{"id":18254,"date":"2020-06-27T15:57:07","date_gmt":"2020-06-27T15:57:07","guid":{"rendered":"https:\/\/www.radiation-dosimetry.org\/o-que-e-atenuacao-de-raios-gama-definicao\/"},"modified":"2020-07-24T10:34:45","modified_gmt":"2020-07-24T10:34:45","slug":"o-que-e-atenuacao-de-raios-gama-definicao","status":"publish","type":"post","link":"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-atenuacao-de-raios-gama-definicao\/","title":{"rendered":"O que \u00e9 atenua\u00e7\u00e3o de raios gama &#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 atenua\u00e7\u00e3o dos raios gama descreve a atenua\u00e7\u00e3o dos raios gama monoenerg\u00e9ticos colimados em um feixe estreito e sua passagem pelo material.\u00a0Dosimetria de Radia\u00e7\u00e3o<\/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<h2>Atenua\u00e7\u00e3o de raios gama<\/h2>\n<p>Veja tamb\u00e9m:\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/x-rays-roentgen-radiation\/x-ray-attenuation\/\">Atenua\u00e7\u00e3o de raios-X<\/a><\/p>\n<p>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<strong>\u03c3 = \u03c3\u00a0<sub>f<\/sub>\u00a0+ \u03c3\u00a0<sub>C<\/sub>\u00a0+ \u03c3\u00a0<sub>p\u00a0<\/sub><\/strong><\/p>\n<ul>\n<li><strong>\u03c3\u00a0<sub>f<\/sub>\u00a0&#8211; Efeito fotoel\u00e9trico<\/strong><\/li>\n<\/ul>\n<ul>\n<li><strong>\u03c3\u00a0<sub>C<\/sub>\u00a0&#8211; espalhamento de Compton<\/strong><\/li>\n<\/ul>\n<ul>\n<li><strong>\u03c3\u00a0<sub>p<\/sub>\u00a0&#8211; Produ\u00e7\u00e3o em pares<\/strong><\/li>\n<\/ul>\n<p>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<strong>efeito fotoel\u00e9trico<\/strong>\u00a0domina.\u00a0<strong>A dispers\u00e3o de Compton<\/strong>\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<strong>a produ\u00e7\u00e3o de pares el\u00e9tron-p\u00f3sitron<\/strong>\u00a0domina a altas energias. Com base na defini\u00e7\u00e3o da se\u00e7\u00e3o transversal da intera\u00e7\u00e3o, pode-se derivar a depend\u00eancia da intensidade dos raios gama na espessura do material absorvente.\u00a0Se\u00a0<strong>raios gama monoenerg\u00e9ticos<\/strong>\u00a0s\u00e3o colimados em um\u00a0<strong>feixe estreito<\/strong>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 deve ser uma\u00a0<strong>atenua\u00e7\u00e3o exponencial<\/strong>\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<strong>coeficiente de atenua\u00e7\u00e3o linear<\/strong>\u00a0:<\/p>\n<p><strong>\u03bc = \u03c4\u00a0<sub>(fotoel\u00e9trico)<\/sub>\u00a0+ \u03c3\u00a0<sub>(Compton)<\/sub>\u00a0+ \u03ba\u00a0<sub>(par)<\/sub><\/strong><\/p>\n<figure id=\"attachment_11791\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11791\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/attenuation.png\"><img loading=\"lazy\" class=\"size-full wp-image-11796 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/attenuation.png\" alt=\"Atenua\u00e7\u00e3o de raios gama\" width=\"570\" height=\"357\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/attenuation.png\" \/><\/a><figcaption id=\"caption-attachment-11791\" class=\"wp-caption-text\">A import\u00e2ncia relativa de v\u00e1rios processos de intera\u00e7\u00e3o da radia\u00e7\u00e3o gama com a mat\u00e9ria.<\/figcaption><\/figure>\n<h2>Coeficiente de atenua\u00e7\u00e3o linear<\/h2>\n<p>A atenua\u00e7\u00e3o da radia\u00e7\u00e3o gama pode ser descrita pela seguinte equa\u00e7\u00e3o.<\/p>\n<p><strong>I = I\u00a0<sub>0<\/sub>\u00a0.e\u00a0<sup>-\u03bcx<\/sup><\/strong><\/p>\n<p>, onde I \u00e9 a intensidade ap\u00f3s a atenua\u00e7\u00e3o, I\u00a0<sub>o<\/sub>\u00a0\u00e9 a intensidade do incidente, \u03bc \u00e9 o coeficiente de atenua\u00e7\u00e3o linear (cm\u00a0<sup>-1<\/sup>\u00a0) e a espessura f\u00edsica do absorvedor (cm).<\/p>\n<figure id=\"attachment_11792\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11792\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/exponential-attenuation.png\"><img loading=\"lazy\" class=\"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><figcaption id=\"caption-attachment-11792\" class=\"wp-caption-text\">Depend\u00eancia da intensidade da radia\u00e7\u00e3o gama na espessura do absorvedor<\/figcaption><\/figure>\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><span>Camada de metade do valor<\/span><\/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><span>A camada de meio valor expressa a espessura do material absorvente necess\u00e1rio para reduzir a intensidade da radia\u00e7\u00e3o incidente por um\u00a0<\/span><strong><span>fator de dois<\/span><\/strong><span>\u00a0.\u00a0Existem duas caracter\u00edsticas principais da camada de meio valor:<\/span><\/p>\n<ul>\n<li><span>A\u00a0<\/span><b><span>camada de metade do valor<\/span><\/b><span>\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 gama de 100 keV por um fator de dois, enquanto apenas 0,12 mm de chumbo podem fazer a mesma coisa.<\/span><\/li>\n<li><span>A\u00a0<\/span><b><span>camada de metade do valor<\/span><\/b><span>\u00a0para todos os materiais aumenta com a energia dos raios gama.\u00a0Por exemplo, de 0,26 cm para ferro a 100 keV a cerca de 1,06 cm a 500 keV.<\/span><\/li>\n<\/ul>\n<h2><span>Coeficiente de atenua\u00e7\u00e3o de massa<\/span><\/h2>\n<p><span>Ao caracterizar um material absorvente, \u00e0s vezes podemos usar o coeficiente de atenua\u00e7\u00e3o da massa. \u00a0<\/span><strong><span>O coeficiente de atenua\u00e7\u00e3o da massa<\/span><\/strong><span>\u00a0\u00e9 definido como a raz\u00e3o entre o coeficiente de atenua\u00e7\u00e3o linear e a densidade do absorvedor\u00a0<\/span><strong><span>(\u03bc \/ \u03c1)<\/span><\/strong><span>\u00a0.\u00a0A 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>&#8211; (\u03bc \/ \u03c1) .\u03c1l<\/span><\/sup><\/strong><\/p>\n<p><span>, onde \u03c1 \u00e9 a densidade do material, (\u03bc \/ \u03c1) \u00e9 o coeficiente de atenua\u00e7\u00e3o da massa e \u03c1.l \u00e9 a espessura da massa.\u00a0A unidade de medida usada para o coeficiente de atenua\u00e7\u00e3o de massa cm\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0g\u00a0<\/span><sup><span>-1<\/span><\/sup><span>\u00a0.Para energias intermedi\u00e1rias, a dispers\u00e3o de Compton domina e diferentes absorvedores t\u00eam coeficientes de atenua\u00e7\u00e3o de massa aproximadamente iguais.\u00a0Isso se deve ao fato de que a se\u00e7\u00e3o transversal da dispers\u00e3o de Compton \u00e9 proporcional ao Z (n\u00famero at\u00f4mico) e, portanto, o coeficiente \u00e9 proporcional \u00e0 densidade do material \u03c1.\u00a0Em valores pequenos de energia de raios gama ou em valores altos de energia de raios gama, em que o coeficiente \u00e9 proporcional a pot\u00eancias mais altas do n\u00famero at\u00f4mico Z (para efeito fotoel\u00e9trico \u03c3\u00a0<\/span><sub><span>f<\/span><\/sub><span>\u00a0~ Z\u00a0<\/span><sup><span>5<\/span><\/sup><span>\u00a0; para produ\u00e7\u00e3o de pares \u03c3\u00a0<\/span><sub><span>p<\/span><\/sub><span>\u00a0~ Z<\/span><sup><span>2<\/span><\/sup><span>\u00a0), o coeficiente de atenua\u00e7\u00e3o \u03bc n\u00e3o \u00e9 constante.<\/span><\/p>\n<h2><span>Exemplo:<\/span><\/h2>\n<p><span>De quanto \u00e1gua voc\u00ea precisa, se voc\u00ea deseja reduzir a intensidade de um\u00a0feixe de raios gama\u00a0<\/span><strong><span>monoenerg\u00e9tico de<\/span><\/strong><span>\u00a0500 keV\u00a0(\u00a0<\/span><strong><span>feixe estreito<\/span><\/strong><span>\u00a0) para\u00a0<\/span><strong><span>1%<\/span><\/strong><span>\u00a0de sua intensidade incidente?\u00a0A camada de meio valor para raios gama de 500 keV na \u00e1gua \u00e9 de 7,15 cm e o coeficiente de atenua\u00e7\u00e3o linear para raios gama de 500 keV na \u00e1gua \u00e9 de 0,097 cm\u00a0<\/span><sup><span>-1<\/span><\/sup><span>\u00a0.\u00a0<\/span><span>A quest\u00e3o \u00e9 bastante simples e pode ser descrita pela seguinte equa\u00e7\u00e3o:<\/span><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=I(x)%3D%5Cfrac%7BI_%7B0%7D%7D%7B100%7D%2C%5C%3B%5C%3B%20when%5C%3B%20x%20%3D%3F%20\" alt=\"I (x) = frac {I_ {0}} {100}, ;;  quando;  x =?\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=I(x)%3D%5Cfrac%7BI_%7B0%7D%7D%7B100%7D%2C%5C%3B%5C%3B%20when%5C%3B%20x%20%3D%3F%20\" \/><span>Se a camada de meio valor para a \u00e1gua for 7,15 cm, o coeficiente de atenua\u00e7\u00e3o linear \u00e9:<\/span><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Cmu%3D%5Cfrac%7Bln2%7D%7B7.15%7D%3D0.097cm%5E%7B-1%7D\" alt=\"mu = frac {ln2} {7,15} = 0,097cm ^ {- 1}\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Cmu%3D%5Cfrac%7Bln2%7D%7B7.15%7D%3D0.097cm%5E%7B-1%7D\" \/><span>Agora podemos usar a equa\u00e7\u00e3o de atenua\u00e7\u00e3o exponencial:<\/span><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=I(x)%3DI_0%5C%3Bexp%5C%3B(-%5Cmu%20x)\" alt=\"I (x) = I_0; exp; (- mu x)\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=I(x)%3DI_0%5C%3Bexp%5C%3B(-%5Cmu%20x)\" \/><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Cfrac%7BI_0%7D%7B100%7D%3DI_0%5C%3Bexp%5C%3B(-0.097%20x)\" alt=\"frac {I_0} {100} = I_0; exp; (- 0,097 x)\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Cfrac%7BI_0%7D%7B100%7D%3DI_0%5C%3Bexp%5C%3B(-0.097%20x)\" \/><span>Portanto<\/span><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Cfrac%7B1%7D%7B100%7D%3D%5C%3Bexp%5C%3B(-0.097%20x)\" alt=\"frac {1} {100} =; exp; (- 0,097 x)\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Cfrac%7B1%7D%7B100%7D%3D%5C%3Bexp%5C%3B(-0.097%20x)\" \/><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=ln%5Cfrac%7B1%7D%7B100%7D%3D-ln%5C%3B100%3D-0.097%20x\" alt=\"lnfrac {1} {100} = - ln; 100 = -0,097 x\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=ln%5Cfrac%7B1%7D%7B100%7D%3D-ln%5C%3B100%3D-0.097%20x\" \/><img class=\"mathtex-equation-editor aligncenter lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=x%3D%5Cfrac%7Bln100%7D%7B%7B0.097%7D%7D%3D47.47%5C%3Bcm\" alt=\"x = frac {ln100} {{0,097}} = 47,47; cm\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=x%3D%5Cfrac%7Bln100%7D%7B%7B0.097%7D%7D%3D47.47%5C%3Bcm\" \/><span>Portanto, a espessura necess\u00e1ria da \u00e1gua \u00e9 de cerca de\u00a0<\/span><strong><span>47,5 cm<\/span><\/strong><span>\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<\/span><strong><span>chumbo (Pb)<\/span><\/strong><span>\u00a0, obteremos a espessura\u00a0<\/span><strong><span>x = 2,8 cm<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><span>Coeficientes de atenua\u00e7\u00e3o linear<\/span><\/p>\n<p><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<p><span id=\"more-32\"><\/span><span>Camadas de metade do valor<\/span><\/p>\n<p><strong><span>Tabela de camadas de meio valor<\/span><\/strong><span>\u00a0(em cm) 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>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<h2><span>Validade da lei exponencial<\/span><\/h2>\n<p><span>A lei exponencial sempre descrever\u00e1 a atenua\u00e7\u00e3o da radia\u00e7\u00e3o prim\u00e1ria pela mat\u00e9ria.\u00a0Se part\u00edculas secund\u00e1rias forem produzidas ou se a radia\u00e7\u00e3o prim\u00e1ria mudar sua energia ou dire\u00e7\u00e3o, a atenua\u00e7\u00e3o efetiva ser\u00e1 muito menor.\u00a0A radia\u00e7\u00e3o penetrar\u00e1 mais profundamente na mat\u00e9ria do que a prevista pela lei exponencial.\u00a0O processo deve ser levado em considera\u00e7\u00e3o ao avaliar o efeito da prote\u00e7\u00e3o contra radia\u00e7\u00e3o.<\/span><\/p>\n<figure id=\"attachment_11803\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11803\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/secondary_length.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11808 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/secondary_length-300x165.png\" alt=\"Exemplo de acumula\u00e7\u00e3o de part\u00edculas secund\u00e1rias.  Depende fortemente do car\u00e1ter e dos par\u00e2metros das part\u00edculas prim\u00e1rias.\" width=\"300\" height=\"165\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/secondary_length-300x165.png\" \/><\/a><figcaption id=\"caption-attachment-11803\" class=\"wp-caption-text\"><span>Exemplo de acumula\u00e7\u00e3o de part\u00edculas secund\u00e1rias.\u00a0Depende fortemente do car\u00e1ter e dos par\u00e2metros das part\u00edculas prim\u00e1rias.<\/span><\/figcaption><\/figure>\n<h2><span>Fatores de ac\u00famulo para blindagem de raios gama<\/span><\/h2>\n<p><span>O\u00a0<\/span><strong><span>fator de acumula\u00e7\u00e3o<\/span><\/strong><span>\u00a0\u00e9 um fator de corre\u00e7\u00e3o que considera a influ\u00eancia da radia\u00e7\u00e3o dispersa mais quaisquer\u00a0<\/span><strong><span>part\u00edculas secund\u00e1rias<\/span><\/strong><span>\u00a0no meio durante os c\u00e1lculos de blindagem.\u00a0Se queremos dar conta do ac\u00famulo de radia\u00e7\u00e3o secund\u00e1ria, precisamos incluir o\u00a0<\/span><strong><span>fator de ac\u00famulo<\/span><\/strong><span>\u00a0.\u00a0O fator de acumula\u00e7\u00e3o \u00e9 ent\u00e3o um fator multiplicativo que responde pela resposta aos f\u00f3tons n\u00e3o colididos, de modo a incluir a contribui\u00e7\u00e3o dos f\u00f3tons dispersos.\u00a0Assim, o fator de acumula\u00e7\u00e3o pode ser obtido como uma raz\u00e3o entre a dose total e a resposta para a dose n\u00e3o coletada.<\/span><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/shielding-of-ionizing-radiation\/shielding-gamma-radiation\/\"><span>Prote\u00e7\u00e3o de raios gama<\/span><\/a><\/p>\n<p><span>A\u00a0<\/span><strong><span>f\u00f3rmula estendida<\/span><\/strong><span>\u00a0para o c\u00e1lculo da taxa de dose \u00e9:<\/span><\/p>\n<p><a href=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Buildup-Factor-in-Dose-Rate-Calculation.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-25983 lazy-loaded\" src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Buildup-Factor-in-Dose-Rate-Calculation.png\" alt=\"Fator de Ac\u00famulo\" width=\"689\" height=\"348\" data-lazy-type=\"image\" data-src=\"http:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Buildup-Factor-in-Dose-Rate-Calculation.png\" \/><\/a><\/p>\n<p><span>O padr\u00e3o ANSI \/ ANS-6.4.3-1991 de coeficientes de atenua\u00e7\u00e3o de raios gama e fatores de ac\u00famulo para materiais de engenharia cont\u00e9m coeficientes de atenua\u00e7\u00e3o de raios gama derivados e fatores de ac\u00famulo para materiais e elementos de engenharia selecionados para uso em c\u00e1lculos de blindagem (ANSI \/ ANS-6.1 .1, 1991).<\/span><\/p>\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 atenua\u00e7\u00e3o dos raios gama descreve a atenua\u00e7\u00e3o dos raios gama monoenerg\u00e9ticos colimados em um feixe estreito e sua passagem pelo material.\u00a0Dosimetria de Radia\u00e7\u00e3o Atenua\u00e7\u00e3o de raios gama Veja tamb\u00e9m:\u00a0Atenua\u00e7\u00e3o de raios-X 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+ &#8230; <a title=\"O que \u00e9 atenua\u00e7\u00e3o de raios gama &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-atenuacao-de-raios-gama-definicao\/\" aria-label=\"More on O que \u00e9 atenua\u00e7\u00e3o de raios gama &#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 atenua\u00e7\u00e3o de raios gama - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"A atenua\u00e7\u00e3o dos raios gama descreve a atenua\u00e7\u00e3o dos raios gama monoenerg\u00e9ticos colimados em um feixe estreito e sua passagem pelo material. 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