Physical Science

1. Physical Science Nuclear Physics Slides subject to change

2. Atoms • Each chemical element is composed of tiny, indivisible particles called atoms, which are identical for that element but different (masses and chemical properties) from atoms of other elements. Consists of negatively charged electrons and a small positively charged nucleus. Planetary Model

3. Nucleus • Nucleus consists of positively charged protons and, electrically neutral neutrons. • Protons and neutrons are collectively called nucleons. • Relative size - a marble in a football stadium.

4. Labels • Each element is assigned a chemical symbol. This symbol usually originates from its name or its Latin name. • H = Hydrogen • He = Helium • C = Carbon • Number of protons Z is the atomic number. All the atoms of an element have the same atomic number.

6. X A Z U 238 92 Mass Number • Number of protons is the atomic number, Z. • Number of protons plus neutrons is the mass number, A. Mass Number Element Atomic Number, or number of protons Uranium In General

7. U 238 92 Details on a Uranium Nucleus • How many protons? 92 • How many neutrons? 238 – 92 = 146 • Mass number? 238 Uranium

8. Background on Uranium • Discovered in 1789, named after planet Uranus discovered 8 years earlier. • Common element in Earth’s crust. One of the radioactive elements responsible for molten layer between Earth’s crust and core (more uranium in Earth’s crust than silver). • First radioactive material discovered in 1896.

9. U U 238 235 92 92 Isotopes • Forms of an element with different numbers of neutrons. • Have same chemical properties, may have different physical properties. Uranium 235 rare in nature but needed for power/weapons, 0.7% Uranium 238 plentiful in nature, 99.3%

11. Strong Nuclear Force • Overcomes Coulomb repulsion force. • Short range, only nearest neighbor nucleons involved. • Large nucleus becomes very unstable. • When over 83 protons, nucleus is subject to spontaneous disintegration. Nucleus of U-235: protons in red, neutrons in grey.

12. Radioactivity • Some nuclei spontaneously decay. • Discovered in 1896 by Henri Becquerel studying fluorescence and phosphorescence, and working with uranium salts and photographic plates. • The spontaneous process of nuclei undergoing a change by emitting particles or rays is called radioactive decay.

13. An Alpha Decay Process Alpha particles: He nuclei (2 protons, 2 neutrons) Mass numbers and atomic numbers add up and match. Uranium decays to thorium. + U Th He 238 234 4 + 92 90 2 +

14. Beta Decay Beta particles: Electrons. A neutron decays in the nucleus to a proton and a neutron. Atomic mass and atomic numbers add up and match. Example is Cobalt-60. Decays to an unstable nickel atom. e 0 + Ni* 60 -1 28 Co 60 27

15. Gamma Decay Gamma rays consist of high energy photons with energies above about 100,000 eV (>1019 Hz). Due high energy content, gamma rays can cause serious damage when absorbed by living cells (photons strike DNA). Ni γ 60 + 27 Ni* 60 27

16. Uranium Pitchblende ore contains uranium Commercial Uranium : “Yellow Cake” Lisbon Valley, UT

17. 226 Ra 88 Radium • Discovered by Pierre and Marie Curie in 1898. Discovered mixed with uranium. Shared 1903 Nobel Prize with Henri Becquerel. • Million times more radioactive than uranium. Radium dust mixed with water and glue used to make radioluminescent paint during 1920’s: watch dials, instruments.

18. Early Application • When a radium atom decays, one of the particles it ejects (an alpha particle) hits a phosphor molecule in the surrounding paint that the manufacturer used to paint the watch dial's numbers.  • Then the phosphor glows a faint blue-green light. The radium, however, does not glow; only the phosphor glows.

19. Radium Girls U.S. Radium CorporationOrange, NJ, ca.1920

20. Radium Girls • The employees hired to paint the dials were mostly young women. Paint was applied with a small brush. • The women "pointed" the brushes on their tongues between applications, and ingested a small quantity of radium each time. • “But everyone knew the stuff was harmless. The women even painted their nails and their teeth to surprise their boyfriends when the lights went out.

21. Danger to Radium Girls • Radium is chemically similar to calcium, and is therefore a “bone seeker.” It emits alpha-particles. • 226Ra that accumulated in the bone marrow irradiated nearby tissue, and produced bone cancer and other genetic damage. • Curie herself died of radium poisoning in 1934. • The right of individual workers to sue for damages from corporations due to labor abuse was established as a result of the Radium Girls case. See article.

22. Products of Radioactivity • Decay in three common ways: • Emit alpha particles: Helium nuclei (2 protons, 2 neutrons). • Emit beta particles: Electrons. • Emit gammarays: High energy photons. α β γ

23. Half-Life • Half-life is the time it takes for half of the nuclei of a sample to decay. • Radioactive isotopes have characteristic half-lives. 50 g of other atoms 100 g of X 75 g of other atoms First half life Second half life 50 g of X 25 g of X

24. Example Half-Lives α decay to 222Rn (radon) • After cigarettes, radon is the second leading cause of lung cancer. − EPA

25. Quantity of Radioisotope 100 Amount of substance, in % 50 25 0 Years, in half-lives

27. Lise Meitner Otto Hahn Ba 142 n U 1 235 n Kr 1 92 56 0 92 0 36 Fission • Large unstable nucleus splits into two intermediate-size nuclei, emits neutrons. • Example: Uranium-235 fission. Bombard with one low-energy “thermal” neutron (Otto Hahn and Lise Meitner experiment). +2 + + - one of several U-235 decay processes

28. U-235 Fission 142

29. Missing Mass

30. How Masses Add Up • Resulting masses are lighter. • Where did the mass go? • Lise Meitner proposed that it goes into energy from Einstein’s equation E = mc2.

31. Summary • One neutron absorbed by U-235, momentarily becomes U-236, unstable, and splits into smaller atoms with tremendous kinetic energy (Coulomb repulsion) (~200 MeV) plus a few neutrons. • Visualize with Niels Bohr water drop model.

32. Fission

33. Critical Mass • When the process is self-sustaining, the sample has a critical mass. • For every 2 or 3 neutrons released, at least one must strike another uranium nucleus. • If less than 1, then the reaction will die out. • Greater than one it will grow unless controlled (chain reaction).

34. Controlled Reaction • Slow Fission Down! • A control rod (neutron-absorbing element boron or cadmium) absorbs a large number of neutrons in the reaction. • Speed Fission Up! • Fission works best with slow neutrons. • Need a moderator (e.g., graphite, water) to slow down high-speed neutrons that are created.

35. WarningsAug 2, 1939 Einstein to FDR. Possibility that Nazis were developing an atomic bomb.

36. First Controlled Fission • December 2, 1942. • Enrico Fermi, University of Chicago. • Natural uranium, cadmium control rods. • 315 tons of graphite used as a moderator to slow down the neutrons.

37. Manhattan Project • In an atomic bomb, a mass of fissile material greater than the critical mass must be assembled instantaneously. • Held together for about a millionth of a second to permit the chain reaction to propagate before the bomb explodes

38. Manhattan Project

39. Hiroshima • “Little Boy,” dropped on Hiroshima, Japan, August 8, 1945. • Explodes 1,900 feet above city. • 140,000 people die immediately. • Equivalent to 13 kilotons of dynamite. • Used 60 kg (132 lbs) of U-235. • August 15, 1945, Japan announces surrender, ending WWII. (Germany had surrendered May 7, 1945)

40. Hiroshima

41. Nuclear Tests in Nevada • Interview

42. Controlled Nuclear Power Three-Mile Island, Middletown, PA

43. Nuclear Power Plant Light and Heat Energy Mechanical Energy Electrical Energy Nuclear Energy Thermal Energy

44. Nuclear Fuel Life Cycle Uranium enrichment centrifuges Enrichment Ore Processing Fuel Production Power Reactor Uranium Mine Used Fuel Disposal Cameco Corp.'s uranium mine in northern Saskatchewan Road transport of spent fuel in Japan

45. Nuclear Waste Percent of Radioactive Waste Worldwide Percent of Total Radioactivity

46. High-Level Waste • Thermally hot, highly radioactive, and potentially harmful used nuclear reactor fuel. • Converted into granules and mixed with molten glass and stored. Licensees must safely store this fuel at their reactors. • Disposal of high-level radioactive waste was defined by the Nuclear Waste Policy Act of 1982.

47. High-Level Waste • Nuclear Waste Policy Act of 1982: Dispose high-level waste at Yucca Mountain, Nevada. • 80 miles northwest of Las Vegas, NV. • No official date for opening the $12 billion facility. • 3/7/09 Obama proposed budget closed the facility. Satisfies Harry Reid (D-Nev). • What to do with existing 57,000 tons of highly toxic waste at 121 above-ground sites? • Existing plants create 2,000 tons each year. • DOE study underway to find an alternative.

48. Low-Level Waste • Slightly radioactive. • Includes things like protective clothing, laboratory equipment, paper towels, gloves, etc. Hospital, industry waste. • Compacted using a high force compactor. Bury in shallow pits.

49. WIPP • Waste Isolation Pilot Project (WIPP), Carlsbad, NM, is the nation’s only permanent, deep geologic repository for nuclear waste. • Storage for radioactive drums with the plutonium-laden detritus of America’s nuclear weapons program. • 3,000-ft salt layer. Forbes, 2/13/12 p. 91.

50. n Clean Nuclear Process? • Are there heavier elements that can be fused into a lighter element (so missing mass goes off as E=mc2 energy)? • Fusion energy would be “clean.” No radioactive waste products.