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November 3,2011. Objective: Determine half life of pennies. Agenda: Notes Fossils Lab : Radioactive Decay Review for test. WHAT IS RADIOACTIVE DATING?. Most elements exist in several forms. These are isotopes. Example: Carbon. Radioactive decay. Same atomic # = same # of protons.
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Objective:Determine half life of pennies • Agenda: • Notes • Fossils • Lab: Radioactive Decay • Review for test
Most elements exist in several forms. These are isotopes. Example: Carbon
Radioactive decay • Same atomic # = same # of protons. • Different atomic mass = different # of neutrons. • The nucleus contains protons and neutrons, which is most of the mass. • Some atoms have an unstable nucleus. • These atoms are radioactive. • These elements can turn into other elements. • This is called radioactive decay.
Half-life • The half-life of an isotope is the amount of time it takes for exactly half of the atoms to decay. At the end of one half-life, half of the original atoms will have decayed. • 1st half-life 1/2 of original left • 2nd half-life 1/4 of original left • 3rd half-life 1/8 of original left • 4th half-life 1/16 of original left
Radioactive dating • Half-lives can be used to estimate the age of rocks. We usually need to use isotopes with long half-lives because rocks can be billions of years old.
Radioactive Isotopes Carbon -14 has a short half-life of 5700 years. Uranium-238has an extremely long half-life of 4.5 billion years. Potassium-40has a half-life of 1.25 million years.
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Fossil observations • Draw 7 fossils • Observation • Inference