{"id":17405,"date":"2020-06-13T02:09:44","date_gmt":"2020-06-13T02:09:44","guid":{"rendered":"https:\/\/www.radiation-dosimetry.org\/o-que-e-interacao-de-neutrons-com-materia-definicao\/"},"modified":"2020-07-20T10:42:44","modified_gmt":"2020-07-20T10:42:44","slug":"o-que-e-interacao-de-neutrons-com-materia-definicao","status":"publish","type":"post","link":"http:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-interacao-de-neutrons-com-materia-definicao\/","title":{"rendered":"O que \u00e9 intera\u00e7\u00e3o de n\u00eautrons com mat\u00e9ria &#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\">N\u00eautrons podem interagir com a mat\u00e9ria de v\u00e1rias maneiras.\u00a0N\u00eautrons s\u00e3o part\u00edculas neutras, portanto colidem com n\u00facleos, n\u00e3o com \u00e1tomos.\u00a0Intera\u00e7\u00f5es de n\u00eautrons com mat\u00e9ria.\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>Intera\u00e7\u00f5es de n\u00eautrons com mat\u00e9ria<\/h2>\n<p><strong>Os n\u00eautrons<\/strong>\u00a0s\u00e3o part\u00edculas neutras; portanto, eles viajam em\u00a0<strong>linhas retas<\/strong>\u00a0, desviando-se do caminho apenas quando colidem com um n\u00facleo para serem dispersos em uma nova dire\u00e7\u00e3o ou absorvidos.\u00a0Nem os el\u00e9trons que cercam (nuvem de el\u00e9trons at\u00f4micas) um n\u00facleo nem o campo el\u00e9trico causado por um n\u00facleo carregado positivamente afetam o v\u00f4o de um n\u00eautron.\u00a0Em resumo, os\u00a0<strong>n\u00eautrons colidem com n\u00facleos<\/strong>\u00a0, n\u00e3o com \u00e1tomos.\u00a0Uma caracter\u00edstica muito descritiva da transmiss\u00e3o de n\u00eautrons atrav\u00e9s da mat\u00e9ria a granel \u00e9 o comprimento m\u00e9dio do caminho livre (\u00a0<strong><b>\u03bb &#8211; lambda<\/b><\/strong>\u00a0), que \u00e9 a dist\u00e2ncia m\u00e9dia que um n\u00eautron viaja entre intera\u00e7\u00f5es.\u00a0Pode ser calculado a partir da seguinte equa\u00e7\u00e3o:<\/p>\n<p><strong><b>\u03bb = 1 \/ \u03a3<\/b><\/strong><\/p>\n<p><strong>Os n\u00eautrons podem interagir com os n\u00facleos de uma das seguintes maneiras:<\/strong><\/p>\n<p><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/neutron-nucleus-reactions.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-12490 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/neutron-nucleus-reactions.png\" alt=\"N\u00eautron - Rea\u00e7\u00f5es Nucleares\" width=\"960\" height=\"720\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/neutron-nucleus-reactions.png\" \/><\/a><\/p>\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=\"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><span>Tipos de rea\u00e7\u00f5es nucleares de n\u00eautrons<\/span><\/h2>\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-accordion su-u-trim\">\n<div class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\">\n<ul>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span>Rea\u00e7\u00e3o de dispers\u00e3o el\u00e1stica<\/span><\/li>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">Rea\u00e7\u00e3o de dispers\u00e3o inel\u00e1stica<\/li>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">Absor\u00e7\u00e3o de N\u00eautrons<\/li>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">Captura radiativa<\/li>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">Fic\u00e3o nuclear<\/li>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">Emiss\u00e3o de n\u00eautrons<\/li>\n<li class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">Eje\u00e7\u00e3o de part\u00edculas carregadas<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<h2><span>Se\u00e7\u00e3o transversal de n\u00eautrons<\/span><\/h2>\n<figure id=\"attachment_371\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-371\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/capture_cross_section.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-371 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/capture_cross_section-300x213.jpg\" alt=\"Se\u00e7\u00e3o transversal de n\u00eautrons\" width=\"300\" height=\"213\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/capture_cross_section-300x213.jpg\" \/><\/a><figcaption id=\"caption-attachment-371\" class=\"wp-caption-text\"><span>Sec\u00e7\u00f5es t\u00edpicas do material de fiss\u00e3o.\u00a0Diminuir a velocidade dos n\u00eautrons resulta no aumento da probabilidade de intera\u00e7\u00e3o (por exemplo, rea\u00e7\u00e3o de fiss\u00e3o).<\/span><\/figcaption><\/figure>\n<p><span>A extens\u00e3o em que os n\u00eautrons interagem com os n\u00facleos \u00e9 descrita em termos de quantidades conhecidas como\u00a0<\/span><strong><span>se\u00e7\u00f5es transversais<\/span><\/strong><span>\u00a0.\u00a0<\/span><strong><span>As se\u00e7\u00f5es transversais<\/span><\/strong><span>\u00a0s\u00e3o usadas para expressar a\u00a0<\/span><strong><span>probabilidade<\/span><\/strong><span>\u00a0de intera\u00e7\u00e3o espec\u00edfica entre um\u00a0<\/span><strong><span>n\u00eautron incidente<\/span><\/strong><span>\u00a0e um\u00a0<\/span><strong><span>n\u00facleo alvo<\/span><\/strong><span>\u00a0.\u00a0Deve-se notar que essa probabilidade n\u00e3o depende das dimens\u00f5es reais do alvo.\u00a0Em conjunto com o fluxo de n\u00eautrons, permite o c\u00e1lculo da taxa de rea\u00e7\u00e3o, por exemplo, para derivar a energia t\u00e9rmica de uma usina nuclear.\u00a0A unidade padr\u00e3o para medir a se\u00e7\u00e3o microsc\u00f3pica (\u00a0<\/span><strong><span>\u03c3-sigma<\/span><\/strong><span>\u00a0) \u00e9 o\u00a0<\/span><strong><span>celeiro<\/span><\/strong><span>\u00a0, que \u00e9 igual a\u00a0<\/span><strong><span>10\u00a0<\/span><sup><span>-28<\/span><\/sup><span>\u00a0\u00a0m\u00a0<\/span><sup><span>2<\/span><\/sup><\/strong><span>.\u00a0Esta unidade \u00e9 muito pequena, portanto, celeiros (abreviados como &#8220;b&#8221;) s\u00e3o comumente usados.\u00a0A se\u00e7\u00e3o microsc\u00f3pica pode ser interpretada como a\u00a0&#8216;\u00e1rea-alvo&#8217;\u00a0<\/span><strong><span>eficaz em<\/span><\/strong><span>\u00a0que um n\u00facleo\u00a0<\/span><strong><span>interage<\/span><\/strong><span>\u00a0com um n\u00eautron incidente.<\/span><\/p>\n<p><span>Uma\u00a0<\/span><strong><span>se\u00e7\u00e3o macrosc\u00f3pica<\/span><\/strong><span>\u00a0\u00e9 derivada de microsc\u00f3pico e a densidade do material:<\/span><\/p>\n<p><strong>\u00a0<\/strong><strong><span>\u03a3 = \u03c3.N<\/span><\/strong><\/p>\n<p><strong>\u00a0<\/strong><span>Aqui \u03c3, que possui unidades de m\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0, \u00e9 chamado de se\u00e7\u00e3o microsc\u00f3pica.\u00a0Como as unidades de N (densidade dos n\u00facleos) s\u00e3o n\u00facleos \/ m\u00a0<\/span><sup><span>3<\/span><\/sup><span>\u00a0, a\u00a0<\/span><strong><span>se\u00e7\u00e3o macrosc\u00f3pica\u00a0<\/span><\/strong><strong><span>\u03a3<\/span><\/strong><span>\u00a0\u00a0possui unidades de\u00a0<\/span><strong><span>m\u00a0<\/span><sup><span>-1<\/span><\/sup><\/strong><span>\u00a0, portanto, de fato, \u00e9 um nome incorreto, porque n\u00e3o \u00e9 uma unidade correta de se\u00e7\u00f5es transversais.<\/span><\/p>\n<p><strong><span>As se\u00e7\u00f5es transversais de n\u00eautrons<\/span><\/strong><span>\u00a0constituem par\u00e2metros-chave do combust\u00edvel nuclear.\u00a0As se\u00e7\u00f5es transversais de n\u00eautrons devem ser calculadas para conjuntos de combust\u00edvel novo geralmente em modelos bidimensionais da treli\u00e7a de combust\u00edvel.<\/span><\/p>\n<p><strong>\u00a0<\/strong><span>A se\u00e7\u00e3o transversal de n\u00eautrons \u00e9 vari\u00e1vel e depende de:<\/span><\/p>\n<ul>\n<li><strong><span>N\u00facleo alvo<\/span><\/strong><span>\u00a0(hidrog\u00eanio, boro, ur\u00e2nio, etc.) Cada is\u00f3topo tem seu pr\u00f3prio conjunto de se\u00e7\u00f5es transversais.<\/span><\/li>\n<li><strong><span>Tipo de rea\u00e7\u00e3o<\/span><\/strong><span>\u00a0(captura, fiss\u00e3o, etc.).\u00a0As se\u00e7\u00f5es transversais s\u00e3o diferentes para cada rea\u00e7\u00e3o nuclear.<\/span><\/li>\n<li><strong><span>Energia de n\u00eautrons<\/span><\/strong><span>\u00a0(n\u00eautron t\u00e9rmico, n\u00eautron de resson\u00e2ncia, n\u00eautron r\u00e1pido).\u00a0Para um determinado alvo e tipo de rea\u00e7\u00e3o, a se\u00e7\u00e3o transversal depende fortemente da energia de n\u00eautrons.\u00a0No caso comum, a se\u00e7\u00e3o transversal \u00e9 geralmente muito maior em baixas energias do que em altas energias.\u00a0\u00c9 por isso que a maioria dos reatores nucleares usa um moderador de n\u00eautrons para reduzir a energia do n\u00eautron e, assim, aumentar a probabilidade de fiss\u00e3o, essencial para produzir energia e sustentar a rea\u00e7\u00e3o em cadeia.<\/span><\/li>\n<li><strong><span>Energia alvo<\/span><\/strong><span>\u00a0(temperatura do material alvo &#8211; amplia\u00e7\u00e3o do Doppler) Essa depend\u00eancia n\u00e3o \u00e9 t\u00e3o significativa, mas a energia alvo influencia fortemente a seguran\u00e7a inerente dos reatores nucleares devido a uma amplia\u00e7\u00e3o do Doppler das resson\u00e2ncias.<\/span><\/li>\n<\/ul>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a title=\"JANIS\" href=\"http:\/\/www.oecd-nea.org\/janis\/\"><span>JANIS (software de informa\u00e7\u00e3o nuclear baseado em Java)\u00a0<\/span><\/a><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a title=\"Se\u00e7\u00e3o transversal de n\u00eautrons\" href=\"https:\/\/www.nuclear-power.com\/neutron-cross-section\/\" target=\"_blank\" rel=\"noopener noreferrer\"><span>Se\u00e7\u00e3o transversal de n\u00eautrons<\/span><\/a><\/p>\n<h2><span>Lei 1 \/ v<\/span><\/h2>\n<figure id=\"attachment_12069\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-12069\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/1v-Law.png\"><img loading=\"lazy\" class=\"size-medium wp-image-12069 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/radiation_protection_principles-300x233.gif\" alt=\"1 \/ v Direito\" width=\"300\" height=\"221\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/radiation_protection_principles-300x233.gif\" \/><\/a><figcaption id=\"caption-attachment-12069\" class=\"wp-caption-text\"><span>Para n\u00eautrons t\u00e9rmicos (na regi\u00e3o 1 \/ v), as se\u00e7\u00f5es transversais de absor\u00e7\u00e3o aumentam \u00e0 medida que a velocidade (energia cin\u00e9tica) do n\u00eautron diminui.<\/span><br \/>\n<span>Fonte: JANIS 4.0<\/span><\/figcaption><\/figure>\n<p><span>Para n\u00eautrons t\u00e9rmicos (\u00a0<\/span><strong><span>na regi\u00e3o 1 \/ v<\/span><\/strong><span>\u00a0), as se\u00e7\u00f5es transversais de absor\u00e7\u00e3o aumentam \u00e0 medida que a velocidade (energia cin\u00e9tica) do n\u00eautron diminui.\u00a0Portanto, a\u00a0<\/span><strong><span>lei 1 \/ v<\/span><\/strong><span>\u00a0pode ser usada para determinar a mudan\u00e7a na se\u00e7\u00e3o transversal de absor\u00e7\u00e3o, se o n\u00eautron estiver em equil\u00edbrio com um meio circundante.\u00a0Esse fen\u00f4meno se deve ao fato de a for\u00e7a nuclear entre o n\u00facleo alvo e o n\u00eautron ter mais tempo para interagir.<\/span><\/p>\n<p><img class=\"mathtex-equation-editor alignleft lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Csigma_a%20%5Csim%20%5Cfrac%7B1%7D%7Bv%7D%7D%7D%20%5Csim%20%5Cfrac%7B1%7D%7B%5Csqrt%7BE%7D%7D%7D%7D%7D%20%5Csim%20%5Cfrac%7B1%7D%7B%5Csqrt%7BT%7D%7D%7D%7D%7D\" alt=\"sigma_a sim frac {1} {v}}} sim frac {1} {sqrt {E}}}}} sim frac {1} {sqrt {T}}}}}\" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Csigma_a%20%5Csim%20%5Cfrac%7B1%7D%7Bv%7D%7D%7D%20%5Csim%20%5Cfrac%7B1%7D%7B%5Csqrt%7BE%7D%7D%7D%7D%7D%20%5Csim%20%5Cfrac%7B1%7D%7B%5Csqrt%7BT%7D%7D%7D%7D%7D\" \/><\/p>\n<p><span>Esta lei \u00e9 aplic\u00e1vel apenas para a se\u00e7\u00e3o transversal de absor\u00e7\u00e3o e somente na regi\u00e3o 1 \/ v.<\/span><\/p>\n<p><strong><span>Exemplo de se\u00e7\u00f5es transversais na regi\u00e3o 1 \/ v:<\/span><\/strong><\/p>\n<p><span>A se\u00e7\u00e3o transversal de absor\u00e7\u00e3o para 238U a 20 \u00b0 C = 293K (~ 0,0253 eV) \u00e9:<\/span><\/p>\n<p><img class=\"mathtex-equation-editor lazy-loaded\" src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Csigma_a(293K)%20%3D%202.68b%20\" alt=\"sigma_a (293K) = 2,68b \" align=\"absmiddle\" data-lazy-type=\"image\" data-src=\"http:\/\/chart.apis.google.com\/chart?cht=tx&amp;chl=%5Csigma_a(293K)%20%3D%202.68b%20\" \/><span>.<\/span><\/p>\n<p><span>A se\u00e7\u00e3o transversal de absor\u00e7\u00e3o para 238U a 1000 \u00b0 C = 1273K \u00e9 igual a:<\/span><\/p>\n<p><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Neutron-Cross-section-1-v-law.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-18571 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Neutron-Cross-section-1-v-law.png\" alt=\"Se\u00e7\u00e3o transversal de n\u00eautrons - lei 1-v\" width=\"462\" height=\"83\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Neutron-Cross-section-1-v-law.png\" \/><\/a><\/p>\n<p><span>Essa redu\u00e7\u00e3o da se\u00e7\u00e3o transversal \u00e9 causada apenas devido \u00e0 mudan\u00e7a de temperatura do meio circundante.<\/span><\/p>\n<h2><span>Captura de resson\u00e2ncia de n\u00eautrons<\/span><\/h2>\n<figure id=\"attachment_376\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-376\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Resonance_area.png\"><img loading=\"lazy\" class=\"size-medium wp-image-376 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Resonance_area-300x210.png\" alt=\"Picos de resson\u00e2ncia para captura radiativa de U238.\" width=\"300\" height=\"210\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Resonance_area-300x210.png\" \/><\/a><figcaption id=\"caption-attachment-376\" class=\"wp-caption-text\"><span>Picos de resson\u00e2ncia para captura radiativa de U238.\u00a0Nas energias de resson\u00e2ncia, a probabilidade de captura pode ser mais de 100x maior que o valor base.<\/span><br \/>\n<span>Fonte: Programa JANIS<\/span><\/figcaption><\/figure>\n<p><span>A se\u00e7\u00e3o transversal de absor\u00e7\u00e3o geralmente \u00e9 altamente dependente da energia de n\u00eautrons.\u00a0Observe que a fiss\u00e3o nuclear produz n\u00eautrons com uma energia m\u00e9dia de 2 MeV (200 TJ \/ kg, ou seja, 20.000 km \/ s).\u00a0O n\u00eautron pode ser dividido em tr\u00eas faixas de energia:<\/span><\/p>\n<ul>\n<li><span>N\u00eautron r\u00e1pido.\u00a0(10MeV &#8211; 1keV)<\/span><\/li>\n<li><span>N\u00eautron de resson\u00e2ncia (1keV &#8211; 1eV)<\/span><\/li>\n<li><span>N\u00eautron t\u00e9rmico.\u00a0(1eV &#8211; 0,025eV)<\/span><\/li>\n<\/ul>\n<p><span>Os n\u00eautrons de resson\u00e2ncia s\u00e3o chamados de resson\u00e2ncia por seu comportamento especial.\u00a0Nas energias de resson\u00e2ncia, a se\u00e7\u00e3o transversal pode atingir picos mais de 100x mais altos que o valor base da se\u00e7\u00e3o transversal.\u00a0Com essas energias, a captura de n\u00eautrons excede significativamente a probabilidade de fiss\u00e3o.\u00a0Portanto, \u00e9 muito importante (para reatores t\u00e9rmicos)\u00a0<strong>superar\u00a0<\/strong><\/span><strong><span>rapidamente<\/span><\/strong>\u00a0<span>essa faixa de energia e operar o reator com n\u00eautrons t\u00e9rmicos, resultando no aumento da probabilidade de fiss\u00e3o.<\/span><\/p>\n<h2><span>Alargamento Doppler<\/span><\/h2>\n<p><strong>\u00a0<\/strong><\/p>\n<figure id=\"attachment_378\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-378\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Doppler_broadening.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-378 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Doppler_broadening-300x161.jpg\" alt=\"efeito Doppler\" width=\"300\" height=\"161\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Doppler_broadening-300x161.jpg\" \/><\/a><figcaption id=\"caption-attachment-378\" class=\"wp-caption-text\"><span>O efeito Doppler melhora a estabilidade do reator.\u00a0A resson\u00e2ncia ampliada (aquecimento de um combust\u00edvel) resulta em uma maior probabilidade de absor\u00e7\u00e3o, causando inser\u00e7\u00e3o de reatividade negativa (redu\u00e7\u00e3o da pot\u00eancia do reator).<\/span><\/figcaption><\/figure>\n<p><span>Um\u00a0<\/span><strong><span>alargamento<\/span><\/strong><span>\u00a0de\u00a0<strong>Doppler<\/strong>\u00a0de resson\u00e2ncias \u00e9 um fen\u00f4meno importante, o que\u00a0<\/span><strong><span>melhora a estabilidade do reator<\/span><\/strong><span>\u00a0.\u00a0O coeficiente de temperatura imediata da maioria dos reatores t\u00e9rmicos \u00e9\u00a0<\/span><strong><span>negativo<\/span><\/strong><span>\u00a0, devido ao efeito Doppler nuclear.\u00a0Embora a se\u00e7\u00e3o transversal de absor\u00e7\u00e3o dependa significativamente da energia incidente de n\u00eautrons, o formato da curva da se\u00e7\u00e3o transversal tamb\u00e9m depende da temperatura alvo.<\/span><\/p>\n<p><span>Os n\u00facleos est\u00e3o localizados em \u00e1tomos que est\u00e3o em\u00a0<\/span><strong><span>movimento<\/span><\/strong><span>\u00a0cont\u00ednuo\u00a0devido \u00e0 sua energia t\u00e9rmica.\u00a0Como resultado desses\u00a0<\/span><strong><span>movimentos t\u00e9rmicos, os<\/span><\/strong><span>\u00a0n\u00eautrons que atingem um alvo parecem ter n\u00facleos no alvo uma propaga\u00e7\u00e3o cont\u00ednua de energia.\u00a0Isso, por sua vez, afeta a forma observada de resson\u00e2ncia.\u00a0A resson\u00e2ncia se torna\u00a0<\/span><strong><span>mais curta e mais larga do<\/span><\/strong><span>\u00a0que quando os n\u00facleos est\u00e3o em repouso.<\/span><\/p>\n<p><span>Embora a forma de uma resson\u00e2ncia mude com a temperatura, a\u00a0<\/span><strong><span>\u00e1rea total<\/span><\/strong><span>\u00a0sob a resson\u00e2ncia permanece essencialmente constante.\u00a0Mas isso\u00a0<\/span><strong><span>n\u00e3o implica\u00a0<\/span><\/strong><strong><span>absor\u00e7\u00e3o constante de n\u00eautrons<\/span><\/strong><span>\u00a0.\u00a0Apesar da \u00e1rea constante sob resson\u00e2ncia,\u00a0<\/span><strong><span>uma integral de resson\u00e2ncia<\/span><\/strong><span>\u00a0, que determina a absor\u00e7\u00e3o, aumenta com o aumento da temperatura alvo.\u00a0Obviamente, isso diminui o coeficiente k (a reatividade negativa \u00e9 inserida).<\/span><\/p>\n<h2><strong><span>Sec\u00e7\u00f5es transversais t\u00edpicas de materiais no reator<\/span><\/strong><\/h2>\n<p><span>A tabela a seguir mostra\u00a0<\/span><strong><span>se\u00e7\u00f5es transversais de n\u00eautrons<\/span><\/strong><span>\u00a0dos is\u00f3topos mais comuns do n\u00facleo do reator.<\/span><\/p>\n<figure id=\"attachment_381\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-381\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/cross-sections_nuclides.png\"><img loading=\"lazy\" class=\"size-full wp-image-381 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/cross-sections_nuclides.png\" alt=\"Tabela de se\u00e7\u00f5es transversais\" width=\"732\" height=\"441\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/cross-sections_nuclides.png\" \/><\/a><figcaption id=\"caption-attachment-381\" class=\"wp-caption-text\"><span>Tabela de se\u00e7\u00f5es transversais<\/span><\/figcaption><\/figure>\n<\/div>\n<\/div>\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-accordion su-u-trim\">\n<div class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\">\n<div class=\"su-spoiler-content su-u-clearfix su-u-trim\"><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\">\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<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>N\u00eautrons podem interagir com a mat\u00e9ria de v\u00e1rias maneiras.\u00a0N\u00eautrons s\u00e3o part\u00edculas neutras, portanto colidem com n\u00facleos, n\u00e3o com \u00e1tomos.\u00a0Intera\u00e7\u00f5es de n\u00eautrons com mat\u00e9ria.\u00a0Dosimetria de Radia\u00e7\u00e3o Intera\u00e7\u00f5es de n\u00eautrons com mat\u00e9ria Os n\u00eautrons\u00a0s\u00e3o part\u00edculas neutras; portanto, eles viajam em\u00a0linhas retas\u00a0, desviando-se do caminho apenas quando colidem com um n\u00facleo para serem dispersos em uma nova dire\u00e7\u00e3o &#8230; <a title=\"O que \u00e9 intera\u00e7\u00e3o de n\u00eautrons com mat\u00e9ria &#8211; defini\u00e7\u00e3o\" class=\"read-more\" href=\"http:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-interacao-de-neutrons-com-materia-definicao\/\" aria-label=\"More on O que \u00e9 intera\u00e7\u00e3o de n\u00eautrons com mat\u00e9ria &#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 intera\u00e7\u00e3o de n\u00eautrons com mat\u00e9ria - defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"Os n\u00eautrons podem interagir com a mat\u00e9ria de v\u00e1rias maneiras. 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