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What is it to be Radioactive?
• Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.
• There are numerous types of radioactive decay. The general idea:
• An unstable nucleus releases energy to become more stable
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Nuclear Reactions• Fission: Bombarding
substances with neutrons and splitting an atom into 2 smaller (what we can do in nuclear power plants)
• Fusion: Joining two atoms into one, creating a different element (what occurs in stars)
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Nuclear energy: energy produced from changes to the nucleus of an atom
1) fusion: joining atoms (sun)
2)fission: splitting atoms (nuclear power plants)
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Three Common Types of Radioactive Emissions
Alpha
Beta
Gamma
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Science Park HS -- Honors Chemistry
Kinds of Radioactivity
The three main decays are Alpha, Beta and Gamma
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Alpha Decay• When two protons and two neutrons (a
Helium nucleus) are ejected from the nucleus. Can be stopped with a piece of paper
Uranium Thorium
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Beta Decay• Beta particles : electrons ejected from the
nucleus when neutrons decay n -> p+ +-
• Can be stopped by aluminum foil or a block of wood.
Thorium Protactinium
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• Gamma radiation • electromagnetic energy
• that is released.
• Gamma rays are electromagnetic waves.
• They have no mass.• Gamma radiation has no charge.
– Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.
Gamma Decay
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Radioactive Half-Life (t1/2 ):
• The time for half of the radioactive nuclei in a given sample to undergo decay.
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Common Radioactive Isotopes
Isotope Half-Life Radiation Emitted
Carbon-14 5,730 years
Radon-222 3.8 days
Uranium-235 7.0 x 108 years
Uranium-238 4.46 x 109 years
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Radioactive Half-Life
• After one half life there is 1/2 of original sample left.
• After two half-lives, there will be
1/2 of the 1/2 = 1/4 the original sample.
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Example
You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.
• How many grams are left after one half-life?
• How many grams are left after two half-lives?