environmental science introduction to nuclear energy lecture notes
TRANSCRIPT
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Environmental ScienceIntroduction to Nuclear Energy
Lecture Notes
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Nuclear energy = the energy trapped inside an atom• Nuclear energy was first
introduced in 1945, when two fission bombs were used against Japan
Little Boy
Fat Man
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QUICK REVIEW ATOMSNUCLEUSPROTONSNEUTRONSELECTRONSELEMENTS
• In most atoms . . .
# Protons = # Neutrons• Atomic Number =
• Atomic Mass =
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*Atomic (Proton) Number vs. *Atomic Mass vs. *Neutron Number
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ISOTOPES• ISOTOPES=
• EXAMPLE:
• Carbon-12 and Carbon-16• How many protons and neutrons would each atom
contain?
Isotopes Video
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Comprehension Check• Circle each atom at right
that would be an isotope of the atom below. Look on the period table, what element does the atom below represent?
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• Most isotopes of atoms are stable, but, sometimes this is not the case:– Radium-226 (the name of the atom is radium, its atomic mass is
226)
• RADIOACTIVITY: the nucleus of Radium-226 is unstable and breaks down and release energy and atomic sub-particles. The release of these particles is radioactivity.
• When a radium atom breaks down (decays), a sub-atomic particle flies out of the nucleus at a high speed. This releases energy.
• Isotopes try to decay to more stable isotopes.
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When They Decay, Atoms Emit One of the Following:
1. Alpha Particles: equivalent to 2 protons + 2 neutrons (He-4 nucleus)
• They travel only a few inches through air and can easily be stopped with a sheet of paper.
Radioactive Decay Video
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2. Beta Particles: electrons
• Beta particles can travel a few feet through air and can be stopped with a few sheets of aluminum foil.
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3. Gamma Rays: high frequency photons (electromagnetic wave)
• Gamma radiation is able to travel many meters in air and many centimeters in human tissue. It readily penetrates most materials and is sometimes called "penetrating radiation."
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• The half-life of an isotope is the amount of time it takes for half of the atoms to decay into a more stable form.
• Naturally abundant isotopes exist around us because their half-lives are longer than the age of the earth.
Calculating Half Life Problems
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EXAMPLES:• Uranium 238 (238U) has a half-life of 4.5
billion years so it is naturally abundant.
• Most isotopes have short half-lives and must be produced in the laboratory to study or use.
• Cobalt-60 (Co-60) has a half-life of 5.3 years and is made in a reactor. Co-60 is used for radiation therapy of cancer patients.
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PROBLEMS1. How can you tell if you have an isotope?
– See Periodic Table of Elements– Check Atomic Mass– If different than Periodic Table, you have an
isotope
• EXAMPLE: Is Calcium-35 an isotope? If so, of what atom is it an isotope?
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2. How many protons and neutrons does Calcium-35 contain?
– See Periodic Table of Elements– Check Atomic Number– Subtract Atomic Number from Atomic Mass
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3. An isotope of cesium (cesium-137) has a half-life of 30 years. If 1.0 mg of cesium-137 decays over a period of 90 years, how many mg of cesium-137 would remain?