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What is Radioactivity?

What is Radioactivity?. BNEN Nuclear Energy: Intro William D’haeseleer. Chemical elements. Periodic Table (Mendeleev). Chemical elements. Periodic Table (Mendeleev) Focuses on the electrons in atoms. Chemical elements. Periodic Table (Mendeleev) Focuses on the electrons in atoms.

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What is Radioactivity?

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  1. What is Radioactivity? BNEN Nuclear Energy: Intro William D’haeseleer BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  2. Chemical elements • Periodic Table (Mendeleev) BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  3. BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  4. Chemical elements • Periodic Table (Mendeleev) • Focuses on the electrons in atoms BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  5. Chemical elements • Periodic Table (Mendeleev) • Focuses on the electrons in atoms BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  6. Chemical elements • Periodic Table (Mendeleev) • Focuses on the electrons in atoms BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  7. Chemical elements • Periodic Table (Mendeleev) • Focuses on the electrons in atoms BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  8. Atoms vs Nuclei & Electron Cloud (neutral) atom = nucleus + Z electrons ion = ionized atom nucleus = Z protons + N neutrons = A nucleons Matter is basically “empty space”, but electrons move at very high speed BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  9. Exited states in atoms Stationary states Hydrogen Mercury (simplified) BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  10. Exited states in atoms Transitions in eV range Emitted e.m. radiation = UV or X rays BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013 1 eV = 1.6 10-19 Joule

  11. Transitions btwn shells in atoms BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  12. Exited states in nuclei Nuclei vibrate & rotate BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  13. Exited states in nuclei Nuclei vibrate & rotate BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  14. Exited states in nuclei Stationary states Transitions in MeV range Emitted e.m. radiation = Gamma rays BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  15. Electromagnetic spectrum Gamma rays Common e.m. waves: Radio TV Micro-wave I.R. (heat) visible UV & X rays BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  16. Elements vs Isotopes • Chemical elements characterized by Z • Number of protons = Z • Number of electrons = Z • If same Z but different N, particles called isotopes of chemical element • E.g., Hydrogen has three isotopes • Sometimes “isotope” used as generic name of all nuclei/atoms with all kinds of Z & A. BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  17. Some light Isotopes proton neutron BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  18. Rank all stable isotopes in (N,Z) plot Every stable isotope represented by a black dot 208Pb last stable nucleus BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  19. Chart of Nuclides About 1400 isotopes known About 280 stable About 1220 unstable BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  20. Chart of Nuclides Too many protons Too many neutrons BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  21. Chart of Nuclides BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  22. Z Chart of Nuclides 208Pb last stable nucleus N BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  23. Z Chart of Nuclides 61Pm 43Tc N BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  24. Z Chart of Nuclides Too many protons Too many neutrons N BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  25. Radioactive decay Beta- decay when too many neutrons: neutron proton + electron(+ anti neutrino) A remains same Z  Z+1& N N-1 BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  26. Radioactive decay Beta+ decay when too many protons: proton neutron + positron(+ neutrino) A remains same Z  Z-1& N N+1 BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  27. Radioactive decay p n e+ before after BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  28. Z Chart of Nuclides Heavy unstable isotopes N BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  29. Z Chart of Nuclides Heavy unstable isotopes Wish to move downward quickly N BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  30. Radioactive decay Emission two protons & two neutrons A  A – 4 & Z  Z – 2 N  N - 2 BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  31. Radioactive decay BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  32. Summary radioactive decay Alpha decay Beta decay beta- decay beta+ decay Energetic alpha Energetic electron Energetic positron BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  33. Alpha energies • Well defined energies of emitted alpha particles upon transition • Typically ~ 4-10 MeV BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  34. Beta energies • Energy variable (because neutrino) Beta min = electronBeta plus = positron BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  35. Beta energies Emitted energies vary considerably dependent on isotope BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  36. And Gamma rays? BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  37. Gamma decay • Gamma decay typically follows beta decay • Beta decay often to excited state of daughter • Excited daughter then decays very quickly to lower state BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  38. Gamma decay (after beta decay) BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  39. Beta - Gamma decay E.g., beta min decay BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  40. Alpha - Beta - Gamma decay 212Bi has all three decay modes BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  41. Alpha - Beta - Gamma decay BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  42. When radioactive decay? Start from N° radioactive isotopes λ= desintegration constant = probability for decay per second BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  43. When radioactive decay? Half life = time that half of the isotopes has decayed Average life time isotope BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  44. When radioactive decay? Activity = number of disintegrations per second = Becquerel= Bq= [1/s] Old unit = Curie = Ci ; 1 Ci = 37 GBq BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  45. When radioactive decay? BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  46. Radioactive chains • Very often daughter also unstable •  Radioactive chains N1 λ1 N2 λ2 N3 BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  47. Natural Radioactivity • Many unstable isotopes exist in nature, and originate from nature • Cosmogenic isotopes • Primordial isotopes • Very long lived lighter than Pb • Natural radioactive chains 238U 235U 232Th • Transuranic elements & Np decay series BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  48. Natural Radioactivity • Many unstable isotopes exist in nature, and originate from nature • Cosmogenic isotopes • Primordial isotopes • Very long lived lighter than Pb • Natural radioactive chains 238U 235U 232Th • Transuranic elements & Np decay series BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  49. Cosmogenic isotopes • Interaction of cosmic radiation produces protons & neutrons which interact with with nuclei from atmosphere • Produce radioactive isotopes • Typical examples: BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

  50. Cosmogenic Example C-14 BNEN – Nuclear Energy Intro W. D’haeseleer 2012-2013

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