Radioactivity and its Uses

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Radioactivity and its Uses

• Chapter 18

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Standards

• PS 2.6 Compare fission and fusion (including
  that basic processes and the fact that both
  fission and fusion convert a fraction of the mass
  of interacting particles into energy and release
  a great deal of energy).
• PS 2.7 Explain the consequences that the use of
  nuclear applications (including medical
  technologies, nuclear power plants, and nuclear
  weapons) can have.

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What Causes Radioactivity?

• Nucleus made of protons and neutrons
• protons and neutrons held together in tightly
  packed nucleus by the strong force

strong force acts over very small distances only!
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What is Radioactivity?

• Nuclear decay which happens when the strong force
  is not large enough to hold the nucleus together
  nucleus gives off matter and energy
• A nucleus with too many or too few neutrons
  compared to protons is radioactive
• Question?
• Why are large nuclei more likely to be
  radioactive than small nuclei?

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Radioactivity and Nuclear Reactions
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Fission

• when a neutron is fired into a nucleus, the
  nucleus splits and a lot of energy is released
  (Emc2)
• only happens with large nuclei such as uranium
  and polonium
• to divide
• LOTS of energy given off
• Used in nuclear
• reactors/power plants
• to turn water into steam
• which turns a turbine to
• generate electricity

10n 23592U ? 9136Kr 14256Ba 310n
energy
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Chain Reactions

• 3 neutrons released by first reaction can cause
  fission in three more nuclei
• process grows exponentially
• 3 ? 9 ? 27 ? 81 ? 243 ? 729
• this is called a chain reaction an ongoing
  series of fission reactions
• - in power plants and nuclear reactors control
  rods, neutron absorbers, are used to slow down
  the chain reaction

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Critical Mass ?

• In order for a chain reaction to occur, there
  must be a certain minimum amount of
• critical mass - the amount of fissionable
  material in close proximity for a chain reaction
  to occur.
• The mass of the products of a fission reaction
  are less than the mass of the reactants
• This lost mass is converted into energy.
• The conversion of mass to energy during a nuclear
  reaction involves more energy than the amount of
  energy involved in a chemical reaction

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Fusion

• the combining of two small nuclei
• requires very high temperatures (1 million ?C)

process that occurs in stars
11H 21H ? 32He energy
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Radioactivity in Medicine

• Tracer radioactive isotope used to follow how a
  molecule travels through your body or through any
  process scientists wish to monitor
• red flag on a molecule
• Benefits can target certain cells, such as
  cancer cells
• We tag them with radioactive samples of the same
  substance in questionthe radioactivity can be
  traced by Geiger counter or gamma cameras
• Possible drawbacks Waste
• must be stored until it is no
• longer radioactive
• Also kills healthy cells

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• examples
• iodine 131 (emits beta particles and gamma
  rays) - used to detect thyroid problems
• fluorine 18 used in PET scans to detect brain
  problems
• gold 198, iridium 192 injected into
  cancerous cells to kill the cells
• cobalt 60 gamma rays from isotope used to
  kill cancerous cells from outside the body

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Other uses ?

• Nuclear Weapons-
• Benefits
• Some people think they deter war
• Drawbacks
• Smuggling of material possible
• Tremendous amounts of destruction
• Contamination of environment
• Wastecould leak radioactive isotopes and be
  harmful long-term

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• Nuclear Reactors-
• Benefits
• Tremendous amounts of energy from little material
• No greenhouse gases
• Can be used anywhereuses no fossil fuels
• Drawbacks
• Pollute water systems
• Requires specialized technology
• Waste
• Exposure to workers
• Accidents of poorly maintained facilities (ex
  Chernobyl)

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Nuclear power plant