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16.1 Nuclear Weapons

16.1 Nuclear Weapons - Nuclear Weapons 1 2 3 4 5...

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7/31/2008 Nuclear Weapons 1. Radioactivity 2. Carbon dating 3. Fission 4. Nuclear weapons 5. Nuclear reactors Observations About Nuclear Weapons • They release enormous amounts of energy • They produce incredible temperatures • They produce radioactive fallout • They are relatively hard to make • They use chain reactions Atomic Structure • Atoms are usually electrically neutral – They must have as many + charges as – charges – Each electron must be matched by a + charge • At the center of an atom is its nucleus – Extremely small (1/100,000th of the atom’s diameter) – Contains most of the atom’s mass – Also contains most of the atom’s potential energy Nucleus Structure •The number of protons is the atomic number, which determines the identity of the element . •The number of protons and neutrons determines the atomic mass of the element . • Different isotopes of an element have the same atomic number (same number of protons) but different atomic masses (different number of neutrons) • Neutrons and protons are called nucleons because they are in the nucleus. • The way the nucleons interact via Strong and EM forces determines the nuclear structure. pp nn pn Strong (Nuclear) Force Strong (Nuclear) Force Plus EM force Structure of Nucleus • Two forces are active in a nucleus – Electrostatic repulsion between protons – Strong nuclear force -- attraction between touching nucleons – Short distances: nuclear force stronger than electric – Long distances: electric force stronger than nuclear Nomenclature Mass Number (A) = Protons + Neutrons Atomic Number (Z) = Number of Protons A-Z = Number of Neutrons Na 11 12
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7/31/2008 Clicker Question 1 K 19 39 How many protons? A) 39 B) 19 C) 20 • Stable nuclei group in a band of stability according to their neutron-to-proton ratio. Nuclei outside this band of stability are radioactive. As the size of nuclei increases, so does the neutron-to-proton ratio • For large stable nuclei, there are more neutrons than protons because electric repulsion between protons is long-range. • For small nuclei, the number of protons and neutrons are about equal Nuclear Stability Dots indicate stable nuclei Four Fundamental Forces of Nature 1. Gravitational: Weakest, long range 2. Weak (Nuclear): Short range, responsible for beta decay 3. Electromagnetic: Long range, ~10 36 times stronger than gravity 4. Strong (Nuclear): short range, holds the nucleus together, ~10 6 times stronger than E-M force Radioactivity • Protons repel one another and neutrons are unstable • Therefore, large nuclei have two problems: – Too many protons, then too much electrostatic potential – Too many neutrons, then neutrons are unstable
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