THE NUCLEUS OF THE ATOM
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Transcript of THE NUCLEUS OF THE ATOM
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THE NUCLEUS OF THE ATOM
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• Components of the Atomic Nucleus– Protons– Neutrons and Isotopes– Radioactivity
• Development of Nuclear Weapons• Nuclear Energy• Particle Physics– Standard Model– Four Fundamental Froces
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Potential Energy of any Body of Mass
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The Proton
• Rest Mass =1.007276466812awu
• Average Lifetime years• Discovered, described,
and named by Ernest Rutherford over a three-year period (1917-1920)
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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
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The Neutron
• Rest Mass =1.0086649160043awu• Average Lifetime =881.515 sec
Chadwick’s experimental design
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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.
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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
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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) Salomea Sklodowska-Curie;
1867-1934; Poland and FrancePierre Curie; 1859-1909; France
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Types of Radiation
Paper
Aluminum
LeadM
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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
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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)
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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
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Half-Life
• Probabilistic nature• Exponential decay• Rutherford suggested it
as a way to date minerals.
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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
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Decay Chains
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Controlled Nuclear Fission
Otto Hahn1879-1968; Germany
Friedrich Wilhelm ‘Fritz’ Strassman1902-1980; Germany
Lise Meitner1878-1968; Austria, GermanySweden, UK
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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
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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
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Letter to FDR
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The Manhattan Project
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Little Boy, The Uranium Bomb
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Fat Man, The Plutonium Bomb
At Trinity Test SiteLeft: J. Robert Oppenheimer, scientific leader of Los AlamosRight: Gen. Leslie Groves
Plutonium bred from U-238 in reactors at Hanford, WA
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The Only Uses of Atomic Devices in War
Little Boy at Hiroshima, 6 August 1945Yield: 16 ktCasualties: >90,000 dead
Fat Man at Nagasaki, 9 August 1945Yield: 21 ktCasualties: >60,000 dead
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The Cold War and Destruction Unlimited
Edward Teller (1908-2003)Hungary and USA
10.4mtMIKE1952
W-88WarheadFor Trident II missiles475kt
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Nuclear Energy
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Accidents
TMI unit 2 28 March 1979 Chernobyl 26 April 1986
Fukushima-1 11 March 2011
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Accelerators
Tevatron at Fermilab, near Chicago
Large Hadron Collider, CERN
Appearance of the spray of subatomic particles from a high energy collision
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The Standard Model of Particle Physics
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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.
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Strong Nuclear Force
• ~100X stronger than EM force
• Binds hadrons (protons & neutrons) in nucleus
• Binds quarks to form hadrons
u = +2/3d = -1/3
Gauge particle is gluon
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Weak Nuclear Force
W & Z bosons ~100 times as massive as a proton
Reprise β-decay with quarks and W- bosonResults of weak nuclear interactions
• Radioactive decay• Beta decay• Burning of sun• Initiating the process of hydrogen fusion in
stars.• Production of deuterium• Formation of other heavy nuclei• Radiocarbon dating
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Antimatter
• Every particle has an anti-particle (e.g. electron vs. positron)
• Electron-positron annihilation yields gamma radiation
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