10.2 Nuclear Forces • forces between protons and _____________ in the nuclei of atoms • the stability of the nucleus depends on these forces Strong Nuclear Force ­ holds protons (+) and neutrons (no charge) together In a stable atom, the attractive forces are stronger than the repulsive forces, and the element does not undergo decay. Too many neutrons or protons can cause a nucleus to become _________ and __________. Example: nuclei with > 83 protons are always unstable and decay REMEMBER, decay results in more stable nuclei. 1 Nuclear Fission Definition: process of splitting heavier nuclei into lighter nuclei • During fission, both neutrons and energy are released. Albert Einstein explained how matter can be converted into energy and energy into matter with his theory of relativity in 1905. E = mc2 2 Chain Reactions (Fission) Analogy: shooting marbles or dominoes Neutron strikes a nuclei ­­> splits ­­> neutrons are emitted and strike other nuclei causing them to split If every Uranium atom emits 2 neutrons when split, then these neutrons can split 2 more U atoms, which will produce more neutrons to split add'l atoms, etc. 3 This sounds like how Nuclear Reactors work: a controlled chain reaction can be used to generate electricity by using the energy given off to heat water, which makes steam, which rotates a turbine to generate electricity. Control rods are used to regulate fission by slowing down the chain reaction. 4 The Power of Fission • U.S. receives about 20% of its power from nuclear power plants. • Around the world, there are 440 nuclear reactors that generate electriticy, > 400 that power ships and submarines, and a bit less than 300 that are used for research. • France is the world's leader in using nuclear power for electricity (>75%). 5 Nuclear Fusion Definition: combining light nuclei to form heavier nuclei. • This process occurs in the sun (Hydrogen nuclei fuse to make Helium) and is used to make nuclear bombs. • A LOT of energy is needed to start a fusion reaction. • Major problem with fusion: must occur at VERY high temperatures (100's of millions of C). http://www.cosmolearning.com/videos/fission­and­fusion/ 6 7.