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THE NUCLEUS OF THE ATOM

THE NUCLEUS OF THE ATOM. Potential Energy of any Body of Mass. The Proton. Rest Mass =1.007276466812awu Average Lifetime years Discovered, described, and named by Ernest Rutherford over a three-year period (1917-1920). James Chadwick. Student of Rutherford

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THE NUCLEUS OF THE ATOM

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  1. THE NUCLEUS OF THE ATOM

  2. Potential Energy of any Body of Mass

  3. The Proton • Rest Mass =1.007276466812awu • Average Lifetime years • Discovered, described, and named by Ernest Rutherford over a three-year period (1917-1920)

  4. James Chadwick • Student of Rutherford • Designed an experiment with Polonium and Beryllium target. Detected an uncharged form of radiation that had a mass approximately equal to the proton. • He called it the neutron. 1891-1974; Britain

  5. The Neutron • Rest Mass =1.0086649160043awu • Average Lifetime =881.515 sec Chadwick’s experimental design

  6. Isotopes • Following the discovery of neutrons, the disagreement between atomic number and atomic mass for the elements became clear. • Also, the disagreement between different forms of the same element could be explained.

  7. Antoine Henri Becquerel • Discovered penetrating radiation by uranium salts that exposed photographic plates in the absence of visible light. • Reported in 1896. 1852-1908; France

  8. Marie & Pierre Curie Following report of invisible radiation, Pierre and Marie worked on characterizing the radiation and finding other radioactive elements (e.g. Radium). Maria (Marie) SalomeaSklodowska-Curie; 1867-1934; Poland and France Pierre Curie; 1859-1909; France

  9. Types of Radiation Paper Aluminum Lead M

  10. Alpha Radiation (α-decay) • Discovered and named by Rutherford • Reduces the atomic number by 2 and atomic mass by 4 • Equivalent to a helium nucleus

  11. Beta Radiation (β-decay) • Discovered by Becquerel and named by Rutherford • Neutron decays to a proton, an electron, an electron neutrino • Initiated in the nucleus by neutron spontaneously changing to proton (mediated by the weak nuclear force)

  12. Gamma Radiation (γ-decay) • Discovered by Villard and named by Rutherford • Type of photon – high energy x-ray with frequency >1019 Hz • Potassium-40 good source • γ-decay in association with α and/or β decay

  13. Half-Life • Probabilistic nature • Exponential decay • Rutherford suggested it as a way to date minerals.

  14. Radiometric Dating Based on two decay sequences: 238U to 206Pb (half-life 700 million years) 235U to 207Pb (half-life 4.5 billion years) Usually taken from very stable zircon crystals

  15. Decay Chains

  16. Controlled Nuclear Fission 1902-1980; Germany 1879-1968; Germany

  17. Leo Szilard Tuesday, September 12, 1933. The stoplight changed to green. Szilárd stepped off the curb. As he crossed the street time cracked open before him and he saw a way to the future, death into the world and all our woes, the shape of things to come. (Rhodes 1986) 1898-1964; Hungary and USA

  18. Enrico Fermi • Began to bombard elements with neutrons and transmutated them into different elements • In USA built first reactor to create a sustained nuclear reaction • Developed theory of β-decay 1901-1954; Italy and USA Pile-1; University of Chicago 2 December 1942

  19. Letter to FDR

  20. The Manhattan Project

  21. Little Boy, The Uranium Bomb

  22. Fat Man, The Plutonium Bomb Plutonium bred from U-238 in reactors at Hanford, WA At Trinity Test Site Left: J. Robert Oppenheimer, scientific leader of Los Alamos Right: Gen. Leslie Groves

  23. The Only Uses of Atomic Devices in War Little Boy at Hiroshima, 6 August 1945 Yield: 16 kt Casualties: >90,000 dead Fat Man at Nagasaki, 9 August 1945 Yield: 21 kt Casualties: >60,000 dead

  24. The Cold War and Destruction Unlimited 10.4mt MIKE 1952 Edward Teller (1908-2003) Hungary and USA W-88 Warhead For Trident II missiles 475kt

  25. Nuclear Energy

  26. Accidents TMI unit 2 28 March 1979 Chernobyl 26 April 1986 Fukushima-1 11 March 2011

  27. Accelerators Tevatron at Fermilab, near Chicago Large Hadron Collider, CERN Appearance of the spray of subatomic particles from a high energy collision

  28. The Standard Model of Particle Physics

  29. The Four Fundamental Forces of Nature • Strong Nuclear Force: short range but very strong in attracting quarks (exchange of gluons changes color) within hadrons (e.g. protons and neutrons) • Weak Nuclear Force: short range and weaker than all forces except gravity. Exchange of W and Z bosons between quarks changes their flavor (e.g. U or D). • Electromagnetic Force: long distance and obeys inverse square law. Photons carry force which is exchanged between leptons. • Gravitational Force: long distance and obeys inverse square law. Gravitons attract all particles that have mass.

  30. Strong Nuclear Force u = +2/3 d = -1/3

  31. Weak Nuclear Force

  32. Antimatter • Every particle has an anti-particle (e.g. electron vs. positron) • Electron-positron annihilation yields gamma radiation

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