{"id":21506,"date":"2020-07-20T06:55:15","date_gmt":"2020-07-20T06:55:15","guid":{"rendered":"https:\/\/www.radiation-dosimetry.org\/o-que-e-radiacao-gama-radiacao-gama-definicao\/"},"modified":"2020-07-20T06:57:24","modified_gmt":"2020-07-20T06:57:24","slug":"o-que-e-radiacao-gama-radiacao-gama-definicao","status":"publish","type":"post","link":"http:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-radiacao-gama-radiacao-gama-definicao\/","title":{"rendered":"O que \u00e9 radia\u00e7\u00e3o gama \/ radia\u00e7\u00e3o 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\">Os raios gama, tamb\u00e9m conhecidos como radia\u00e7\u00e3o gama, referem-se \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de energias muito altas. Os raios gama s\u00e3o f\u00f3tons de alta energia. Dosimetria de Radia\u00e7\u00e3o<\/div>\n<\/div>\n<div><\/div>\n<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\">\n<p><strong><span>Os raios gama<\/span><\/strong><span>\u00a0, tamb\u00e9m conhecidos como\u00a0<\/span><strong><span>radia\u00e7\u00e3o gama<\/span><\/strong><span>\u00a0, se referem \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de energias muito altas.\u00a0Os raios gama s\u00e3o\u00a0<\/span><a title=\"F\u00f3ton - Part\u00edcula Fundamental\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/\"><span>f\u00f3tons de<\/span><\/a><span>\u00a0alta energia\u00a0com comprimentos de onda muito curtos e, portanto, frequ\u00eancia muito alta.\u00a0Como os raios gama s\u00e3o em subst\u00e2ncia apenas f\u00f3tons de alta energia, eles s\u00e3o mat\u00e9ria muito penetrante e, portanto, biologicamente perigosos.\u00a0Os raios gama podem viajar milhares de p\u00e9s no ar e podem facilmente passar pelo corpo humano.<\/span><\/p>\n<p><strong><span>Os raios gama<\/span><\/strong><span>\u00a0s\u00e3o emitidos por\u00a0<\/span><a title=\"Estabilidade nuclear\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/nuclear-stability\/\"><span>n\u00facleos inst\u00e1veis<\/span><\/a><span>\u00a0em sua transi\u00e7\u00e3o de um estado de alta energia para um estado inferior, conhecido como decaimento gama.\u00a0Na maioria das fontes pr\u00e1ticas de laborat\u00f3rio, os estados nucleares excitados s\u00e3o criados no decaimento de um radionucl\u00eddeo pai, portanto, um decaimento gama geralmente\u00a0<\/span><strong><span>acompanha outras\u00a0<\/span><a title=\"Formas de radia\u00e7\u00e3o ionizante\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/forms-ionizing-radiation\/\"><span>formas de decaimento<\/span><\/a><\/strong><span>\u00a0, como decaimento alfa ou beta.<\/span><\/p>\n<p><span>Radia\u00e7\u00e3o e tamb\u00e9m raios gama est\u00e3o ao nosso redor.\u00a0Dentro, ao redor e acima do mundo em que vivemos. \u00c9 uma parte do nosso mundo natural que est\u00e1 aqui desde o nascimento do nosso planeta.\u00a0<\/span><strong><span>As fontes naturais de raios gama<\/span><\/strong><span>\u00a0na Terra s\u00e3o, entre outros, raios gama de radionucl\u00eddeos que ocorrem naturalmente, particularmente o pot\u00e1ssio-40.\u00a0O pot\u00e1ssio-40 \u00e9 um is\u00f3topo radioativo de pot\u00e1ssio que tem uma meia-vida muito longa de 1.251 \u00d7 10\u00a0<\/span><sup><span>9<\/span><\/sup><span>\u00a0anos (compar\u00e1vel \u00e0 idade da Terra).\u00a0Este is\u00f3topo pode ser encontrado no solo, \u00e1gua tamb\u00e9m na carne e banana.\u00a0Este n\u00e3o \u00e9 o \u00fanico exemplo de fonte natural de raios gama.<\/span><\/p>\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\">\n<figure id=\"attachment_11840\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-11840\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Barium-137-radionuclide.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11840 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Barium-137-radionuclide-300x300.png\" alt=\"O b\u00e1rio-137m \u00e9 um produto de um produto de fiss\u00e3o comum - c\u00e9sio - 137. O principal raio gama do b\u00e1rio-137m \u00e9 o f\u00f3ton de 661keV.\" width=\"300\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Barium-137-radionuclide-300x300.png\" \/><\/a><figcaption id=\"caption-attachment-11840\" class=\"wp-caption-text\"><span>O b\u00e1rio-137m \u00e9 um produto de um produto de fiss\u00e3o comum &#8211; c\u00e9sio &#8211; 137. O principal raio gama do b\u00e1rio-137m \u00e9 o f\u00f3ton de 661keV.<\/span><\/figcaption><\/figure>\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-spacer\"><\/div>\n<h2><span>Descoberta de raios gama<\/span><\/h2>\n<figure id=\"attachment_11798\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-11798\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/becquerel.png\"><img loading=\"lazy\" class=\"size-full wp-image-11798 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/becquerel.png\" alt=\"Antoine Henri Becquerel\" width=\"168\" height=\"238\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/becquerel.png\" \/><\/a><figcaption id=\"caption-attachment-11798\" class=\"wp-caption-text\"><span>Antoine Henri Becquerel<\/span><\/figcaption><\/figure>\n<p><span>Os raios gama foram descobertos logo ap\u00f3s a descoberta dos raios X.\u00a0Em 1896, o cientista franc\u00eas\u00a0<\/span><strong><span>Henri Becquerel<\/span><\/strong><span>\u00a0descobriu que os minerais de ur\u00e2nio poderiam expor uma placa fotogr\u00e1fica atrav\u00e9s de outro material.\u00a0Becquerel presumiu que o ur\u00e2nio emitisse alguma luz invis\u00edvel semelhante aos raios X, que foram descobertos recentemente pela\u00a0<\/span><strong><span>WCRoentgen<\/span><\/strong><span>\u00a0.\u00a0Ele chamou de &#8221;\u00a0<\/span><strong><span>fosforesc\u00eancia met\u00e1lica<\/span><\/strong><span>\u00a0&#8220;.\u00a0De fato, Henri Becquerel descobriu que\u00a0<\/span><strong><span>a radia\u00e7\u00e3o gama<\/span><\/strong><span>\u00a0\u00e9 emitida pelo radiois\u00f3topo\u00a0<\/span><sup><span>226<\/span><\/sup><span>\u00a0Ra (r\u00e1dio), que faz parte da s\u00e9rie Uranium da cadeia de decaimento do ur\u00e2nio.<\/span><br \/>\n<span>Primeiro, pensou-se que os raios gama eram part\u00edculas com massa, por exemplo,\u00a0<a title=\"Part\u00edcula Beta\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/\">part\u00edculas beta<\/a>\u00a0extremamente energ\u00e9ticas<\/span><span>.\u00a0Essa opini\u00e3o falhou, porque essa radia\u00e7\u00e3o n\u00e3o pode ser desviada por um campo magn\u00e9tico, o que indicava que eles n\u00e3o tinham carga.\u00a0Em 1914, observou-se que os raios gama refletiam-se nas superf\u00edcies de cristal, provando que deveriam ser\u00a0<\/span><strong><span>radia\u00e7\u00e3o eletromagn\u00e9tica<\/span><\/strong><span>\u00a0, mas com maior energia (maior frequ\u00eancia e comprimentos de onda mais curtos).<\/span><\/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=\"su-spacer\"><\/div>\n<h2><span>Caracter\u00edsticas dos Raios Gama \/ Radia\u00e7\u00e3o<\/span><\/h2>\n<\/div>\n<\/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\"><strong><span>Os principais recursos dos raios gama<\/span><\/strong><span>\u00a0est\u00e3o resumidos nos seguintes pontos:<\/span><\/p>\n<ul>\n<li><span>Os raios gama s\u00e3o\u00a0<\/span><strong><span>f\u00f3tons de alta energia<\/span><\/strong><span>\u00a0(cerca de 10.000 vezes mais energia que os f\u00f3tons vis\u00edveis), os mesmos f\u00f3tons que os f\u00f3tons que formam a faixa vis\u00edvel do espectro eletromagn\u00e9tico &#8211; a luz.<\/span><\/li>\n<li><span>F\u00f3tons (raios gama e raios X) podem ionizar \u00e1tomos diretamente (apesar de serem eletricamente neutros) atrav\u00e9s do efeito Fotoel\u00e9trico e do efeito Compton, mas a ioniza\u00e7\u00e3o secund\u00e1ria (indireta) \u00e9 muito mais significativa.<\/span><\/li>\n<li><span>Os raios gama ionizam a mat\u00e9ria principalmente via\u00a0<\/span><strong><span>ioniza\u00e7\u00e3o indireta<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Embora seja conhecido um grande n\u00famero de poss\u00edveis intera\u00e7\u00f5es, existem tr\u00eas mecanismos principais de intera\u00e7\u00e3o com a mat\u00e9ria.<\/span>\n<ul>\n<li><strong><span>Efeito fotoel\u00e9trico<\/span><\/strong><\/li>\n<li><strong><span>Efeito Compton<\/span><\/strong><\/li>\n<li><strong><span>Produ\u00e7\u00e3o de pares<\/span><\/strong><\/li>\n<\/ul>\n<\/li>\n<li><span>Os raios gama viajam\u00a0<\/span><strong><span>na velocidade da luz<\/span><\/strong><span>\u00a0e podem viajar milhares de metros no ar antes de gastar sua energia.<\/span><\/li>\n<li><span>Como a radia\u00e7\u00e3o gama \u00e9 uma mat\u00e9ria muito penetrante, ela deve ser protegida por materiais muito densos, como chumbo ou ur\u00e2nio.<\/span><\/li>\n<li><span>A 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 raios X s\u00e3o emitidos por el\u00e9trons fora do n\u00facleo, enquanto\u00a0<\/span><strong><span>os raios gama s\u00e3o emitidos pelo n\u00facleo<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Os raios gama frequentemente\u00a0<\/span><strong><span>acompanham a emiss\u00e3o<\/span><\/strong><span>\u00a0de\u00a0<a title=\"Part\u00edcula Beta\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/\">radia\u00e7\u00e3o\u00a0<\/a><\/span><a title=\"Alpha Particle\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/alpha-particle\/\"><span>alfa<\/span><\/a><span>\u00a0e\u00a0<\/span><a title=\"Part\u00edcula Beta\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/beta-particle\/\"><span>beta<\/span><\/a><span>\u00a0.<\/span><\/li>\n<\/ul>\n<div class=\"su-accordion su-u-trim\">\n<div class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\"><\/div>\n<\/div>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\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\">\n<figure id=\"attachment_11707\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11707\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/cloud-chamber-2.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11707 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/cloud-chamber-2-300x167.png\" alt=\"Compara\u00e7\u00e3o de part\u00edculas em uma c\u00e2mara de nuvens.  Fonte: wikipedia.org\" width=\"300\" height=\"167\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/cloud-chamber-2-300x167.png\" \/><\/a><figcaption id=\"caption-attachment-11707\" class=\"wp-caption-text\"><span>Compara\u00e7\u00e3o de part\u00edculas em uma c\u00e2mara de nuvens.\u00a0Fonte: wikipedia.org<\/span><\/figcaption><\/figure>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<figure id=\"attachment_11684\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11684\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/total_photon_attenuation.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11684 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/total_photon_attenuation-300x217.png\" alt=\"Coeficientes de atenua\u00e7\u00e3o.\" width=\"300\" height=\"217\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/total_photon_attenuation-300x217.png\" \/><\/a><figcaption id=\"caption-attachment-11684\" class=\"wp-caption-text\"><span>Total de se\u00e7\u00f5es transversais de f\u00f3tons.<\/span><br \/>\n<span>Fonte: Wikimedia Commons<\/span><\/figcaption><\/figure>\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-spacer\"><\/div>\n<h2><span>Efeito fotoel\u00e9trico<\/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<div class=\"su-spoiler-content su-u-clearfix su-u-trim\">\n<figure id=\"attachment_11826\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-11826\"><figcaption id=\"caption-attachment-11826\" class=\"wp-caption-text\"><\/figcaption><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/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\">\n<ul>\n<li><span>O efeito fotoel\u00e9trico domina\u00a0<\/span><strong><span>com baixas energias dos raios gama<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>O efeito fotoel\u00e9trico leva \u00e0\u00a0<\/span><strong><span>emiss\u00e3o de fotoel\u00e9trons<\/span><\/strong><span>\u00a0da mat\u00e9ria quando a luz (\u00a0<\/span><a title=\"F\u00f3ton - Part\u00edcula Fundamental\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/\"><span>f\u00f3tons<\/span><\/a><span>\u00a0) brilha sobre eles.<\/span><\/li>\n<li><span>A energia m\u00e1xima que um el\u00e9tron pode receber em qualquer intera\u00e7\u00e3o \u00e9\u00a0<\/span><strong><i><span>h\u03bd<\/span><\/i><span>\u00a0.<\/span><\/strong><\/li>\n<li><span>Os el\u00e9trons s\u00e3o emitidos apenas pelo efeito fotoel\u00e9trico se o f\u00f3ton atingir ou exceder\u00a0<\/span><strong><span>um limiar de energia<\/span><\/strong><span>\u00a0.<\/span><\/li>\n<li><span>Um el\u00e9tron livre (por exemplo, da nuvem at\u00f4mica) n\u00e3o pode absorver toda a energia do f\u00f3ton incidente.\u00a0Isso \u00e9 resultado da necessidade de economizar impulso e energia.<\/span><\/li>\n<li><span>A se\u00e7\u00e3o transversal para a emiss\u00e3o de n = 1 fotoel\u00e9trons (casca K) \u00e9 maior que a dos n = 2 fotoel\u00e9trons (casca L).\u00a0Isso \u00e9 resultado da necessidade de economizar impulso e energia.<\/span><\/li>\n<\/ul>\n<div class=\"su-spacer\"><\/div>\n<h2><span>Defini\u00e7\u00e3o de efeito fotoel\u00e9trico<\/span><\/h2>\n<p><span>No efeito fotoel\u00e9trico, um f\u00f3ton sofre uma intera\u00e7\u00e3o com um el\u00e9tron que est\u00e1 ligado em um \u00e1tomo.\u00a0Nesta intera\u00e7\u00e3o, o f\u00f3ton incidente desaparece completamente e um fotoel\u00e9tron energ\u00e9tico \u00e9 ejetado pelo \u00e1tomo de uma\u00a0<\/span><strong><span>de suas conchas ligadas<\/span><\/strong><span>\u00a0.\u00a0A energia cin\u00e9tica do fotoel\u00e9tron ejetado (E\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0) \u00e9 igual \u00e0 energia incidente do f\u00f3ton (h\u03bd) menos a\u00a0<\/span><a title=\"Energia de liga\u00e7\u00e3o\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/binding-energy\/\"><span>energia<\/span><\/a><span>\u00a0de\u00a0<a title=\"Energia de liga\u00e7\u00e3o\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/binding-energy\/\">liga\u00e7\u00e3o<\/a>\u00a0do fotoel\u00e9tron em seu inv\u00f3lucro original (E\u00a0<\/span><sub><span>b<\/span><\/sub><span>\u00a0).<\/span><\/p>\n<p><strong><span>E\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0= h\u03bd-E\u00a0<\/span><sub><span>b<\/span><\/sub><\/strong><\/p>\n<p><span>Portanto, os fotoel\u00e9trons s\u00e3o emitidos apenas pelo efeito fotoel\u00e9trico se o f\u00f3ton atingir ou exceder\u00a0<\/span><strong><span>um limiar de energia<\/span><\/strong><span>\u00a0&#8211; a energia de liga\u00e7\u00e3o do el\u00e9tron &#8211;\u00a0<\/span><strong><span>a fun\u00e7\u00e3o<\/span><\/strong><span>\u00a0de\u00a0<strong>trabalho<\/strong>\u00a0do material.\u00a0Para raios gama com energias superiores a centenas de keV, o fotoel\u00e9tron retira a maior parte da energia incidente do f\u00f3ton &#8211; h\u03bd.<\/span><\/p>\n<p><span>Ap\u00f3s uma intera\u00e7\u00e3o fotoel\u00e9trica, um \u00e1tomo absorvedor ionizado \u00e9 criado com\u00a0<\/span><strong><span>uma vaga em uma de suas conchas ligadas<\/span><\/strong><span>\u00a0.\u00a0Essa vaga ser\u00e1 rapidamente preenchida por um el\u00e9tron de uma concha com uma energia de liga\u00e7\u00e3o mais baixa (outras conchas) ou pela captura de um el\u00e9tron livre do material.\u00a0O rearranjo de el\u00e9trons de outras camadas cria outra vaga que, por sua vez, \u00e9 preenchida por um el\u00e9tron de uma camada de energia de liga\u00e7\u00e3o ainda mais baixa.\u00a0Portanto, uma cascata de\u00a0<\/span><strong><span>raios-X<\/span><\/strong><span>\u00a0mais\u00a0<strong>caracter\u00edsticos<\/strong>\u00a0tamb\u00e9m pode ser gerada.\u00a0A probabilidade de emiss\u00e3o caracter\u00edstica de raios-X diminui \u00e0 medida que o n\u00famero at\u00f4mico do absorvedor diminui.\u00a0\u00c0s vezes, a emiss\u00e3o de um el\u00e9tron Auger ocorre.<\/span><\/p>\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\">\n<figure id=\"attachment_11855\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11855\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photoelectric-Effect-Potassium.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-11855 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photoelectric-Effect-Potassium-300x169.jpg\" alt=\"Efeito fotoel\u00e9trico com f\u00f3tons do espectro vis\u00edvel na placa de pot\u00e1ssio - limiar de energia - 2eV\" width=\"300\" height=\"169\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photoelectric-Effect-Potassium-300x169.jpg\" \/><\/a><figcaption id=\"caption-attachment-11855\" class=\"wp-caption-text\"><span>Efeito fotoel\u00e9trico com f\u00f3tons do espectro vis\u00edvel na placa de pot\u00e1ssio &#8211; limiar de energia &#8211; 2eV<\/span><\/figcaption><\/figure>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<figure id=\"attachment_11817\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11817\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photoelectric_effect_2.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-11817 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photoelectric_effect_2-300x170.jpg\" alt=\"Absor\u00e7\u00e3o gama por um \u00e1tomo.  Fonte: laradioactivite.com\/\" width=\"300\" height=\"170\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photoelectric_effect_2-300x170.jpg\" \/><\/a><figcaption id=\"caption-attachment-11817\" class=\"wp-caption-text\"><span>Absor\u00e7\u00e3o gama por um \u00e1tomo.<\/span><br \/>\n<span>Fonte: laradioactivite.com\/<\/span><\/figcaption><\/figure>\n<\/div>\n<\/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\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Se\u00e7\u00f5es Cruzadas de Efeito Fotoel\u00e9trico<\/span><\/h2>\n<p><strong><span>Em pequenos valores de energia de raios gama, o efeito fotoel\u00e9trico domina<\/span><\/strong><span>\u00a0.\u00a0O mecanismo tamb\u00e9m \u00e9 aprimorado para materiais de alto n\u00famero at\u00f4mico Z. N\u00e3o \u00e9 simples derivar express\u00e3o anal\u00edtica para a probabilidade de absor\u00e7\u00e3o fotoel\u00e9trica de raios gama por \u00e1tomo em todas as faixas de energias de raios gama.\u00a0A probabilidade de absor\u00e7\u00e3o fotoel\u00e9trica por unidade de massa \u00e9 aproximadamente proporcional a:<\/span><\/p>\n<p><strong><span>\u03c4\u00a0<\/span><sub><span>(fotoel\u00e9trico)<\/span><\/sub><span>\u00a0= constante x Z\u00a0<\/span><sup><span>N<\/span><\/sup><span>\u00a0\/ E\u00a0<\/span><sup><span>3.5<\/span><\/sup><\/strong><\/p>\n<p><span>onde\u00a0<\/span><strong><span>Z<\/span><\/strong><span>\u00a0\u00e9 o n\u00famero at\u00f4mico, o expoente\u00a0<\/span><strong><span>n<\/span><\/strong><span>\u00a0varia entre 4 e 5.\u00a0<\/span><strong><span>E<\/span><\/strong><span>\u00a0\u00e9 a energia do f\u00f3ton incidente.\u00a0A proporcionalidade para pot\u00eancias mais altas do n\u00famero at\u00f4mico Z \u00e9 a principal raz\u00e3o para o uso de materiais com alto teor de Z, como chumbo ou ur\u00e2nio empobrecido em escudos de raios gama.<\/span><\/p>\n<p><span>Embora a probabilidade de absor\u00e7\u00e3o fotoel\u00e9trica do f\u00f3ton gama diminua, em geral, com o aumento da energia do f\u00f3ton, existem\u00a0<\/span><strong><span>acentuadas descontinuidades<\/span><\/strong><span>\u00a0na curva de se\u00e7\u00e3o transversal.\u00a0Estes s\u00e3o chamados de\u00a0<\/span><strong><span>&#8220;bordas de absoption&#8221;<\/span><\/strong><span>e eles correspondem \u00e0s energias de liga\u00e7\u00e3o dos el\u00e9trons das conchas atadas dos \u00e1tomos.\u00a0Para f\u00f3tons com a energia logo acima da borda, a energia do f\u00f3ton \u00e9 apenas suficiente para sofrer a intera\u00e7\u00e3o fotoel\u00e9trica com o el\u00e9tron da casca ligada, digamos K-shell.\u00a0A probabilidade de tal intera\u00e7\u00e3o est\u00e1 logo acima dessa borda muito maior do que a de f\u00f3tons de energia ligeiramente abaixo dessa borda.\u00a0Para os f\u00f3tons gama abaixo dessa borda, a intera\u00e7\u00e3o com o el\u00e9tron da casca K \u00e9 energeticamente imposs\u00edvel e, portanto, a probabilidade cai abruptamente.\u00a0Essas arestas ocorrem tamb\u00e9m em energias de liga\u00e7\u00e3o de el\u00e9trons de outras camadas (L, M, N &#8230; ..).<\/span><\/p>\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\">\n<figure id=\"attachment_11683\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11683\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/photoelectric_effect.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11683 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/photoelectric_effect-300x214.png\" alt=\"Se\u00e7\u00e3o transversal de efeito fotoel\u00e9trico.\" width=\"300\" height=\"214\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/photoelectric_effect-300x214.png\" \/><\/a><figcaption id=\"caption-attachment-11683\" class=\"wp-caption-text\"><span>Se\u00e7\u00e3o transversal de efeito fotoel\u00e9trico.<\/span><\/figcaption><\/figure>\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-spacer\"><\/div>\n<h2><span>Efeito Compton<\/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-spacer\"><\/div>\n<h2><span>Principais caracter\u00edsticas do Compton Scattering<\/span><\/h2>\n<ul>\n<li><span>A dispers\u00e3o de Compton domina\u00a0<\/span><strong><span>em energias intermedi\u00e1rias.<\/span><\/strong><\/li>\n<li><span>\u00c9 a dispers\u00e3o de f\u00f3tons\u00a0<\/span><strong><span>por el\u00e9trons at\u00f4micos \u00a0<\/span><\/strong><\/li>\n<li><span>Os f\u00f3tons passam por um deslocamento de comprimento de onda chamado\u00a0<\/span><strong><span>deslocamento de Compton.<\/span><\/strong><\/li>\n<li><span>A energia transferida para o el\u00e9tron de recuo pode\u00a0<\/span><strong><span>variar de zero a uma grande fra\u00e7\u00e3o<\/span><\/strong><span>\u00a0da energia incidente de raios gama<\/span><\/li>\n<\/ul>\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-spacer\"><\/div>\n<h2><span>Defini\u00e7\u00e3o de dispers\u00e3o de Compton<\/span><\/h2>\n<p><span>A dispers\u00e3o de Compton \u00e9 a dispers\u00e3o inel\u00e1stica ou n\u00e3o cl\u00e1ssica de um f\u00f3ton (que pode ser um\u00a0<\/span><a title=\"F\u00f3ton - Part\u00edcula Fundamental\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/\"><span>f\u00f3ton de<\/span><\/a><span>\u00a0raios X ou gama\u00a0) por uma part\u00edcula carregada, geralmente um el\u00e9tron.\u00a0Na dispers\u00e3o de Compton, o f\u00f3ton de raios gama incidente \u00e9 desviado atrav\u00e9s de um \u00e2ngulo \u0398 em rela\u00e7\u00e3o \u00e0 sua dire\u00e7\u00e3o original.\u00a0Essa deflex\u00e3o resulta em uma diminui\u00e7\u00e3o na energia (diminui\u00e7\u00e3o na frequ\u00eancia do f\u00f3ton) do f\u00f3ton e \u00e9 chamado de\u00a0<\/span><strong><span>efeito Compton<\/span><\/strong><span>\u00a0.\u00a0O f\u00f3ton transfere uma parte de sua energia para\u00a0<\/span><strong><span>o el\u00e9tron de recuo<\/span><\/strong><span>\u00a0.\u00a0A energia transferida para o el\u00e9tron de recuo pode variar de zero a uma grande fra\u00e7\u00e3o da energia incidente de raios gama, porque todos os \u00e2ngulos de dispers\u00e3o s\u00e3o poss\u00edveis.\u00a0A dispers\u00e3o de Compton foi observada por\u00a0<\/span><strong><span>AHCompton em 1923<\/span><\/strong><span>na Universidade de Washington em St. Louis.\u00a0Compton ganhou\u00a0<\/span><strong><span>o Pr\u00eamio Nobel de F\u00edsica em 1927<\/span><\/strong><span>\u00a0por esse novo entendimento sobre a natureza das part\u00edculas dos f\u00f3tons.<\/span><\/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=\"su-spacer\"><\/div>\n<h2><span>F\u00f3rmula de dispers\u00e3o de Compton<\/span><\/h2>\n<p><span>A f\u00f3rmula de Compton foi publicada em 1923 na Physical Review.\u00a0Compton explicou que o deslocamento dos raios X \u00e9 causado pelo momento de part\u00edculas dos f\u00f3tons.\u00a0A f\u00f3rmula de dispers\u00e3o de Compton \u00e9 a rela\u00e7\u00e3o matem\u00e1tica entre a mudan\u00e7a no comprimento de onda e o \u00e2ngulo de dispers\u00e3o dos raios-X.\u00a0No caso de espalhamento de Compton, o f\u00f3ton de frequ\u00eancia\u00a0<\/span><i><span>f<\/span><\/i><span>\u00a0colide com um el\u00e9tron em repouso.\u00a0Ap\u00f3s a colis\u00e3o, o f\u00f3ton ricocheteia o el\u00e9tron, liberando parte de sua energia inicial (dada pela f\u00f3rmula E = hf de Planck). Enquanto o el\u00e9tron ganha impulso (massa x velocidade), o\u00a0<\/span><strong><span>f\u00f3ton n\u00e3o pode diminuir sua velocidade<\/span><\/strong><span>\u00a0.\u00a0Como resultado da lei de conserva\u00e7\u00e3o do momento, o f\u00f3ton deve diminuir seu momento dado por:<\/span><\/p>\n<p><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photon-momentum-formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-11869 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photon-momentum-formula.png\" alt=\"Como resultado da lei de conserva\u00e7\u00e3o do momento, o f\u00f3ton deve diminuir seu momento dado por esta f\u00f3rmula.\" width=\"177\" height=\"59\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Photon-momentum-formula.png\" \/><\/a><\/p>\n<p><span>Portanto, a diminui\u00e7\u00e3o do momento do f\u00f3ton deve ser traduzida em\u00a0<\/span><strong><span>diminui\u00e7\u00e3o da frequ\u00eancia<\/span><\/strong><span>\u00a0(aumento no comprimento de onda \u0394\u00a0<\/span><b><span>\u03bb = \u03bb &#8216;- \u03bb<\/span><\/b><span>\u00a0).\u00a0A mudan\u00e7a do comprimento de onda aumentou com o \u00e2ngulo de dispers\u00e3o de acordo com\u00a0<\/span><strong><span>a f\u00f3rmula de Compton<\/span><\/strong><span>\u00a0:<\/span><\/p>\n<p><strong><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-Scattering-Formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-11870 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-Scattering-Formula.png\" alt=\"O deslocamento do comprimento de onda aumentou com o \u00e2ngulo de dispers\u00e3o, de acordo com a f\u00f3rmula de Compton\" width=\"236\" height=\"64\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-Scattering-Formula.png\" \/><\/a><\/strong><\/p>\n<figure id=\"attachment_11831\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-11831\"><img src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/compton-scattering.gif\" alt=\"Efeito Compton\" \/><figcaption id=\"caption-attachment-11831\" class=\"wp-caption-text\"><span>Na dispers\u00e3o de Compton, o f\u00f3ton de raios gama incidente \u00e9 desviado atrav\u00e9s de um \u00e2ngulo respect em rela\u00e7\u00e3o \u00e0 sua dire\u00e7\u00e3o original.\u00a0Essa deflex\u00e3o resulta em uma diminui\u00e7\u00e3o na energia (diminui\u00e7\u00e3o na frequ\u00eancia do f\u00f3ton) do f\u00f3ton e \u00e9 chamado de efeito Compton.<\/span><br \/>\n<span>Fonte: hyperphysics.phy-astr.gsu.edu<\/span><\/figcaption><\/figure>\n<p><span>Onde<\/span><\/p>\n<p><b><span>\u03bb<\/span><\/b><span>\u00a0\u00e9 o comprimento de onda inicial do f\u00f3ton<\/span><\/p>\n<p><b><span>\u03bb &#8216;<\/span><\/b><span>\u00a0\u00e9 o comprimento de onda ap\u00f3s a dispers\u00e3o,<\/span><\/p>\n<p><b><span>h<\/span><\/b><span>\u00a0\u00e9 a constante de Planck = 6,626 x 10\u00a0<\/span><sup><span>-34<\/span><\/sup><span>\u00a0Js<\/span><\/p>\n<p><b><span>m\u00a0<\/span><\/b><b><sub><span>e<\/span><\/sub><\/b><span>\u00a0\u00e9 a massa de repouso do el\u00e9tron (0,511 MeV)<\/span><\/p>\n<p><b><span>c<\/span><\/b><span>\u00a0\u00e9 a velocidade da luz<\/span><\/p>\n<p><b><span>\u0398<\/span><\/b><span>\u00a0\u00e9 o \u00e2ngulo de dispers\u00e3o.<\/span><\/p>\n<p><span>A mudan\u00e7a m\u00ednima no comprimento de onda (\u00a0<\/span><i><span>\u03bb \u2032<\/span><\/i><span>\u00a0&#8211;\u00a0<\/span><i><span>\u03bb<\/span><\/i><span>\u00a0) para o f\u00f3ton ocorre quando \u0398 = 0 \u00b0 (cos (\u0398) = 1) e \u00e9 pelo menos zero.\u00a0A varia\u00e7\u00e3o m\u00e1xima no comprimento de onda (\u00a0<\/span><i><span>\u03bb \u2032<\/span><\/i><span>\u00a0&#8211;\u00a0<\/span><i><span>\u03bb<\/span><\/i><span>\u00a0) para o f\u00f3ton ocorre quando \u0398 = 180 \u00b0 (cos (\u0398) = &#8211; 1).\u00a0Neste caso, o f\u00f3ton transfere para o el\u00e9tron o m\u00e1ximo de momento poss\u00edvel. A varia\u00e7\u00e3o m\u00e1xima no comprimento de onda pode ser derivada da f\u00f3rmula de Compton:<\/span><\/p>\n<p><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-length.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-11867 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-length.png\" alt=\"A mudan\u00e7a m\u00e1xima no comprimento de onda pode ser derivada da f\u00f3rmula de Compton.  Comprimento Compton\" width=\"561\" height=\"78\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-length.png\" \/><\/a><\/p>\n<p><span>A quantidade h \/ m\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0c \u00e9 conhecida como\u00a0<\/span><strong><span>comprimento<\/span><\/strong><span>\u00a0de\u00a0<strong>onda<\/strong>\u00a0do el\u00e9tron de\u00a0<strong>Compton<\/strong>\u00a0e \u00e9 igual a\u00a0<\/span><strong><span>2,43 \u00d7 10\u00a0<\/span><sup><span>\u221212<\/span><\/sup><span>\u00a0m<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<\/div>\n<\/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\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Dispers\u00e3o de Compton &#8211; se\u00e7\u00f5es transversais<\/span><\/h2>\n<p><span>A probabilidade de espalhamento de Compton por intera\u00e7\u00e3o com um \u00e1tomo aumenta linearmente com o n\u00famero at\u00f4mico Z, porque depende do n\u00famero de el\u00e9trons dispon\u00edveis para espalhamento no \u00e1tomo alvo.\u00a0<\/span><strong><span>A distribui\u00e7\u00e3o angular<\/span><\/strong><span>\u00a0de f\u00f3tons dispersos a partir de um \u00fanico el\u00e9tron livre \u00e9 descrita pela\u00a0<\/span><strong><span>f\u00f3rmula de Klein-Nishina<\/span><\/strong><span>\u00a0:<\/span><\/p>\n<p><strong><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Klein-Nishina-Formula.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-11868 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Klein-Nishina-Formula.png\" alt=\"A distribui\u00e7\u00e3o angular de f\u00f3tons dispersos a partir de um \u00fanico el\u00e9tron livre \u00e9 descrita pela f\u00f3rmula de Klein-Nishina\" width=\"547\" height=\"85\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Klein-Nishina-Formula.png\" \/><\/a><\/strong><\/p>\n<p><span>onde \u03b5 = E\u00a0<\/span><sub><span>0<\/span><\/sub><span>\u00a0\/ m\u00a0<\/span><sub><span>e<\/span><\/sub><span>\u00a0c\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0e r\u00a0<\/span><sub><span>0<\/span><\/sub><span>\u00a0\u00e9 o &#8220;raio cl\u00e1ssico do el\u00e9tron&#8221; igual a cerca de 2,8 x 10\u00a0<\/span><sup><span>-13<\/span><\/sup><span>\u00a0cm.\u00a0A f\u00f3rmula fornece a probabilidade de espalhar um f\u00f3ton no elemento de \u00e2ngulo s\u00f3lido d\u03a9 = 2\u03c0 sin \u0398 d\u0398 quando a energia incidente \u00e9 E\u00a0<\/span><sub><span>0<\/span><\/sub><span>\u00a0.<\/span><\/p>\n<figure id=\"attachment_11828\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11828\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-scattering-experiment.gif\"><img loading=\"lazy\" class=\"size-full wp-image-11828 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-scattering-experiment.gif\" alt=\"Experi\u00eancia de espalhamento de Compton\" width=\"417\" height=\"544\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-scattering-experiment.gif\" \/><\/a><figcaption id=\"caption-attachment-11828\" class=\"wp-caption-text\"><span>A mudan\u00e7a no comprimento de onda dessa dispers\u00e3o depende apenas do \u00e2ngulo de dispers\u00e3o de uma determinada part\u00edcula alvo.<\/span><br \/>\n<span>Fonte: hyperphysics.phy-astr.gsu.edu\/<\/span><\/figcaption><\/figure>\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\">\n<figure id=\"attachment_11686\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11686\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-scattering.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11686 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-scattering-300x213.png\" alt=\"Efeito Compton\" width=\"300\" height=\"213\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-scattering-300x213.png\" \/><\/a><figcaption id=\"caption-attachment-11686\" class=\"wp-caption-text\"><span>Se\u00e7\u00e3o transversal da dispers\u00e3o de f\u00f3tons por el\u00e9trons por el\u00e9trons at\u00f4micos.<\/span><\/figcaption><\/figure>\n<figure id=\"attachment_11827\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11827\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton_angle_distribution.jpg\"><img loading=\"lazy\" class=\"size-medium wp-image-11827 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton_angle_distribution-300x209.jpg\" alt=\"Espalhamento de Compton - distribui\u00e7\u00e3o de \u00e2ngulos\" width=\"300\" height=\"209\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton_angle_distribution-300x209.jpg\" \/><\/a><figcaption id=\"caption-attachment-11827\" class=\"wp-caption-text\"><span>Energias de um f\u00f3ton a 500 keV e um el\u00e9tron ap\u00f3s a dispers\u00e3o de Compton.<\/span><br \/>\n<span>Fonte: wikipedia.org<\/span><\/figcaption><\/figure>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<\/div>\n<\/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\">\n<div class=\"su-spacer\"><\/div>\n<h2><span>Compton Edge<\/span><\/h2>\n<p><span>Na espectrofotometria,\u00a0<\/span><strong><span>a borda de Compton<\/span><\/strong><span>\u00a0\u00e9 uma caracter\u00edstica do espectr\u00f3grafo que resulta da dispers\u00e3o de Compton no cintilador ou detector.\u00a0Esse recurso \u00e9 devido aos f\u00f3tons que sofrem dispers\u00e3o de Compton com um \u00e2ngulo de dispers\u00e3o de 180 \u00b0 e escapam do detector.\u00a0Quando um raio gama se espalha pelo detector e escapa, apenas uma fra\u00e7\u00e3o de sua energia inicial pode ser depositada na camada sens\u00edvel do detector.\u00a0Depende do \u00e2ngulo de dispers\u00e3o do f\u00f3ton, quanta energia ser\u00e1 depositada no detector.\u00a0Isso leva a um espectro de energias.\u00a0A energia da borda de Compton corresponde ao f\u00f3ton retroespalhado total\u00a0<\/span><strong><span>.<\/span><\/strong><\/p>\n<div class=\"su-spacer\"><\/div>\n<h2><span>Dispers\u00e3o inversa de Compton<\/span><\/h2>\n<p><strong><span>A dispers\u00e3o inversa de Compton<\/span><\/strong><span>\u00a0\u00e9 a dispers\u00e3o de f\u00f3tons de baixa energia para altas energias por el\u00e9trons relativ\u00edsticos.\u00a0Os el\u00e9trons relativ\u00edsticos podem aumentar a energia dos f\u00f3tons de baixa energia em uma quantidade potencialmente enorme (at\u00e9 raios gama podem ser produzidos).\u00a0Este fen\u00f4meno \u00e9 muito importante na astrof\u00edsica.<\/span><\/p>\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\">\n<figure id=\"attachment_11833\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11833\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-edge.gif\"><img loading=\"lazy\" class=\"size-medium wp-image-11833 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-edge-300x245.gif\" alt=\"Borda Compton de 60Co no espectr\u00f4metro gama Na (Tl).\" width=\"300\" height=\"245\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Compton-edge-300x245.gif\" \/><\/a><figcaption id=\"caption-attachment-11833\" class=\"wp-caption-text\"><span>Borda Compton de 60Co no espectr\u00f4metro gama Na (Tl).<\/span><\/figcaption><\/figure>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<figure id=\"attachment_11834\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11834\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Inverse-Compton-scattering.gif\"><img loading=\"lazy\" class=\"size-medium wp-image-11834 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/positron-annihilation-300x165.png\" alt=\"Espalhamento inverso de Compton\" width=\"238\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/positron-annihilation-300x165.png\" \/><\/a><figcaption id=\"caption-attachment-11834\" class=\"wp-caption-text\"><span>fonte: venables.asu.edu<\/span><\/figcaption><\/figure>\n<\/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<div class=\"su-spacer\"><\/div>\n<h2><span>Produ\u00e7\u00e3o de Par Positron-El\u00e9tron<\/span><\/h2>\n<\/div>\n<\/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>Em geral, a\u00a0<\/span><strong><span>produ\u00e7\u00e3o de pares<\/span><\/strong><span>\u00a0\u00e9 um fen\u00f4meno da natureza em que a\u00a0<\/span><strong><span>energia \u00e9 diretamente convertida em mat\u00e9ria<\/span><\/strong><span>\u00a0.\u00a0O fen\u00f4meno da produ\u00e7\u00e3o de pares pode ser visto de duas maneiras diferentes.\u00a0Uma maneira \u00e9 como\u00a0<\/span><strong><span>uma part\u00edcula e antipart\u00edcula<\/span><\/strong><span>\u00a0e a outra \u00e9 como\u00a0<\/span><strong><span>uma part\u00edcula e um buraco<\/span><\/strong><span>\u00a0.\u00a0A primeira maneira pode ser representada pela forma\u00e7\u00e3o de\u00a0<\/span><strong><span>el\u00e9trons e p\u00f3sitrons<\/span><\/strong><span>\u00a0, a partir de um pacote de energia eletromagn\u00e9tica (\u00a0<\/span><strong><span>f\u00f3ton de alta energia &#8211; raios gama<\/span><\/strong><span>\u00a0) viajando atrav\u00e9s da mat\u00e9ria.\u00a0\u00c9 uma das maneiras poss\u00edveis pelas quais os raios gama interagem com a mat\u00e9ria.\u00a0<\/span><strong><span>Em altas energias, essa intera\u00e7\u00e3o domina<\/span><\/strong><span>\u00a0.<\/span><span>Para que ocorra a produ\u00e7\u00e3o de pares el\u00e9tron-p\u00f3sitron, a energia eletromagn\u00e9tica do f\u00f3ton deve estar acima de\u00a0<\/span><strong><span>um limiar de energia<\/span><\/strong><span>\u00a0, equivalente \u00e0 massa restante de dois el\u00e9trons.\u00a0A energia limiar (a massa total de repouso das part\u00edculas produzidas) para a produ\u00e7\u00e3o de pares el\u00e9tron-p\u00f3sitron \u00e9 igual a\u00a0<\/span><strong><span>1,02MeV (2 x 0,511MeV)<\/span><\/strong><span>\u00a0porque a massa restante de um \u00fanico el\u00e9tron \u00e9 equivalente a 0,511MeV de energia.<\/span><\/p>\n<p><span>Se a energia do f\u00f3ton original for maior que 1,02MeV, qualquer energia acima de 1,02MeV estar\u00e1 de acordo com a lei de conserva\u00e7\u00e3o dividida entre a energia cin\u00e9tica de movimento das duas part\u00edculas.<\/span><\/p>\n<p><span>A presen\u00e7a de\u00a0<\/span><strong><span>um campo el\u00e9trico de um \u00e1tomo pesado<\/span><\/strong><span>\u00a0, como chumbo ou ur\u00e2nio,\u00a0<\/span><strong><span>\u00e9 essencial para satisfazer a conserva\u00e7\u00e3o do momento e da energia<\/span><\/strong><span>\u00a0.\u00a0A fim de satisfazer a conserva\u00e7\u00e3o do momento e da energia, o n\u00facleo at\u00f4mico deve receber algum momento.\u00a0Portanto, uma\u00a0produ\u00e7\u00e3o de par de\u00a0<\/span><a title=\"F\u00f3ton - Part\u00edcula Fundamental\" href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/fundamental-particles\/photon\/\"><span>f\u00f3tons\u00a0<\/span><\/a><strong><span>no espa\u00e7o livre n\u00e3o pode ocorrer<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><span>Al\u00e9m disso, o p\u00f3sitron \u00e9 a antipart\u00edcula do el\u00e9tron; portanto, quando um p\u00f3sitron p\u00e1ra, ele interage com outro el\u00e9tron, resultando na aniquila\u00e7\u00e3o de ambas as part\u00edculas e na convers\u00e3o completa de sua massa de repouso em energia pura (de acordo com o E = mc\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0f\u00f3rmula) na forma de dois sentidos opostos 0,511 MeV raios gama (fot\u00f5es).\u00a0O fen\u00f4meno da produ\u00e7\u00e3o de pares est\u00e1, portanto, conectado \u00e0\u00a0<\/span><strong><span>cria\u00e7\u00e3o e destrui\u00e7\u00e3o da mat\u00e9ria<\/span><\/strong><span>\u00a0em uma \u00fanica rea\u00e7\u00e3o.<\/span><\/p>\n<div class=\"su-spacer\"><\/div>\n<h2><span>Produ\u00e7\u00e3o de Par Positron-El\u00e9tron &#8211; Se\u00e7\u00e3o Transversal<\/span><\/h2>\n<p><span>A probabilidade de produ\u00e7\u00e3o de pares, caracterizada pela se\u00e7\u00e3o transversal, \u00e9 uma\u00a0<\/span><strong><span>fun\u00e7\u00e3o muito complicada baseada na mec\u00e2nica qu\u00e2ntica<\/span><\/strong><span>\u00a0.\u00a0Em geral, a se\u00e7\u00e3o transversal aumenta aproximadamente com o quadrado do n\u00famero at\u00f4mico\u00a0<\/span><strong><span>(\u03c3\u00a0<\/span><sub><span>p<\/span><\/sub><span>\u00a0~ Z\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0)<\/span><\/strong><span>\u00a0e aumenta com a energia do f\u00f3ton, mas essa depend\u00eancia \u00e9 muito mais complexa.<\/span><\/p>\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\/Pair-production-in-chamber.jpg\"><img loading=\"lazy\" class=\"aligncenter size-medium wp-image-11706 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Pair-production-in-chamber-216x300.jpg\" alt=\"\" width=\"216\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Pair-production-in-chamber-216x300.jpg\" \/><\/a><\/p>\n<div class=\"su-divider su-divider-style-dotted\"><\/div>\n<figure id=\"attachment_11685\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-11685\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/pair_production.png\"><img loading=\"lazy\" class=\"size-medium wp-image-11685 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/pair_production-300x214.png\" alt=\"Emparelhe a produ\u00e7\u00e3o no campo nuclear e no campo de el\u00e9trons.\" width=\"300\" height=\"214\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/pair_production-300x214.png\" \/><\/a><figcaption id=\"caption-attachment-11685\" class=\"wp-caption-text\"><span>Se\u00e7\u00e3o transversal da produ\u00e7\u00e3o de pares no campo nuclear e no campo de el\u00e9trons.<\/span><\/figcaption><\/figure>\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<h2><span>Atenua\u00e7\u00e3o de raios gama<\/span><\/h2>\n<p><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:<\/span><\/p>\n<p><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 com altas energias.<\/span><\/p>\n<p><span>Com base na defini\u00e7\u00e3o de 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>os raios gama monoenerg\u00e9ticos<\/span><\/strong><span>\u00a0forem colimados em um\u00a0<\/span><strong><span>feixe estreito<\/span><\/strong><span>\u00a0e se o detector atr\u00e1s do material detectar apenas os raios gama que passaram por esse material 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<\/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<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-11791 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\"><span>A import\u00e2ncia relativa de v\u00e1rios processos de intera\u00e7\u00e3o da radia\u00e7\u00e3o gama com a mat\u00e9ria.<\/span><\/figcaption><\/figure>\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 ent\u00e3o 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<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-11792 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\"><span>Depend\u00eancia da intensidade da radia\u00e7\u00e3o gama na espessura do absorvedor<\/span><\/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><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 da massa cm\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0g\u00a0<\/span><sup><span>-1<\/span><\/sup><span>\u00a0.<\/span><\/p>\n<p><span>Para energias intermedi\u00e1rias, o espalhamento 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 pequenos valores de energia de raios gama ou em altos valores 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\u00a0<\/span><sup><span>2<\/span><\/sup><span>\u00a0), o o coeficiente de atenua\u00e7\u00e3o \u03bc n\u00e3o \u00e9 uma constante.<\/span><\/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<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.<\/span><\/p>\n<p><span>A quest\u00e3o \u00e9 bastante simples e pode ser descrita pela seguinte equa\u00e7\u00e3o:<\/span><\/p>\n<p><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\" \/><\/p>\n<p><span>Se a camada de meio valor para a \u00e1gua for 7,15 cm, o coeficiente de atenua\u00e7\u00e3o linear \u00e9:<\/span><\/p>\n<p><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\" \/><\/p>\n<p><span>Agora podemos usar a equa\u00e7\u00e3o de atenua\u00e7\u00e3o exponencial:<\/span><\/p>\n<p><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)\" \/><\/p>\n<p><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)\" \/><\/p>\n<p><span>Portanto<\/span><\/p>\n<p><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)\" \/><\/p>\n<p><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\" \/><\/p>\n<p><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\" \/><\/p>\n<p><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>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<\/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<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<\/span><br \/>\n<span>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<\/span><br \/>\n<span>prevista pela lei exponencial.\u00a0O processo deve ser levado em considera\u00e7\u00e3o ao<\/span><br \/>\n<span>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-11803 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<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\">\n<p>&nbsp;<\/p>\n<\/div>\n<\/div>\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>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=\"https:\/\/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=\"https:\/\/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=\"https:\/\/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<\/div>\n<div><\/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<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Os raios gama, tamb\u00e9m conhecidos como radia\u00e7\u00e3o gama, referem-se \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de energias muito altas. Os raios gama s\u00e3o f\u00f3tons de alta energia. Dosimetria de Radia\u00e7\u00e3o Os raios gama\u00a0, tamb\u00e9m conhecidos como\u00a0radia\u00e7\u00e3o gama\u00a0, se referem \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de energias muito altas.\u00a0Os &#8230; <a title=\"O que \u00e9 radia\u00e7\u00e3o gama \/ radia\u00e7\u00e3o gama &#8211; defini\u00e7\u00e3o\" class=\"read-more\" href=\"http:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-radiacao-gama-radiacao-gama-definicao\/\" aria-label=\"More on O que \u00e9 radia\u00e7\u00e3o gama \/ radia\u00e7\u00e3o 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 radia\u00e7\u00e3o gama \/ radia\u00e7\u00e3o gama - defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"Os raios gama, tamb\u00e9m conhecidos como radia\u00e7\u00e3o gama, referem-se \u00e0 radia\u00e7\u00e3o eletromagn\u00e9tica (sem massa em repouso, sem carga) de energias muito altas. 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