Great Ideas in Science: Lecture 7 – Nuclear Reactions

1. Great Ideas in Science:Lecture 7 – Nuclear Reactions Professor Robert Hazen UNIV 301 Great Idea: Nuclear energy arises from the conversion of mass into energy.

2. Nuclear Reactions • Key Idea: Nuclear reactions result from the rearrangement of an atom’s protons and neutrons (i.e. the nucleus) • Key Words: • Proton • Neutron • Nucleus • Isotope • Radioactivity • Nuclear Fission • Nuclear Fusion

3. The Building Blocks of Matter Of what is matter made? • Atoms • Nuclei and electrons • Quarks

4. Key Words About Atoms • Atom: Any object with a nucleus and electrons • Element: An atom with a known number of protons (the atomic number) • Ion: An electronically-charged atom with a different number of protons (+) and electrons (-) • Isotope: An element with a known number of neutrons

5. The Structure of the Atom Electrons in shells (energy levels) • Negatively charged • Shift during chemical reactions

6. The Structure of the Atom Electrons in shells (energy levels) • Negatively charged • Shift during chemical reactions Central dense nucleus • Composed of protons and neutrons • Positively charged • Nucleus - Stays put in chemical reactions

7. Isotopes: Hydrogen & Carbon • H-1 – 1 proton • H-2 – 1 p & 1 neutron (Deuterium) • H-3 – 1 p & 2 n (Tritium) • C-12 – 6p & 6n • C-13 – 6p & 7n • C-14 – 6p & 8n (radioactive) • For any given element the number of protons is fixed

8. Four Fates of Isotopes • An isotope may be stable • An isotope may be radioactive • An isotope may be split apart by fission • An isotope may combine with another by fusion

9. Chart of the Isotopes (Z vs. N)

10. Stable Isotopes • 99.999+% of all the atoms around us • Examples are carbon-12 and carbon-13 • Different isotopes don’t affect chemical reactions. • Used in scientific research to track chemical reactions (2 ways) • As tracers • Fractionation

11. Radioactivity or Radioactive Decay (three kinds) The spontaneous emission of an energetic particle by a nucleus • Alpha radiation • Beta radiation • Gamma radiation

12. Most Kinds of Isotopes are Radioactive STABLE RADIOACTIVE

13. Alpha Radiation • Atom spontaneously loses 2 protons and 2 neutrons (= a Helium-4 nucleus)

14. Alpha Radiation • Atom spontaneously loses 2 protons and 2 neutrons (= a Helium-4 nucleus) • Uranium-238  Thorium-234 + 2n + 2p

15. Beta Radiation • One neutron spontaneously becomes a proton plus an electron • Thorium-234  Proactinium-234

16. Gamma Radiation • Atom spontaneously emits a gamma ray (electromagnetic radiation) • Uranium-238*  Uranium-238 + γ

17. Gamma Radiation • Atom spontaneously emits a gamma ray (electromagnetic radiation) • Uranium-238*  Thorium 234 + γ

18. SUMMARY: The Three Kinds of Radioactive Decay • Alpha Decay • Release of αparticle with 2 protons and 2 neutrons • Beta Decay • Neutron becomes a proton • Emission of electron (β-ray) • Gamma Radiation • Electromagnetic radiation

19. Radioactivity and Health Ionization • Stripping off electrons Long-term effects • Cancer • Birth defects

20. Half-Life • The average time for decay of ½ batch of radioactive isotopes • Wide range of half-lives

21. Radiometric Dating • Know half-life of isotope • Know how much was there • Measure what’s left Carbon-14: Half-life = 5730 years

22. Radiometric Dating Applications to geology • Need longer half-lives • Uranium, potassium

23. Radioactive Decay Chain (radon)

24. Radioactive Decay Chain (radon)

25. Radioactive Decay Chain (radon)

26. Radioactive Decay Chain (radon)

27. Radioactive Decay Chain (radon)

28. Radioactive Decay Chain (radon)

29. Radioactive Decay Chain (radon)

30. Radioactive Decay Chain (radon)

31. Radioactive Decay Chain (radon)

32. Radioactive Decay Chain (radon)

33. Radioactive Decay Chain (radon)

34. Radioactive Decay Chain (radon)

35. Radioactive Decay Chain (radon)

36. Four Fates of Isotopes • An isotope may be stable • An isotope may be radioactive • An isotope may be split apart by fission • An isotope may combine with another by fusion

37. Nuclear Fission (Splitting) • Fission = Splitting of nucleus • A nuclear reactor converts mass to energy

38. Nuclear Fission (Splitting)

39. Nuclear Fission – The Atom Bomb Hiroshima – August 6, 1945

40. Nuclear Fission – The Atom Bomb

41. Yucca Mountain, Nevada (NIMBY)

42. Yucca Mountain, Nevada (NIMBY)

43. Four Fates of Isotopes • An isotope may be stable • An isotope may be radioactive • An isotope may be split apart by fission • An isotope may combine with another by fusion

44. Nuclear Fusion (Fusing) • Hydrogen atoms combine to form helium • Some mass is converted into energy

45. Nuclear Fusion – Hydrogen Bomb

46. Nuclear Fusion – Hydrogen Bomb

47. Stars are Giant Fusion Reactors http://www.earth.northwestern.edu/people/seth/107/Solar/Image12.gif

48. Fates of Stars

49. Benefits of Isotopes • Stable Isotopes • Medical Research • Environmental Tracers • Radioactive Isotopes • Medical diagnosis • Cancer treatments • Environmental tracers • Age Determination • Nuclear fission • Power generation • Nuclear Fusion • The Sun