The discovery of how to release nuclear energy was arguably the most important human discovery since

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• The discovery of how to release nuclear energy
  was arguably the most important human discovery
  since fire - reason enough to preserve its
  remarkable history.
• - Pulitzer-prize winner Richard Rhodes

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Fallout from Trinity
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Oppenheimer, after Trinity Test(July 16, 1945)

• We waited until the blast had passed, walked
  out of the shelter and then it was extremely
  solemn. We knew the world would not be the same.
  A few people laughed, a few people cried, most
  people were silent. I remembered the line from
  the Hindu scripture, the Bhagavad-Gita. Vishnu is
  trying to persuade the Prince that he should do
  his duty and to impress him takes on his
  multi-armed form and says, Now, I am become
  Death, the destroyer of worlds. I suppose we all
  thought that one way or another.
• - J. Robert Oppenheimer

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• "My God, what have we done?"
• - Robert Lewis, the co-pilot of the Enola Gay

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Nuclear Status
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Atomic Physics

• Atom from Greek atomos
• Components of atom
• Nucleons protons and neutrons
• Compose nucleus
• Electrons surround nucleus
• Scale
• Atomic radius 1 ? 10-10 m
• Nuclear radius 1/10000 ? 10-14 m

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Atomic Physics

• Protons
• Number of protons Z
• Positive electrical charge
• Atomic number
• Determines element
• Neutrons
• Number of neutrons N
• Neutral (no) electrical charge
• Same Z, different N isotope
• ZN A number of nucleons
• Atomic Mass
• Electrons
• Negative electrical charge
• mass of electron 1/2000 x mass of proto
• mp mn 2000me

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Atomic Physics
Representing elements
Examples of different elements
Examples of different isotopes
0.72 99.28
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Atomic Physics
Isotopes can either stable, or unstable (or
radioactive)
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History of Atomic Physics

• 1896 Henri Becquerel discovers radioactivity
  the spontaneous emission of radiation
• 1897 J.J. Thomson discovers cathode rays are
  electrons develops plum pudding model for atom

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Radioactive Decay

• Radioactivity
• The spontaneous disintegration of atomic nuclei
  the result of atom trying to reach a more stable
  nuclear configuration
• Made scientists change their ideas about the
  structure of the atom.
• Can be achieved via three methods
• Alpha decay Nucleus emits a helium nucleus
• Beta decay Nucleus can change one of its
  neutrons into a proton with the simultaneous
  emission of an electron
• Gamma decay The release of high energy photons
  or gamma rays often associated with the
  spontaneous fission (splitting) of nucleus into
  two fragments.

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Radioactive Decay

• Each radioactive substance has a characteristic
  decay period or half-life the interval of
  time required for one-half of the atomic nuclei
  of a radioactive sample to decay. Half-lives can
  range from millions of years to less than a
  millisecond.
• Residual radioactivity After radioactive decay,
  the new atom can be left in another radioactive
  form the atom will decay again as it attempts
  to reach a stable nuclear state.