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Radioactive Decay. Half Life. What’s In An Atom?. Electrons: Orbit around the nucleus. Negative charge. Nucleus: Has protons of positive charge and neutrons of no charge. A neutron is a proton and an electron stuck together. Net charge is 0. Neutrons.

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2. What’s In An Atom? Electrons: Orbit around the nucleus. Negative charge. Nucleus: Has protons of positive charge and neutrons of no charge. A neutron is a proton and an electron stuck together. Net charge is 0.

3. Neutrons • The force holding the proton and electron together in a neutron is relatively weak. • Sometimes a neutron will break apart, and the proton will be shot out of the nucleus by the repelling force of the other protons. • Neutron Proton + Electron + - + -

4. Neutrons • Since these protons are so close to the nucleus when they are “set free”, they leave the atom with incredible velocity. • This is one kind of radiation. • When atoms shoot out these protons, they loose some of their mass (since the protons leaving have mass). +

5. Half Life • Def: The amount of time it takes a sample of radioactive material to lose half its mass due to radiation.

6. Half Life • Image a 10 kg sample of radioactive “stuff” with a half life of 5 seconds.

7. Example • A 1.0 kg sample of U-238 (Naturally occurring Uranium) has a half life of 1.41 X 1017 s, or about 4.4 billion years. How much will remain after 3 half lives? How long will that take?

8. Example • A 1.0 kg sample of U-238 (Naturally occurring Uranium) has a half life of 1.41 X 1017 s, or about 4.4 billion years. How much will remain after 3 half lives? How long will that take? • Set up a table:

9. Example • A 1.0 kg sample of U-238 (Naturally occurring Uranium) has a half life of 1.41 X 1017 s, or about 4.4 billion years. How much will remain after 3 half lives? How long will that take? • Insert your givens:

10. Example • A 1.0 kg sample of U-238 (Naturally occurring Uranium) has a half life of 1.41 X 1017 s, or about 4.4 billion years. How much will remain after 3 half lives? How long will that take? • Fill in the table for correct # of half lives.

11. Another Example • Plutonium has a half life of 7.75 x 1011 s. How much will remain of a .10 kg sample after 1.21 x 1013 s?

12. Another Example • Plutonium has a half life of 7.75 x 1011 s. How much will remain of a .10 kg sample after 1.21 x 1013 s? • Table and givens:

13. Another Example • Plutonium has a half life of 7.75 x 1011 s. How much will remain of a .10 kg sample after 1.21 x 1013 s? • Table and givens:

14. Further Exploration • Go to the following website to answer these questions: http://colorado.edu/physics/2000/index.pl • Science Trek → Isotopes and Radioactivity • Balance the following equations: • 7Be4 => 7Li? + ?e1 • 238U? => 234Th90 + ?He2 What is the half life of Neon-19? • What is the half life of Nitrogen-17?

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