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Published byLorraine Bradley Modified over 9 years ago
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7.2 Nuclear Fission and Fusion
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Nuclear Fission Why are some elements radioactive? There is an optimal ratio of neutrons to protons 1 : 1 for smaller atoms 1.5 : 1 for larger atoms excessive number of neutrons nucleus becomes unstable decays to a more stable state with the release of energy
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Nuclear Fission Lise Meitner (1878-1968)Otto Hahn (1879-1968)
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Nuclear Fission Meitner and Hahn bombarded uranium with neutrons: Kr 36 93 U 92 235 + n 0 1 Ba 56 140 + n 0 1 + 3 the uranium atom becomes unstable and splits into two lighter atoms nuclear fission fission of uranium also produces more neutrons + LOTS of energy
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Nuclear Fission
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Chain Reaction
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Requires a minimum amount of fissionable material critical mass
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Chain Reaction Generation of a critical mass forms the basis of fission bombs
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Mass Defect Mass cannot be created or destroyed Energy cannot be created or destroyed But: mass can be converted into energy and energy can be converted into mass E = m c 2 Albert Einstein (1879-1955) speed of light
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Nuclear Fusion Nuclear Fusion powers the sun H 1 1 4 He 2 4 + Fusion of hydrogen to form helium releases more energy than fission of uranium Hydrogen-, thermonuclear- or fusion bomb Fusion reactors (produce less dangerous radioactive isotopes) + energy
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