seriile radioactive
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SERIILE RADIOACTIVE
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Antoine Henri Becquerel, Marie Sklodowska Curie si Pierre Curie
Premiul Nobel (1903) “ca apreciere pentru serviciile extraordinare aduse prin
descoperirea radioactivitatii spontane si implicatiile asupra dezvoltarii fizicii”
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Radioactivitatea este proprietatea unor nuclee de a se dezintegra spontan prin emisia de radiatii.
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Dezintegrarea radioactiva este procesul spontan prin care nucleul
instabil se transforma intr-un nucleu mai stabil, caracterizat de energie
mai mica, in urma emisiilor de radiatii.
Atomul isi schimba pozitia in sistemul periodic al elementelor.
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Dezintegrarea α
Dezintegrarea β-
Dezintegrarea β+
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Legea generala a dezintegrarii radioactive permite calcularea
numarului N de nuclee radioactive ramase nedezintegrate la
momentul de timp t fata de momentul initial (t0=0), cand au fost N0 nuclee nedezintegrate.
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Timpul de injumatatire reprezinta perioada dupa care numarul de
nuclee radioactive se reduce, prin dezintegrare, la jumatate din
valoarea sa initiala.
T1/2 = ln 2 / λ
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Radioactivitatea este practic
constanta pentru izotopii radioactivi care au timpul de injumatatire foarte
mare de ordinul miilor de ani.
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In anul 1934, Frédéric si Irène
Joliot-Curieau obtinut pentru
prima data radioactivitatea
artificiala a unei foite de aluminiu iradiata cu particule α, emise in mod natural de o
sursa radioactiva.
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Nucleele radioactive obtinute prin dezintegrari formeaza serii
radioactive: seria Thorului, a Uraniului sau a Actiniuliu.
Radioactivitatea naturala este caracteristica nucleelor cu A>200 si
mai rar intalnita la celelalte.
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În stare naturala, uraniul se gaseste sub forma preponderent a izotopului uraniu 238, respectiv a izotopilor uraniu 235 si a unei cantitati foarte reduse de uraniu
234.
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Proiect realizat de
Caiali Arzzu-Ellis
Clasa a XII-a A