Quick review

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Quick review

• Atom constituents
• Nucleons
• Why nuclear more powerful?
• Element
• Isotope
• .
• Atomic number atomic mass
• Atomic

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Fundamental Forces
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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.

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Alpha Decay

• Discovered in 1899 by Sir Ernest Rutherford
• A positively charged particle, identical to the
  nucleus of helium 4, is emitted spontaneously.
• Usually occurs in heavy nuclei such as uranium
  or plutonium
• A major part of the radioactive fallout from a
  nuclear explosion
• Relatively more massive than other forms of
  radioactive decay can be stopped by a sheet of
  paper and cannot penetrate human skin.

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Beta Decay

• Discovered by Rutherford in 1899
• Occurs when an atom has either too many protons
  or too many neutrons in its nucleus
• Two types of beta decay can occur
• Beta particles travel at nearly the speed of
  light
• Can generally be stopped by 1-2 inches of wood,
  or thin sheet of aluminum foil

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Gamma Decay

• Discovered in 1898 by Paul Villard
• A type of electromagnetic radiation that results
  from a redistribution of electric charge within a
  nucleus
• A high energy photon (Essentially a very
  energetic X ray)
• Often accompanies alpha or beta radiation, as a
  nucleus emitting those particles may be left in
  an excited (higher-energy) state.
• More penetrating than either alpha or beta
  radiation, but less ionizing
• Can generally be stopped by several inches of
  lead
• Gamma rays from nuclear fallout would probably
  cause the largest number of casualties in the
  event of the use of nuclear weapons in a nuclear
  war produce damage such as burns, cancer, and
  genetic mutations.

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History of Atomic Physics

• 1911 Ernest J. Rutherford (along with Geiger
  and Marsden) direct alpha particles (atomic mass
  2 protons 2 neutrons 4) at thin gold foil
• What did he expect to find?

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History of Atomic Physics

• It was almost as incredible as if you had fired
  a fifteen-inch shell at a piece of tissue and it
  came back and hit you.
• Concluded that the nucleus has a compact
  positive charge and is surrounded by negatively
  charged electrons

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History of Atomic Physics

• Theory was complemented by Niels Bohr in 1913,
  which placed the electrons in definite shells, or
  quantum levels

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Einsteins Equation

• In 1905 while working as a Swiss patent clerk,
  Albert Einstein, published four seminal papers in
  physics, one of which directly pertains to
  nuclear energy

• Consider a nucleus the mass of the composite
  nucleus does not equal the mass of the component
  pieces

mass of nucleus ? mass of pieces alone
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It followed from the special theory of
relativity that mass and energy are both but
different manifestations of the same thing -- a
somewhat unfamiliar conception for the average
mind. Furthermore, the equation E is equal to m
c-squared, in which energy is put equal to mass,
multiplied by the square of the velocity of
light, showed that very small amounts of mass may
be converted into a very large amount of energy
and vice versa. The mass and energy were in fact
equivalent, according to the formula mentioned
before. This was demonstrated by Cockcroft and
Walton in 1932, experimentally."
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Einsteins Equation

• The mass of the nucleus is about 1 smaller than
  the mass of its individual protons and neutrons
• This difference is called the mass defect
• It arises from the energy released when the
  nucleons (protons and neutrons) bind together to
  form the nucleus this energy is called the
  binding energy. The binding energy determines
  which nuclei are stable and how much energy is
  released in a nuclear reaction

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Einsteins Equation

• E mc2 is a consequence of the Special theory
  of relativity
• The implications is that matter and energy are
  interchangeable
• Note! This applies to all energy conversion
  processes
• Because the speed of light is a large number
  (3x108 m/s), a small amount of matter can be
  converted into a tremendous amount of energy.
  This is the key to the power of nuclear weapons
  and nuclear reactors.

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Einsteins Equation

• So, where does the extra mass go? Into
  binding energy
• Can this enormous repository of energy be
  released?
• Rutherford and Einstein quotes
• But, this eventually leads to conception of the
  atomic bomb

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Emc2The Genesis of the Nuclear Age
"I do not consider myself the father of the
release of atomic energy. - Albert Einstein,
Atomic War or Peace, 1945