1. Great Ideas in Science: Lecture 7 – Nuclear Reactions
Professor Robert Hazen
PROV 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. A Hierarchy of Scientific Ideas
Fact (a confirmed observation)
Hypothesis (an educated guess)
Law (a predictive mathematical description of nature)
Theory (a well established explanation of nature)

5. 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

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

7. 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

8. 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

9. 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

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

11. 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

12. 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

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

14. Most Kinds of Isotopes are Radioactive
STABLE
RADIOACTIVE

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

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

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

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

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

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

21. Radioactivity and Health
Ionization
Stripping off electrons
Long-term effects
Cancer
Birth defects
Alpha
Beta
Gamma

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

23. Radiometric Dating Measure the half-life of the isotope.
Estimate how much was there at first.
Measure what’s left now.
Carbon-14: Half-life = 5730 years

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

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. Radioactive Decay Chain (radon)

37. Radioactive Decay Chain (radon)

38. 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

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

40. Nuclear Fission (Splitting)

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

42. Nuclear Fission – The Atom Bomb

43. Yucca Mountain, Nevada (NIMBY)

44. Yucca Mountain, Nevada (NIMBY)

45. 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

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

47. Nuclear Fusion – Hydrogen Bomb

48. Nuclear Fusion – Hydrogen Bomb

49. Stars are Giant Fusion Reactors

50. Fates of Stars

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