{"id":18068,"date":"2020-06-26T15:45:03","date_gmt":"2020-06-26T15:45:03","guid":{"rendered":"https:\/\/www.radiation-dosimetry.org\/o-que-e-metade-da-camada-de-valor-raios-x-definicao\/"},"modified":"2020-07-24T05:32:47","modified_gmt":"2020-07-24T05:32:47","slug":"o-que-e-metade-da-camada-de-valor-raios-x-definicao","status":"publish","type":"post","link":"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-metade-da-camada-de-valor-raios-x-definicao\/","title":{"rendered":"O que \u00e9 metade da camada de valor &#8211; Raios-X &#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\">A camada de metade do valor expressa a espessura do material absorvente necess\u00e1rio para reduzir a intensidade da radia\u00e7\u00e3o incidente por um fator de dois.\u00a0Camada de metade do valor &#8211; raios-X<\/div>\n<\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<p><strong>Os raios X<\/strong>\u00a0, tamb\u00e9m conhecidos como\u00a0<strong>radia\u00e7\u00e3o X<\/strong>\u00a0, referem-se \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de altas energias.\u00a0Os raios X s\u00e3o\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/\">f\u00f3tons de<\/a>\u00a0alta energia,\u00a0com comprimentos de onda curtos e, portanto, frequ\u00eancia muito alta.\u00a0A frequ\u00eancia de radia\u00e7\u00e3o \u00e9 o par\u00e2metro chave de todos os f\u00f3tons, porque determina a energia de um f\u00f3ton.\u00a0Os f\u00f3tons s\u00e3o classificados de acordo com as energias das ondas de r\u00e1dio de baixa energia e radia\u00e7\u00e3o infravermelha, atrav\u00e9s da luz vis\u00edvel, aos raios X de alta energia e raios\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/gamma-ray\/\">gama<\/a>\u00a0.<\/p>\n<p>A maioria dos raios X tem um comprimento de onda variando de 0,01 a 10 nan\u00f4metros (3 \u00d7 10\u00a0<sup>16<\/sup>\u00a0Hz a 3 \u00d7 10\u00a0<sup>19<\/sup>\u00a0Hz), correspondendo a energias na faixa de 100 eV a 100 keV.\u00a0Os comprimentos de onda dos raios X s\u00e3o mais curtos que os dos raios UV e geralmente mais longos que os dos raios gama.\u00a0A distin\u00e7\u00e3o entre raios X e raios gama n\u00e3o \u00e9 t\u00e3o simples e mudou nas \u00faltimas d\u00e9cadas.\u00a0De acordo com a defini\u00e7\u00e3o atualmente v\u00e1lida, os\u00a0<strong>raios X s\u00e3o emitidos por el\u00e9trons<\/strong>\u00a0fora do n\u00facleo, enquanto\u00a0<strong>os raios gama s\u00e3o emitidos pelo n\u00facleo<\/strong>\u00a0.<\/p>\n<h2>Camada de metade do valor<\/h2>\n<p><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/half-value-layers.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-12759 lazy-loaded\" src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/extrinsic-doped-semiconductor-p-type-acceptor-300x206.png\" alt=\"meia camada de valor\" width=\"291\" height=\"300\" data-lazy-type=\"image\" data-src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/extrinsic-doped-semiconductor-p-type-acceptor-300x206.png\" \/><\/a>A camada de metade do valor expressa a espessura do material absorvente necess\u00e1rio para reduzir a intensidade da radia\u00e7\u00e3o incidente por um\u00a0<strong>fator de dois<\/strong>\u00a0.\u00a0Existem duas caracter\u00edsticas principais da camada de meio valor:<\/p>\n<ul>\n<li>A\u00a0<b>camada de metade do valor<\/b>\u00a0diminui \u00e0 medida que o n\u00famero at\u00f4mico do absorvedor aumenta.\u00a0Por exemplo, s\u00e3o necess\u00e1rios 35 m de ar para reduzir a intensidade de um feixe de raios X de 100 keV por um fator de dois, enquanto apenas 0,12 mm de chumbo podem fazer a mesma coisa.<\/li>\n<li>A\u00a0<b>camada de metade do valor<\/b>\u00a0para todos os materiais aumenta com a energia dos raios-X.\u00a0Por exemplo, de 0,26 cm para ferro a 100 keV a cerca de 0,64 cm a 200 keV.<\/li>\n<\/ul>\n<h2>Camada de metade do valor &#8211; exemplo:<\/h2>\n<p>De quanto \u00e1gua \u00e9 necess\u00e1ria a escotilha, se voc\u00ea deseja reduzir a intensidade de um\u00a0feixe de raios X\u00a0<strong>monoenerg\u00e9tico de<\/strong>\u00a0100 keV\u00a0(\u00a0<strong>feixe estreito<\/strong>\u00a0) para\u00a0<strong>1%<\/strong>\u00a0de sua intensidade incidente?\u00a0A camada de meio valor para raios-X de 100 keV na \u00e1gua \u00e9 de 4,15 cm e o coeficiente de atenua\u00e7\u00e3o linear para raios-X de 100 keV na \u00e1gua \u00e9 de 0,167 cm-\u00a0<sup>1<\/sup>\u00a0.\u00a0O problema \u00e9 bastante simples e pode ser descrito pela seguinte equa\u00e7\u00e3o:<\/p>\n<p><a href=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/x-ray-attenuation-equation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25213 lazy-loaded\" src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/x-ray-attenuation-equation.png\" alt=\"\" width=\"116\" height=\"62\" data-lazy-type=\"image\" data-src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/x-ray-attenuation-equation.png\" \/><\/a>Se a camada de meio valor para a \u00e1gua for 4,15 cm, o coeficiente de atenua\u00e7\u00e3o linear \u00e9:<a href=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/linear-attenuation-example.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25212 lazy-loaded\" src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/linear-attenuation-example.png\" alt=\"\" width=\"196\" height=\"63\" data-lazy-type=\"image\" data-src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/linear-attenuation-example.png\" \/><\/a>Agora podemos usar a equa\u00e7\u00e3o de atenua\u00e7\u00e3o exponencial:<a href=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/x-ray-attenuation-problem-with-solution.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25211 lazy-loaded\" src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/x-ray-attenuation-problem-with-solution.png\" alt=\"atenua\u00e7\u00e3o de raios-x - problema com solu\u00e7\u00e3o\" width=\"238\" height=\"225\" data-lazy-type=\"image\" data-src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/x-ray-attenuation-problem-with-solution.png\" \/><\/a><\/p>\n<p>Portanto, a espessura necess\u00e1ria da \u00e1gua \u00e9 de cerca de\u00a0<strong>27,58 cm<\/strong>\u00a0.\u00a0Essa espessura \u00e9 relativamente grande e \u00e9 causada por um pequeno n\u00famero at\u00f4mico de hidrog\u00eanio e oxig\u00eanio.\u00a0Se calcularmos o mesmo problema para o\u00a0<strong>chumbo (Pb)<\/strong>\u00a0, obteremos a espessura\u00a0<strong>x = 0,077 cm<\/strong>\u00a0.<\/p>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<p><strong><span>Camadas de metade do valor<\/span><\/strong><\/p>\n<p><strong><span>Tabela de camadas de meio valor<\/span><\/strong><span>\u00a0(em cm) para diferentes materiais com energias de f\u00f3tons 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>3555 cm<\/span><\/td>\n<td><span>4359 cm<\/span><\/td>\n<td><span>6189 cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>\u00c1gua<\/span><\/td>\n<td><span>4,15 cm<\/span><\/td>\n<td><span>5.1 cm<\/span><\/td>\n<td><span>7.15 cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Carbono<\/span><\/td>\n<td><span>2,07 cm<\/span><\/td>\n<td><span>2,53 cm<\/span><\/td>\n<td><span>3.54 cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Alum\u00ednio<\/span><\/td>\n<td><span>1,59 cm<\/span><\/td>\n<td><span>2,14 cm<\/span><\/td>\n<td><span>3.05 cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Ferro<\/span><\/td>\n<td><span>0,26 cm<\/span><\/td>\n<td><span>0,64 cm<\/span><\/td>\n<td><span>1.06 cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Cobre<\/span><\/td>\n<td><span>0,18 cm<\/span><\/td>\n<td><span>0,53 cm<\/span><\/td>\n<td><span>0,95 cm<\/span><\/td>\n<\/tr>\n<tr>\n<td><span>Conduzir<\/span><\/td>\n<td><span>\u00a00.012 cm<\/span><\/td>\n<td><span>\u00a00.068 cm<\/span><\/td>\n<td><span>\u00a00,42 cm<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<div class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights  lgc-first lgc-last\">\n<div class=\"inside-grid-column\">\n<div class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-arrow\" data-anchor=\"References\">\n<div class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\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 camada de metade do valor expressa a espessura do material absorvente necess\u00e1rio para reduzir a intensidade da radia\u00e7\u00e3o incidente por um fator de dois.\u00a0Camada de metade do valor &#8211; raios-X Os raios X\u00a0, tamb\u00e9m conhecidos como\u00a0radia\u00e7\u00e3o X\u00a0, referem-se \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de altas energias.\u00a0Os raios X s\u00e3o\u00a0f\u00f3tons de\u00a0alta &#8230; <a title=\"O que \u00e9 metade da camada de valor &#8211; Raios-X &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-metade-da-camada-de-valor-raios-x-definicao\/\" aria-label=\"More on O que \u00e9 metade da camada de valor &#8211; Raios-X &#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 metade da camada de valor - Raios-X - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"A camada de metade do valor expressa a espessura do material absorvente necess\u00e1rio para reduzir a intensidade da radia\u00e7\u00e3o incidente por um fator de dois. 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