Radioactivity

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Radioactivity
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What is Radiation?

• Radiation - particles or energy released from a
  nucleus during radioactive decay.
• Radioactive decay is the spontaneous
  disintegration of a nucleus into a smaller
  nucleus

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The Nucleus

• The nucleus is composed of nucleons the protons
  and neutrons.
• Protons - positive
• Neutrons - neutral

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Mass Defect

• Mass defect is the difference between the mass of
  all the particles in an atom and the actual mass
  of the atom.
• This missing mass is related to the energy
  needed to break the nucleus apart.

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What makes an atom radioactive?

• A nucleus may be unstable if the ratio between
  neutrons and protons is greater than 1.5 to 1.
• If the ratio is closer to 11 then the nucleus is
  more stable.

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What happens to a radioactive nucleus?

• A nuclear reaction is a change in the nucleus.
• A transmutation is a type of change where the
  identity of the atoms changes.
• What would change the identity of an atom?

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Alpha Decay

• Alpha decay of a nucleus produces a lighter
  nucleus and an alpha particle.
• An alpha particle (a) is made up of 2 protons and
  2 neutrons.

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Beta Decay

• Beta decay of a nucleus results in a new element
  with the same mass and a beta particle.
• A beta particle (ß) is the same as an electron.

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Gamma Decay

• During Gamma (?) decay only energy is released
  from the nucleus.
• Gamma decay often follows other types of changes.

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Rate of Decay

• Half-life is the term used to describe the time
  needed for half the atoms in a sample of
  radioactive material to change.
• Half-life times can vary greatly
• Cobalt 60 10.5 minutes
• Carbon 14 5715 years
• Uranium 238 4.5 billion years

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Half life Diagram
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Decay Series
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Artificial Transmutations

• New man-made (synthetic) elements can be made in
  particle accelerators.
• Produces the Transuranium elements.

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Radiation exposure

• Alpha low energy, doesnt penetrate
• Beta higher energy, penetrates, short range
• Gamma much higher energy, hard to stop.

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Detecting Radiation

• Geiger counters measure radiation by detecting
  gas ionized (charged) by radioactive particles.
• Film badges can measure exposure to radiation.

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Using Radiation
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Radioactive Dating

• Determining the approximate age of a material by
  measuring the amount of radioactive material left
  over and comparing it to the amount that has
  changed.
• This allows us to estimate the age of rocks,
  organic materials and the Earth!

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Medicine

• Radioactive tracers are materials that can be
  safely placed in the body to track movement of
  materials.
• Radiation can also be used to kill cancerous
  cells.

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Agriculture

• Tracers can be used to track movement of
  materials in plants.
• Radiation can be used to kill insects and
  bacteria.

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Energy

• Nuclear power plants use heat from nuclear
  reactions to generate electricity.
• Process uses
• Fuel rods
• Control rods
• Moderators

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Nuclear Waste

• Waste must be given time to decay into safer
  elements, and that may take thousands of years.
• Currently waste is contained at 77 sites across
  the country.
• The materials are buried in specially designed
  cases.

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Fission

• In fission a heavy nucleus splits to form lighter
  nuclei with the release of energy.
• Fission may start a chain reaction where one
  split starts more.
• Fission is used in nuclear power plants.

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Fusion

• In fusion lighter nuclei combine to form a
  heavier nucleus with the release of energy.
• Uncontrolled fusion is the process in more
  advanced nuclear weapons.
• Stars use fusion to combine hydrogen atoms into
  helium. Energy is released.

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Pioneers of Radioactivity
Clockwise from left Wilhelm Roentgen, Henri
Becquerel, Marie and Pierre Curie, Hans Geiger,
and Enrico Fermi.