{"id":2904,"date":"2026-05-12T22:47:43","date_gmt":"2026-05-12T19:47:43","guid":{"rendered":"https:\/\/cedra.academy\/?p=2904"},"modified":"2026-08-25T22:54:11","modified_gmt":"2026-08-25T19:54:11","slug":"elementele-radioactive-nucleul-atomic-si-radioactivitatea","status":"publish","type":"post","link":"https:\/\/cedra.academy\/?p=2904","title":{"rendered":"Elementele radioactive. Nucleul atomic \u0219i radioactivitatea"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n
<\/object>Elemente radioactive PREZENTARE ……<\/a>Descarc\u0103<\/a><\/div>\n\n\n\n

<\/h1>\n\n\n\n

1. Nucleul atomic<\/h3>\n\n\n\n

Atomul este alc\u0103tuit dintr-un nucleu atomic<\/strong> \u0219i electroni care se afl\u0103 \u00een jurul acestuia. Nucleul este foarte mic \u00een compara\u021bie cu dimensiunea atomului, dar con\u021bine aproape \u00eentreaga mas\u0103 a atomului.<\/p>\n\n\n\n

Nucleul este format din:<\/p>\n\n\n\n

    \n
  • protoni<\/strong> \u2013 particule cu sarcin\u0103 electric\u0103 pozitiv\u0103;<\/li>\n\n\n\n
  • neutroni<\/strong> \u2013 particule neutre, f\u0103r\u0103 sarcin\u0103 electric\u0103.<\/li>\n<\/ul>\n\n\n\n

    Protonii \u0219i neutronii se numesc \u00eempreun\u0103 nucleoni<\/strong>.<\/p>\n\n\n\n

    Num\u0103rul de protoni din nucleu determin\u0103 num\u0103rul atomic (Z)<\/strong> \u0219i stabile\u0219te ce element chimic este reprezentat. De exemplu, toate nucleele care con\u021bin 92 de protoni apar\u021bin elementului uraniu<\/strong>.<\/p>\n\n\n\n

    Num\u0103rul total de protoni \u0219i neutroni reprezint\u0103 num\u0103rul de mas\u0103 (A)<\/strong>:<\/p>\n\n\n\n

    A = Z + N<\/strong><\/p>\n\n\n\n

    unde Z<\/strong> este num\u0103rul protonilor, iar N<\/strong> \u2013 num\u0103rul neutronilor.<\/p>\n\n\n\n

    2. Ce este radioactivitatea?<\/h3>\n\n\n\n

    Unele nuclee atomice sunt instabile<\/strong>. Ele se transform\u0103 spontan \u00een nuclee mai stabile \u0219i emit \u00een acest proces radia\u021bii<\/strong>. Fenomenul se nume\u0219te radioactivitate<\/strong>.<\/p>\n\n\n\n

    Radioactivitatea a fost descoperit\u0103 \u00een anul 1896 de fizicianul francez Henri Becquerel<\/strong>, iar cercet\u0103rile asupra fenomenului au fost continuate de Marie \u0219i Pierre Curie<\/strong>.<\/p>\n\n\n\n

    Transformarea unui nucleu instabil \u00eentr-un alt nucleu se nume\u0219te dezintegrare radioactiv\u0103<\/strong>.<\/p>\n\n\n\n

    Radioactivitatea poate fi:<\/p>\n\n\n\n

      \n
    • natural\u0103<\/strong> \u2013 \u00eent\u00e2lnit\u0103 \u00een natur\u0103, de exemplu la uraniu, toriu \u0219i radiu;<\/li>\n\n\n\n
    • artificial\u0103<\/strong> \u2013 ob\u021binut\u0103 prin transform\u0103ri nucleare produse de om.<\/li>\n<\/ul>\n\n\n\n

      3. Principalele tipuri de radia\u021bii<\/h3>\n\n\n\n

      \u00cen urma dezintegr\u0103rii radioactive pot fi emise trei tipuri principale de radia\u021bii:<\/p>\n\n\n\n

      Radia\u021bia \u03b1 (alfa)<\/strong> \u2013 este format\u0103 din particule alc\u0103tuite din 2 protoni \u0219i 2 neutroni<\/strong>, adic\u0103 nucleul unui atom de heliu. Are o putere de p\u0103trundere redus\u0103 \u0219i poate fi oprit\u0103, de exemplu, de o foaie de h\u00e2rtie.<\/p>\n\n\n\n

      Radia\u021bia \u03b2 (beta)<\/strong> \u2013 este format\u0103, \u00een cazul dezintegr\u0103rii beta minus, din electroni<\/strong> emi\u0219i de nucleu. Are o putere de p\u0103trundere mai mare dec\u00e2t radia\u021bia alfa \u0219i poate fi absorbit\u0103 de un strat de aluminiu.<\/p>\n\n\n\n

      Radia\u021bia \u03b3 (gamma)<\/strong> \u2013 este o radia\u021bie electromagnetic\u0103<\/strong> cu energie mare. Are o putere de p\u0103trundere foarte mare \u0219i necesit\u0103 materiale de protec\u021bie speciale, precum plumbul sau betonul gros.<\/p>\n\n\n\n

      4. Elementele radioactive<\/h3>\n\n\n\n

      Elementele radioactive<\/strong> sunt elemente ale c\u0103ror nuclee atomice sunt instabile \u0219i se dezintegreaz\u0103 spontan.<\/p>\n\n\n\n

      Printre elementele radioactive cunoscute se num\u0103r\u0103:<\/p>\n\n\n\n

        \n
      • uraniul (U);<\/strong><\/li>\n\n\n\n
      • toriul (Th);<\/strong><\/li>\n\n\n\n
      • radiul (Ra);<\/strong><\/li>\n\n\n\n
      • poloniul (Po).<\/strong><\/li>\n<\/ul>\n\n\n\n

        \u00cen urma dezintegr\u0103rii, un element radioactiv se poate transforma \u00eentr-un alt element, p\u00e2n\u0103 c\u00e2nd se ajunge la un nucleu stabil.<\/p>\n\n\n\n

        5. Timpul de \u00eenjum\u0103t\u0103\u021bire<\/h3>\n\n\n\n

        Radioactivitatea nu se desf\u0103\u0219oar\u0103 \u00een acela\u0219i ritm pentru toate elementele. Pentru fiecare radionuclid exist\u0103 o perioad\u0103 caracteristic\u0103 numit\u0103 timp de \u00eenjum\u0103t\u0103\u021bire<\/strong>.<\/p>\n\n\n\n

        Timpul de \u00eenjum\u0103t\u0103\u021bire<\/strong> este intervalul \u00een care num\u0103rul nucleelor radioactive dintr-o prob\u0103 scade la jum\u0103tate.<\/p>\n\n\n\n

        De exemplu, dac\u0103 o prob\u0103 con\u021bine 1000 de nuclee radioactive \u0219i timpul de \u00eenjum\u0103t\u0103\u021bire este de 10 ani, dup\u0103 10 ani vor r\u0103m\u00e2ne, \u00een medie, 500 de nuclee radioactive.<\/p>\n\n\n\n

        6. Utilizarea radioactivit\u0103\u021bii<\/h3>\n\n\n\n

        Radioactivitatea \u0219i radia\u021biile ionizante au numeroase aplica\u021bii practice:<\/p>\n\n\n\n

          \n
        • \u00een medicin\u0103<\/strong>, pentru diagnostic \u0219i tratamentul unor boli;<\/li>\n\n\n\n
        • \u00een industrie<\/strong>, pentru controlul \u0219i verificarea materialelor;<\/li>\n\n\n\n
        • \u00een cercetarea \u0219tiin\u021bific\u0103<\/strong>;<\/li>\n\n\n\n
        • \u00een producerea energiei nucleare<\/strong>;<\/li>\n\n\n\n
        • \u00een arheologie<\/strong>, pentru determinarea v\u00e2rstei unor materiale;<\/li>\n\n\n\n
        • \u00een anumite sisteme de detectare \u0219i m\u0103surare<\/strong>.<\/li>\n<\/ul>\n\n\n\n

          \u00cen acela\u0219i timp, expunerea necontrolat\u0103 la radia\u021bii ionizante poate fi periculoas\u0103 pentru organismele vii. De aceea, utilizarea surselor radioactive se face \u00een condi\u021bii stricte de protec\u021bie \u0219i control.<\/p>\n\n\n\n

          Re\u021bine!<\/h3>\n\n\n\n

          Nucleul atomic<\/strong> este alc\u0103tuit din protoni \u0219i neutroni.
          Radioactivitatea<\/strong> este transformarea spontan\u0103 a unor nuclee instabile, \u00eenso\u021bit\u0103 de emiterea de radia\u021bii.
          Principalele tipuri de radia\u021bii sunt \u03b1, \u03b2 \u0219i \u03b3<\/strong>.
          Elementele radioactive<\/strong> au nuclee instabile \u0219i se pot transforma \u00een alte nuclee.
          Radioactivitatea are aplica\u021bii importante \u00een medicin\u0103, industrie, cercetare \u0219i energetic\u0103, dar necesit\u0103 respectarea strict\u0103 a regulilor de protec\u021bie.<\/p>\n","protected":false},"excerpt":{"rendered":"

          1. Nucleul atomic Atomul este alc\u0103tuit dintr-un nucleu atomic \u0219i electroni care se afl\u0103 \u00een jurul acestuia. Nucleul este foarte mic \u00een compara\u021bie cu dimensiunea atomului, dar con\u021bine aproape \u00eentreaga […]<\/p>\n","protected":false},"author":1,"featured_media":2906,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[18,10],"tags":[],"_links":{"self":[{"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/posts\/2904"}],"collection":[{"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cedra.academy\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2904"}],"version-history":[{"count":1,"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/posts\/2904\/revisions"}],"predecessor-version":[{"id":2908,"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/posts\/2904\/revisions\/2908"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cedra.academy\/index.php?rest_route=\/wp\/v2\/media\/2906"}],"wp:attachment":[{"href":"https:\/\/cedra.academy\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2904"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cedra.academy\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2904"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cedra.academy\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2904"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}