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Using Science to Measure Time  Relative dating (e.g., fossil records)  Electronic dating  Quartzite crystals  Nuclear time clocks.

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Presentation on theme: "Using Science to Measure Time  Relative dating (e.g., fossil records)  Electronic dating  Quartzite crystals  Nuclear time clocks."— Presentation transcript:

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2 Using Science to Measure Time  Relative dating (e.g., fossil records)  Electronic dating  Quartzite crystals  Nuclear time clocks

3 Nuclear Radiation In terms of physics and chemistry, nuclear radioactivity is pretty cool… its’ just unfortunately not as sexy as The Simpsons may have you believe at first.

4 How an Atom Works  Atoms have protons, neutrons, and electrons.  The protons and neutrons are located inside the center of the atom (nucleus)  Protons normally repel other protons. (Why?)  The force that holds together protons can “accidentally” be broken.  What gets released?

5 How an atom works  (view the Javascript)  https://phet.colorado.edu/en/simulation/alpha-decay

6 Types of Nuclear Radiation  Alpha decay  Beta decay  Gamma decay  Shoots off 2 protons & 2 neutrons  Changes a neutron into a proton (or vice versa)  Shoots off a high pocket of energy (no change)

7 Why Does this Even Matter?  Alpha decay  Beta decay  Gamma decay  Shoots off 2 protons & 2 neutrons  Changes a neutron into a proton (or vice versa)  Shoots off a high pocket of energy (no change)

8 Example: Polonium’s Decay Process  Alpha decay  Beta decay  becomes lead  Becomes Astatine or  Becomes bismuth

9 Using Radioactivity for Finding Time  All elements can undergo nuclear radiation except for two (which two do not decay?)  Since even 1 mg of any element has at least atoms in it, we can find the precise moment in time that that sample was made.  All things decay with a certain “reverse J-curve” pattern called a “half life”

10 What Is Half Life?  Half life is the time it takes for exactly one-half of a sample of any element to decay.  Stable atoms have half-lives of millions or billions of years.  Radioactive atoms have half-lives that are very short.

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12  C-14 = 5,730 years  U-235 = 704 million years  K-40 = 1.25 billion years Common Half Lives

13 Further Evidence  Uranium-235 and its decay product (lead) are both created in very different scenarios.  If you find a mixture of uranium/lead, what can you conclude about the lead?  The same goes for potassium-40 and calcium.  If you find a mixture of potassium that also has calcium, what can you conclude about the sample?

14 Questions  An archaeologist finds a clay pot where 12.5% of the expected carbon-14 is remaining.  In Antarctica, a sample of potassium was found where only 6.25% of the expected potassium-40 was left.  C-14 = 5,730 years  K-40 = 1.25 billion years


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