que \u00e9 coeficiente de atenua\u00e7\u00e3o linear - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"A soma das tr\u00eas se\u00e7\u00f5es parciais \u00e9 denominada coeficiente de atenua\u00e7\u00e3o linear. 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