{"id":21866,"date":"2020-07-22T10:24:43","date_gmt":"2020-07-22T10:24:43","guid":{"rendered":"https:\/\/www.radiation-dosimetry.org\/o-que-e-radiacao-natural-de-fundo-definicao\/"},"modified":"2020-07-22T10:26:06","modified_gmt":"2020-07-22T10:26:06","slug":"o-que-e-radiacao-natural-de-fundo-definicao","status":"publish","type":"post","link":"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-radiacao-natural-de-fundo-definicao\/","title":{"rendered":"O que \u00e9 radia\u00e7\u00e3o natural de fundo &#8211; Defini\u00e7\u00e3o"},"content":{"rendered":"<div class=\"su-quote su-quote-style-default\">\n<div class=\"su-quote-inner su-u-clearfix su-u-trim\">A radia\u00e7\u00e3o natural de fundo \u00e9 a radia\u00e7\u00e3o ionizante, origin\u00e1ria de uma variedade de fontes naturais.\u00a0Esta radia\u00e7\u00e3o n\u00e3o est\u00e1 associada a nenhuma atividade humana.\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<p><strong><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Natural-and-Artificial-Radiation-Sources.png\"><img loading=\"lazy\" class=\"alignright size-medium wp-image-25694 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Natural-and-Artificial-Radiation-Sources-300x209.png\" alt=\"Fontes de radia\u00e7\u00e3o natural e artificial\" width=\"300\" height=\"209\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Natural-and-Artificial-Radiation-Sources-300x209.png\" \/><\/a>A radia\u00e7\u00e3o est\u00e1 \u00e0 nossa volta<\/strong>\u00a0.\u00a0Dentro, ao redor e acima do mundo em que vivemos. \u00c9 uma for\u00e7a de energia natural que nos rodeia.\u00a0\u00c9 uma parte do nosso mundo natural que est\u00e1 aqui desde o nascimento do nosso planeta.\u00a0Todas as criaturas vivas, desde o in\u00edcio dos tempos, foram e ainda est\u00e3o sendo expostas a\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/reactor-physics\/atomic-nuclear-physics\/radiation\/ionizing-radiation\/\">radia\u00e7\u00e3o ionizante<\/a>\u00a0.\u00a0A radia\u00e7\u00e3o ionizante \u00e9 gerada por\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-power\/nuclear-reactions\/\">rea\u00e7\u00f5es nucleares<\/a>\u00a0,\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/radioactivity-nuclear-decay\/\">decaimento nuclear<\/a>\u00a0, por temperaturas muito altas ou por acelera\u00e7\u00e3o de part\u00edculas carregadas em campos eletromagn\u00e9ticos.<\/p>\n<h2>Radia\u00e7\u00e3o de fundo natural<\/h2>\n<p>A radia\u00e7\u00e3o natural de fundo \u00e9 a radia\u00e7\u00e3o ionizante, origin\u00e1ria de uma variedade de fontes naturais.\u00a0Todas as criaturas vivas, desde o in\u00edcio dos tempos, foram e ainda est\u00e3o sendo expostas a\u00a0<strong>radia\u00e7\u00e3o ionizante<\/strong>\u00a0.\u00a0Esta radia\u00e7\u00e3o n\u00e3o est\u00e1 associada a nenhuma atividade humana.\u00a0Existem is\u00f3topos radioativos em nossos corpos, casas, ar, \u00e1gua e no solo.\u00a0Todos n\u00f3s tamb\u00e9m estamos expostos \u00e0 radia\u00e7\u00e3o do espa\u00e7o sideral.<\/p>\n<h3>Fontes de radia\u00e7\u00e3o natural de fundo<\/h3>\n<p>Dividimos todas essas fontes naturais de radia\u00e7\u00e3o em tr\u00eas grupos:<\/p>\n<ul>\n<li><strong><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/cosmic-radiation-cosmic-rays\/\">Radia\u00e7\u00e3o C\u00f3smica<\/a><\/strong><\/li>\n<li><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/terrestrial-radiation\/\"><strong>Radia\u00e7\u00e3o Terrestre<\/strong><\/a><\/li>\n<li><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/internal-source-of-radiation\/\"><strong>Radia\u00e7\u00e3o Interna<\/strong><\/a><\/li>\n<\/ul>\n<h2>Radia\u00e7\u00e3o C\u00f3smica<\/h2>\n<figure id=\"attachment_25692\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-25692\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Cosmic-Radiation-Natural-Source-of-Radiation-min.png\"><img loading=\"lazy\" class=\"size-medium wp-image-25692 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Cosmic-Radiation-Natural-Source-of-Radiation-min-300x199.png\" alt=\"Radia\u00e7\u00e3o C\u00f3smica - Fonte Natural de Radia\u00e7\u00e3o\" width=\"300\" height=\"199\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/Cosmic-Radiation-Natural-Source-of-Radiation-min-300x199.png\" \/><\/a><figcaption id=\"caption-attachment-25692\" class=\"wp-caption-text\">Fonte: nasa.gov Licen\u00e7a: Public Domain<\/figcaption><\/figure>\n<p>A radia\u00e7\u00e3o c\u00f3smica refere-se a fontes de radia\u00e7\u00e3o na forma de raios c\u00f3smicos que v\u00eam do sol ou do espa\u00e7o sideral.\u00a0No n\u00edvel do solo, os\u00a0\u00a0<strong>m\u00faons<\/strong>\u00a0, com energias principalmente entre 1 e 20 GeV, contribuem com cerca de 75% da taxa de dose absorvida no ar livre.\u00a0O restante vem de el\u00e9trons produzidos pelos m\u00faons ou presentes na cascata eletromagn\u00e9tica.\u00a0A\u00a0<a href=\"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-dose-eficaz-definicao\/\">dose<\/a>\u00a0anual de raios c\u00f3smicos\u00a0\u00a0\u00a0ao n\u00edvel do mar \u00e9 de cerca de\u00a0\u00a0<strong>0,27 mSv<\/strong>\u00a0\u00a0(27 mrem).\u00a0Se voc\u00ea mora em eleva\u00e7\u00f5es mais altas ou \u00e9 um passageiro frequente de uma companhia a\u00e9rea, essa exposi\u00e7\u00e3o pode ser significativamente maior, pois a atmosfera \u00e9 mais fina aqui.\u00a0Os efeitos do\u00a0\u00a0<strong>campo magn\u00e9tico da Terra<\/strong>\u00a0\u00a0tamb\u00e9m determinam a dose da\u00a0\u00a0<strong>radia\u00e7\u00e3o c\u00f3smica<\/strong>\u00a0.<\/p>\n<p>A radia\u00e7\u00e3o c\u00f3smica pode ser dividida em diferentes tipos de acordo com sua origem.\u00a0Existem tr\u00eas fontes principais dessa radia\u00e7\u00e3o:<\/p>\n<ul>\n<li><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/cosmic-radiation-cosmic-rays\/solar-cosmic-radiation\/\"><strong>Radia\u00e7\u00e3o C\u00f3smica Solar<\/strong><\/a>\u00a0.\u00a0A radia\u00e7\u00e3o c\u00f3smica solar refere-se a fontes de radia\u00e7\u00e3o na forma de part\u00edculas de alta energia (predominantemente pr\u00f3tons) emitidas pelo sol, principalmente em eventos de part\u00edculas solares (SPEs).<\/li>\n<li><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/cosmic-radiation-cosmic-rays\/galactic-cosmic-radiation-gcr\/\"><strong>Radia\u00e7\u00e3o C\u00f3smica Gal\u00e1ctica<\/strong><\/a>\u00a0.\u00a0A radia\u00e7\u00e3o c\u00f3smica gal\u00e1ctica, GCR, refere-se a fontes de radia\u00e7\u00e3o na forma de part\u00edculas de alta energia origin\u00e1rias fora do sistema solar, mas geralmente de dentro da nossa gal\u00e1xia Via L\u00e1ctea.<\/li>\n<li>Radia\u00e7\u00e3o dos cintur\u00f5es de radia\u00e7\u00e3o da Terra (cintur\u00f5es de\u00a0<strong>van Allen<\/strong>\u00a0).\u00a0<strong><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/cosmic-radiation-cosmic-rays\/van-allen-belts\/\">As<\/a>\u00a0correias de\u00a0<a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/cosmic-radiation-cosmic-rays\/van-allen-belts\/\">radia\u00e7\u00e3o Van Allen<\/a>\u00a0s\u00e3o\u00a0<\/strong>\u00a0zonas de part\u00edculas de alta energia (especialmente pr\u00f3tons) presas pelo campo magn\u00e9tico da Terra.<\/li>\n<\/ul>\n<h3><span id=\"Dose_Rate_in_Airplane_8211_Radiation_in_Flight\"><span>Fundo natural no avi\u00e3o &#8211; radia\u00e7\u00e3o em voo<\/span><\/span><\/h3>\n<p><span>A exposi\u00e7\u00e3o \u00e0\u00a0\u00a0<\/span><strong><span>radia\u00e7\u00e3o c\u00f3smica<\/span><\/strong><span>\u00a0\u00a0aumenta rapidamente com a altitude.\u00a0Em v\u00f4o, h\u00e1 duas fontes principais de radia\u00e7\u00e3o natural a serem consideradas: os\u00a0\u00a0<\/span><strong><span>Raios C\u00f3smicos Gal\u00e1cticos,<\/span><\/strong><span>\u00a0\u00a0sempre presentes, e os Eventos de Pr\u00f3ton Solar, \u00e0s vezes chamados de eventos do Raio C\u00f3smico Solar (SCR), que ocorrem esporadicamente.\u00a0A taxa de dose da radia\u00e7\u00e3o c\u00f3smica varia em diferentes partes do mundo e depende fortemente do campo geomagn\u00e9tico, altitude e ciclo solar.\u00a0O campo de radia\u00e7\u00e3o nas altitudes das aeronaves consiste em n\u00eautrons, pr\u00f3tons e pions.\u00a0Em v\u00f4o, os\u00a0\u00a0<\/span><strong><span>n\u00eautrons contribuem com 40 &#8211; 80%<\/span><\/strong><span>\u00a0\u00a0da\u00a0\u00a0<\/span><a href=\"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-dose-equivalente-definicao\/\"><span>dose equivalente<\/span><\/a><span>, dependendo do campo geomagn\u00e9tico, altitude e ciclo solar.\u00a0A taxa de dose de radia\u00e7\u00e3o c\u00f3smica nos avi\u00f5es \u00e9 t\u00e3o alta (mas n\u00e3o perigosa) que, de acordo com o Relat\u00f3rio das Na\u00e7\u00f5es Unidas UNSCEAR 2000, os funcion\u00e1rios das equipes de avia\u00e7\u00e3o recebem mais dose, em m\u00e9dia, do que qualquer outro trabalhador, inclusive os das usinas nucleares.<\/span><\/p>\n<p><span>A taxa de dose no n\u00edvel do solo \u00e9, em m\u00e9dia, de 0,10 \u03bcSv \/ h, mas na altitude m\u00e1xima de v\u00f4o (8,8 km ou 29.000 p\u00e9s), pode atingir cerca de\u00a0\u00a0<\/span><strong><span>2,0 \u03bcSv \/ h<\/span><\/strong><span>\u00a0\u00a0(ou valores ainda mais altos).\u00a0Uma taxa de dose de\u00a0\u00a0<\/span><strong><span>4 \u03bcSv \/ h<\/span><\/strong><span>\u00a0\u00a0pode ser usada para representar a taxa m\u00e9dia de dose para todos os voos de longo curso (devido a maiores altitudes).\u00a0Deve-se acrescentar que, para avi\u00f5es supers\u00f4nicos como o Concorde, que poderiam realizar um v\u00f4o transatl\u00e2ntico em 3,5 horas, a taxa de exposi\u00e7\u00e3o (cerca de\u00a0\u00a0<\/span><strong><span>9 \u03bcSv \/ h<\/span><\/strong><span>\u00a0) na altitude de 18 km foi aumentada o suficiente para resultar na mesma exposi\u00e7\u00e3o a raios c\u00f3smicos por cruzando como nos jatos convencionais, rodando cerca de 8 km.<\/span><\/p>\n<h3 class=\"entry-title\"><span>Campo Magn\u00e9tico da Terra como Escudo de Radia\u00e7\u00e3o<\/span><\/h3>\n<figure id=\"attachment_25691\" class=\"wp-caption alignright\"><figcaption class=\"wp-caption-text\"><\/figcaption><\/figure>\n<figure id=\"attachment_25691\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-25691\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/magnetosphere-earth-magnetic-field.png\"><img loading=\"lazy\" class=\"size-medium wp-image-25691 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/magnetosphere-earth-magnetic-field-281x300.png\" alt=\"magnetosfera - campo magn\u00e9tico da terra\" width=\"281\" height=\"300\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/magnetosphere-earth-magnetic-field-281x300.png\" \/><\/a><figcaption id=\"caption-attachment-25691\" class=\"wp-caption-text\"><span>Renderiza\u00e7\u00e3o art\u00edstica da estrutura de uma magnetosfera: 1) Choque de arco.\u00a02) Magnetosheath.\u00a03) Magnetopausa.\u00a04) Magnetosfera.\u00a05) Lobo da cauda norte.\u00a06) Lobo da cauda sul.\u00a07) Plasmasfera.\u00a0Fonte: nasa.gov Licen\u00e7a: Public Domain<\/span><\/figcaption><\/figure>\n<p><strong><span>O campo magn\u00e9tico da Terra<\/span><\/strong><span>\u00a0\u00a0fornece um escudo de radia\u00e7\u00e3o vital da radia\u00e7\u00e3o c\u00f3smica.\u00a0Al\u00e9m de uma atmosfera protetora, tamb\u00e9m temos sorte de a Terra ter um campo magn\u00e9tico.\u00a0O campo magn\u00e9tico se estende a dezenas de milhares de quil\u00f4metros no espa\u00e7o, protegendo a Terra das part\u00edculas carregadas do vento solar e dos raios c\u00f3smicos que, de outra forma, removeriam a atmosfera superior, incluindo a camada de oz\u00f4nio que protege a Terra da radia\u00e7\u00e3o ultravioleta prejudicial.\u00a0Ele nos protege dos efeitos totais do vento solar e da GCR.\u00a0Sem essa prote\u00e7\u00e3o, a biosfera da Terra pode n\u00e3o existir como existe hoje, ou seria pelo menos limitada \u00e0 subsuperf\u00edcie.\u00a0O campo magn\u00e9tico da Terra tamb\u00e9m fornece um escudo de radia\u00e7\u00e3o para os astronautas e a pr\u00f3pria ISS, porque est\u00e1 em baixa \u00f3rbita da Terra.<\/span><\/p>\n<p><span>C\u00e1lculos da perda de di\u00f3xido de carbono da atmosfera de Marte, resultante da elimina\u00e7\u00e3o de \u00edons pelo vento solar, indicam que a dissipa\u00e7\u00e3o do campo magn\u00e9tico de Marte causou uma perda quase total de sua atmosfera.<\/span><\/p>\n<h2><span>Radia\u00e7\u00e3o Terrestre<\/span><\/h2>\n<p><span>Radia\u00e7\u00e3o terrestre refere-se a fontes de radia\u00e7\u00e3o que est\u00e3o no solo, na \u00e1gua e na vegeta\u00e7\u00e3o.\u00a0Os principais is\u00f3topos preocupantes da radia\u00e7\u00e3o terrestre s\u00e3o o ur\u00e2nio e os produtos de decomposi\u00e7\u00e3o do ur\u00e2nio, como t\u00f3rio, r\u00e1dio e r\u00e1don.\u00a0A taxa de dose m\u00e9dia que se origina dos nucl\u00eddeos terrestres (exceto a exposi\u00e7\u00e3o ao rad\u00f4nio) \u00e9 de cerca de\u00a0\u00a0<\/span><strong><span>0,057 \u00b5Gy \/ h.\u00a0<\/span><\/strong><span>Os valores m\u00e1ximos foram medidos na areia de monazita em Guarapari, Brasil (at\u00e9 50 \u00b5Gy \/ hora e em Kerala, \u00cdndia (cerca de 2 \u00b5Gy \/ hora), e em rochas com alta concentra\u00e7\u00e3o de r\u00e1dio em Ramsar, Ir\u00e3 (de 1 a 10 \u00b5Gy \/ hr).<\/span><\/p>\n<figure id=\"attachment_25769\" class=\"wp-caption aligncenter\" aria-describedby=\"caption-attachment-25769\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/radon-mitigation-house.png\"><img loading=\"lazy\" class=\"size-medium wp-image-25769 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/radon-mitigation-house-300x249.png\" alt=\"rad\u00e3o - mitiga\u00e7\u00e3o - casa\" width=\"300\" height=\"249\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/radon-mitigation-house-300x249.png\" \/><\/a><figcaption id=\"caption-attachment-25769\" class=\"wp-caption-text\"><span>O g\u00e1s rad\u00f4nio pode penetrar na casa atrav\u00e9s de rachaduras (devido a um efeito de chamin\u00e9) no ch\u00e3o e nas paredes do por\u00e3o.\u00a0Fonte: suro.cz<\/span><\/figcaption><\/figure>\n<p><span>A dose m\u00e9dia anual de radia\u00e7\u00e3o para uma pessoa a partir de\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/sources-of-radiation\/radon-health-effects-health-risks\/\"><span>rad\u00f4nio<\/span><\/a><span>\u00a0\u00e9 de cerca de\u00a0\u00a0<\/span><strong><span>2 mSv \/ ano<\/span><\/strong><span>\u00a0\u00a0e pode variar em v\u00e1rias ordens de magnitude de um lugar para outro.\u00a0O rad\u00f4nio \u00e9 t\u00e3o importante que geralmente \u00e9 tratado separadamente.\u00a0<\/span><strong><span>O r\u00e1don<\/span><\/strong><span>\u00a0\u00a0\u00e9 um\u00a0<\/span><strong><span>g\u00e1s nobre<\/span><\/strong><span>\u00a0incolor, inodoro e ins\u00edpido\u00a0\u00a0, que escorre continuamente da rocha, mas pode, devido \u00e0 sua alta densidade, acumular-se em casas com pouca ventila\u00e7\u00e3o.\u00a0O fato de o\u00a0\u00a0<\/span><strong><span>rad\u00f4nio ser g\u00e1s<\/span><\/strong><span>\u00a0\u00a0desempenha um papel crucial na dissemina\u00e7\u00e3o de todos os seus n\u00facleos filhos.\u00a0O Simply Radon \u00e9 um meio de transporte da rocha para a atmosfera (ou dentro de edif\u00edcios) por seus produtos de decaimento de curta dura\u00e7\u00e3o (\u00a0<\/span><strong><span>Pb-210<\/span><\/strong><span>\u00a0\u00a0e\u00a0\u00a0<\/span><strong><span>Po-210<\/span><\/strong><span>\u00a0), que apresentam muito mais riscos \u00e0 sa\u00fade.<\/span><\/p>\n<h2><span>Radia\u00e7\u00e3o Interna<\/span><\/h2>\n<p><span>Al\u00e9m das fontes c\u00f3smicas e terrestres, todas as pessoas tamb\u00e9m t\u00eam pot\u00e1ssio radioativo-40, carbono-14, chumbo-210 e outros is\u00f3topos dentro de seus corpos desde o nascimento.<\/span><\/p>\n<p><span>Esses is\u00f3topos s\u00e3o especialmente\u00a0\u00a0<\/span><strong><span>pot\u00e1ssio-40<\/span><\/strong><span>\u00a0, carbono-14 e tamb\u00e9m os is\u00f3topos de ur\u00e2nio e t\u00f3rio.\u00a0A varia\u00e7\u00e3o na dose de radia\u00e7\u00e3o de uma pessoa para outra n\u00e3o \u00e9 t\u00e3o grande quanto a varia\u00e7\u00e3o na dose de fontes c\u00f3smicas e terrestres.\u00a0A dose m\u00e9dia anual de radia\u00e7\u00e3o para uma pessoa de materiais radioativos internos que n\u00e3o o r\u00e1don \u00e9 de cerca de\u00a0\u00a0<\/span><strong><span>0,3 mSv \/ ano,<\/span><\/strong><span>\u00a0\u00a0dos quais:<\/span><\/p>\n<ul>\n<li><span>0,2 mSv \/ ano vem de pot\u00e1ssio-40,<\/span><\/li>\n<li><span>0,12 mSv \/ ano prov\u00e9m das s\u00e9ries de ur\u00e2nio e t\u00f3rio,<\/span><\/li>\n<li><span>12 \u03bcSv \/ ano vem do carbono-40.<\/span><\/li>\n<\/ul>\n<h2><span>Radia\u00e7\u00e3o de fundo e riscos \u00e0 sa\u00fade<\/span><\/h2>\n<p><span>Voc\u00ea n\u00e3o pode passar a vida sem radia\u00e7\u00e3o.\u00a0O perigo de radia\u00e7\u00e3o ionizante reside no fato de que a radia\u00e7\u00e3o \u00e9 invis\u00edvel e n\u00e3o diretamente detect\u00e1vel pelos sentidos humanos.\u00a0As pessoas n\u00e3o podem ver nem sentir radia\u00e7\u00e3o, mas ela deposita energia nas mol\u00e9culas do corpo.<\/span><\/p>\n<figure id=\"attachment_25656\" class=\"wp-caption alignright\" aria-describedby=\"caption-attachment-25656\"><a href=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/LNT-Model-and-Hormesis-Model.png\"><img loading=\"lazy\" class=\"size-medium wp-image-25656 lazy-loaded\" src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/LNT-Model-and-Hormesis-Model-300x276.png\" alt=\"Modelo LNT e Modelo Hormesis\" width=\"300\" height=\"276\" data-lazy-type=\"image\" data-src=\"https:\/\/www.radiation-dosimetry.org\/wp-content\/uploads\/2019\/12\/LNT-Model-and-Hormesis-Model-300x276.png\" \/><\/a><figcaption id=\"caption-attachment-25656\" class=\"wp-caption-text\"><span>Pressupostos alternativos para a extrapola\u00e7\u00e3o do risco de c\u00e2ncer vs. dose de radia\u00e7\u00e3o para n\u00edveis de dose baixa, considerando um risco conhecido em dose alta: modelo LNT e modelo hormesis.<\/span><\/figcaption><\/figure>\n<p><span>Mas\u00a0<\/span><strong><span>n\u00e3o se preocupe<\/span><\/strong><span>\u00a0, as doses da radia\u00e7\u00e3o de fundo geralmente s\u00e3o\u00a0\u00a0<\/span><strong><span>muito pequenas<\/span><\/strong><span>\u00a0(exceto a exposi\u00e7\u00e3o ao rad\u00f4nio).\u00a0Dose baixa aqui significa doses pequenas adicionais compar\u00e1veis \u200b\u200b\u00e0\u00a0<\/span><strong><span>radia\u00e7\u00e3o<\/span><\/strong><span>\u00a0normal de\u00a0\u00a0<strong>fundo<\/strong>\u00a0\u00a0(\u00a0<\/span><strong><span>10 \u00b5Sv<\/span><\/strong><span>\u00a0\u00a0= dose di\u00e1ria m\u00e9dia recebida de fundo natural).\u00a0O problema \u00e9 que, em doses muito baixas, \u00e9 praticamente imposs\u00edvel correlacionar qualquer irradia\u00e7\u00e3o com certos efeitos biol\u00f3gicos.\u00a0Isso ocorre porque a taxa de c\u00e2ncer de linha de base j\u00e1 \u00e9 muito alta e o risco de desenvolver c\u00e2ncer flutua 40% devido ao estilo de vida individual e aos efeitos ambientais, obscurecendo os efeitos sutis da radia\u00e7\u00e3o de baixo n\u00edvel.<\/span><\/p>\n<p><span>Em segundo lugar, e isso \u00e9 crucial, a verdade sobre os efeitos na sa\u00fade de baixa dose de radia\u00e7\u00e3o ainda precisa ser encontrada.\u00a0N\u00e3o se sabe exatamente se essas baixas doses de radia\u00e7\u00e3o s\u00e3o prejudiciais ou ben\u00e9ficas (e onde est\u00e1 o limiar).\u00a0Os \u00f3rg\u00e3os governamentais e reguladores assumem um modelo LNT em vez de um limiar ou hormesis, n\u00e3o porque \u00e9 o mais convincente cientificamente, mas porque \u00e9 a\u00a0<\/span><strong><span>estimativa mais conservadora<\/span><\/strong><span>\u00a0.\u00a0O problema desse modelo \u00e9 que ele negligencia uma s\u00e9rie de\u00a0<\/span><strong><span>processos biol\u00f3gicos<\/span><\/strong><span>\u00a0de\u00a0\u00a0<strong>defesa<\/strong>\u00a0\u00a0que podem ser cruciais\u00a0\u00a0<\/span><strong><span>em baixas doses<\/span><\/strong><span>\u00a0.\u00a0A pesquisa nas \u00faltimas duas d\u00e9cadas \u00e9 muito interessante e mostra que pequenas doses de radia\u00e7\u00e3o administradas a uma taxa de dose baixa\u00a0\u00a0<\/span><strong><span>estimulam os mecanismos de defesa<\/span><\/strong><span>.\u00a0Portanto, o modelo LNT n\u00e3o \u00e9 universalmente aceito, com alguns propondo uma rela\u00e7\u00e3o dose-resposta adaptativa, em que baixas doses s\u00e3o protetoras e altas s\u00e3o prejudiciais.\u00a0Muitos estudos contradizem o modelo LNT e muitos deles mostraram resposta adaptativa a baixas doses de radia\u00e7\u00e3o, resultando em muta\u00e7\u00f5es e c\u00e2nceres reduzidos.\u00a0Este fen\u00f4meno \u00e9 conhecido como\u00a0\u00a0<\/span><strong><span>hormesis de radia\u00e7\u00e3o<\/span><\/strong><span>\u00a0.<\/span><\/p>\n<p><span>De acordo com a\u00a0hip\u00f3tese\u00a0da\u00a0<\/span><strong><span>radia\u00e7\u00e3o hormonal<\/span><\/strong><span>\u00a0, a exposi\u00e7\u00e3o \u00e0 radia\u00e7\u00e3o compar\u00e1vel e logo acima do n\u00edvel natural de radia\u00e7\u00e3o de fundo n\u00e3o \u00e9 prejudicial, mas ben\u00e9fica, embora se aceite que n\u00edveis muito mais altos de radia\u00e7\u00e3o s\u00e3o perigosos.\u00a0Os argumentos para a hormesis est\u00e3o centrados em alguns estudos epidemiol\u00f3gicos em larga escala e nas evid\u00eancias de experimentos de irradia\u00e7\u00e3o animal, mas principalmente nos recentes avan\u00e7os no conhecimento da resposta adaptativa.\u00a0Os proponentes da hormesis de radia\u00e7\u00e3o geralmente afirmam que as respostas de prote\u00e7\u00e3o radiofotogr\u00e1fica nas c\u00e9lulas e no sistema imunol\u00f3gico n\u00e3o apenas combatem os efeitos nocivos da radia\u00e7\u00e3o, mas tamb\u00e9m agem para inibir o c\u00e2ncer espont\u00e2neo n\u00e3o relacionado \u00e0 exposi\u00e7\u00e3o \u00e0 radia\u00e7\u00e3o.<\/span><\/p>\n<p><span>Veja tamb\u00e9m:\u00a0<\/span><a href=\"https:\/\/www.nuclear-power.com\/nuclear-engineering\/radiation-protection\/radiobiology\/linear-no-threshold-model\/\"><span>Modelo LNT<\/span><\/a><\/p>\n<\/div>\n<\/div>\n<p>&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;&#8230;.<\/p>\n<p>Este artigo \u00e9 baseado na tradu\u00e7\u00e3o autom\u00e1tica do artigo original em ingl\u00eas. Para mais informa\u00e7\u00f5es, consulte o artigo em ingl\u00eas. Voc\u00ea pode nos ajudar. Se voc\u00ea deseja corrigir a tradu\u00e7\u00e3o, envie-a para: translations@nuclear-power.com ou preencha o formul\u00e1rio de tradu\u00e7\u00e3o on-line. Agradecemos sua ajuda, atualizaremos a tradu\u00e7\u00e3o o mais r\u00e1pido poss\u00edvel. Obrigado.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A radia\u00e7\u00e3o natural de fundo \u00e9 a radia\u00e7\u00e3o ionizante, origin\u00e1ria de uma variedade de fontes naturais.\u00a0Esta radia\u00e7\u00e3o n\u00e3o est\u00e1 associada a nenhuma atividade humana.\u00a0Dosimetria de Radia\u00e7\u00e3o A radia\u00e7\u00e3o est\u00e1 \u00e0 nossa volta\u00a0.\u00a0Dentro, ao redor e acima do mundo em que vivemos. \u00c9 uma for\u00e7a de energia natural que nos rodeia.\u00a0\u00c9 uma parte do nosso mundo &#8230; <a title=\"O que \u00e9 radia\u00e7\u00e3o natural de fundo &#8211; Defini\u00e7\u00e3o\" class=\"read-more\" href=\"https:\/\/www.radiation-dosimetry.org\/pt-br\/o-que-e-radiacao-natural-de-fundo-definicao\/\" aria-label=\"More on O que \u00e9 radia\u00e7\u00e3o natural de fundo &#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 natural de fundo - Defini\u00e7\u00e3o<\/title>\n<meta name=\"description\" content=\"A radia\u00e7\u00e3o natural de fundo \u00e9 a radia\u00e7\u00e3o ionizante, origin\u00e1ria de uma variedade de fontes naturais. 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