Modern Physics

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Modern Physics

• Model of the atom
• Radioactivity

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Introduction - Today we expand our discussion of
explaining what happens at the nuclear level
atoms.

• Radioactivity (substances that give of invisible
  radiations) and the types of radiations.
• What happens when an atom undergoes radioactivity
  decay
• Uses for radiation
• The types of reactions that cause nuclear
  reactions
• The affects of nuclear reactions on energy

3
Nucleons

• Are particles occupying the nucleus
• Consist of charged protons and neutral neutrons
• Have almost 2000 time the mass of electrons
• Are made of quarks and leptons (building blocks
  of matter, elementary particles)

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Atom
Atomic mass protons neutrons (number
of nucleons)
Atomic number number of protons
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Isotopes

• Atoms of the same element with different numbers
  of neutrons (different masses)

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Radioactive Isotopes

• Has an unstable nucleus
• Spontaneously emits a particle and decay into
  another element.

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Marie Curie Nobel prize winner

• The word radioactivity was first used by Marie
  Curie in 1898.
• She used the word radioactivity to describe the
  property of certain substances to give off
  invisible radiations that could be detected by
  films.

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Radioactive Decay

• Three different kinds of radiation given off by
  radioactive materials
• Alpha rays
• Beta rays
• Gamma rays
• called rays because the radiation carried
  energy and moved in straight lines, like light
  rays.

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• Radioactivity comes from the nucleus of the atom.
  
• If the nucleus has too many neutrons, or is
  unstable the atom undergoes radioactive decay.
• decay - to "break down."

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Atomic Decay

• Alpha decay the nucleus ejects two protons and
  two neutrons.
• Beta decay a neutron in the nucleus splits into
  a proton and an electron.
• Gamma decay occurs because the nucleus is at too
  high an energy. The nucleus falls down to a lower
  energy state and, in the process, emits a high
  energy photon.

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• Radioactive decay gives off energy.
• The energy comes from the conversion of mass into
  energy.
• Because the speed of light (c) is such a large
  number, a tiny bit of mass generates a huge
  amount of energy.
• Radioactivity occurs because everything in nature
  tends to move toward lower energy.

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Radiation

• The flow of energy through space.
• Forms of radiation
• Light
• Radio
• Microwaves
• X-rays
• Many people mistakenly think of radiation as only
  associated with nuclear reactions.

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X-ray machines

• X-rays are photons
• Used to produce images of bones and teeth on
  x-ray film.
• X-ray film turns black when exposed to x-rays.

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X-Rays Uses

• High level therapeutic x-rays are used to
  destroy diseased tissue, such as cancer cells.
• The beams are made to overlap at the place where
  the doctor wants to destroy diseased cells.

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CAT scan

• Computerized Axial Tomography
• Produced by a computer that controls an x-ray
  machine as it takes pictures of the body from
  different angles.
• Produces three-dimensional images of bones and
  other structures within the body.

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Radiation Detection

• The Geiger counter is a type of radiation
  detector invented to tell when radiation is
  present and to measure its intensity.

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Half-life

• The time it takes for half the mass of a
  radioactive sample to decay.
• Ranges from a fraction of a second to billions of
  years.
• Is not affected by external conditions.

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Fusion reactions

• Nuclear reaction that combines, or fuses, two
  smaller nuclei into a larger nucleus.
• It is difficult to make fusion reactions occur
  because positively charged nuclei repel each
  other.

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Fission reactions

• A fission reaction splits up a large nucleus into
  smaller pieces.
• A fission reaction typically happens when a
  neutron hits a nucleus with enough energy to make
  the nucleus unstable.

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Nuclear Reactions and Energy

• A nuclear reaction is any process that changes
  the nucleus of an atom.
• Radioactive decay is one form of nuclear reaction.

21
Nuclear Reactions and Energy

• If you could take apart a nucleus and separate
  all of its protons and neutrons, the separated
  protons and neutrons would have more mass than
  the nucleus did.
• The mass of a nucleus is reduced by the energy
  that is released when the nucleus comes together.
• Nuclear reactions can convert mass into energy.

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Nuclear Reactions and Energy

• Both these nuclear reactions release a small
  portion of the mass as large amounts of energy.
• Nuclear fusion is what powers a modern nuclear
  warhead (hydrogen bomb)
• Nuclear fission (less powerful) occurs in an
  atomic bomb (like the ones used against Japan in
  WWII), or in a nuclear power plant.