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 Idea: Nuclear reactions result from the rearrangement of an atom’s protons and neutrons (i.e. the nucleus) Key Words: Key Words: ProtonProton NeutronNeutron NucleusNucleus IsotopeIsotope RadioactivityRadioactivity Nuclear FissionNuclear Fission Nuclear FusionNuclear Fusion

3. The Building Blocks of Matter Of what is matter made? AtomsAtoms Nuclei and electronsNuclei and electrons QuarksQuarks

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

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

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

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

8. Four Fates of Isotopes An isotope may be stable An isotope may be stable An isotope may be radioactive An isotope may be radioactive An isotope may be split apart by fission An isotope may be split apart by fission An isotope may combine with another by fusion 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 99.999+% of all the atoms around us Examples are carbon-12 and carbon-13 Examples are carbon-12 and carbon-13 Different isotopes don’t affect chemical reactions. Different isotopes don’t affect chemical reactions. Used in scientific research to track chemical reactions (2 ways) Used in scientific research to track chemical reactions (2 ways) As tracersAs tracers FractionationFractionation

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

12. Most Kinds of Isotopes are Radioactive STABLE RADIOACTIVE

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

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

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

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

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

19. Radioactivity and Health Ionization Stripping off electronsStripping off electrons Long-term effects CancerCancer Birth defectsBirth defects

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

21. Radiometric Dating 1.Know half-life of isotope 2.Know how much was there 3.Measure what’s left Carbon-14: Half-life = 5730 years Carbon-14: Half-life = 5730 years

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

23. Radioactive Decay Chain (radon)

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

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

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

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

45. 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 Stable Isotopes Medical ResearchMedical Research Environmental TracersEnvironmental Tracers Radioactive Isotopes Radioactive Isotopes Medical diagnosisMedical diagnosis Cancer treatmentsCancer treatments Environmental tracersEnvironmental tracers Age DeterminationAge Determination Nuclear fission Nuclear fission Power generationPower generation Nuclear Fusion Nuclear Fusion The SunThe Sun