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Nuclear Equations Nuclear Equations In nuclear equations, we balance nucleons (protons and neutrons). The atomic number (number of protons) and the mass number (number of nucleons) are conserved during the reaction. Nuclear Equations Alpha Decay Nuclear Equations Beta Decay Nuclear Equations Beta Decay Nuclear Equations Positron Emission: A positron is a particle equal in mass to an electron but with opposite charge. Nuclear Equations Electron Capture: A nucleus absorbs an electron from the inner shell. Nuclear Equations EXAMPLE 4.1 Balancing Nuclear Equations Write balanced nuclear equations for each of the following processes. In each case, indicate what new element is formed. a. Plutonium-239 emits an alpha particle when it decays. b. Protactinium-234 undergoes beta decay. c. Carbon-11 emits a positron when it decays. d. Carbon-11 undergoes electron capture. EXAMPLE 4.1 Balancing Nuclear Equations continued Exercise 4.1 Write balanced nuclear equations for each of the following processes. In each case, indicate what new element is formed. a. Radium-226 decays by alpha emission. b. Sodium-24 undergoes beta decay. c. Gold-188 decays by positron emission. d. Argon-37 undergoes electron capture. EXAMPLE 4.2 More Nuclear Equations 5 In the upper atmosphere, a nitrogen-14 nucleus absorbs a neutron. A carbon-14 nucleus and another particle are formed. What is the other particle? Half-Life Half-life of a radioactive sample is the time required for ½ of the material to undergo radioactive decay. Half-Life Half-Life Fraction Remaining = 1/2n Half-life T1/2 = 0.693/ k(decay constant) If you know how much you started with and how much you ended with, then you can determine the number of half-lives. If you also know the start and end time, you can divide the time by the number of half- lives to give you the T1/2. Half-life To determine starting amounts or ending amounts: ln(Nt/No) = -kt Nt is the number of radioactive nuclei at your ending No is the number of radioactive nuclei at the start K is the decay constant Radioisotopic Dating Radioisotopic Dating Carbon-14 Dating: The half-life of carbon-14 is 5730 years. Carbon-14 is formed in the upper atmosphere by the bombardment of ordinary nitrogen atoms by neutrons from cosmic rays. Radioisotopic Dating Tritium Dating: Tritium is a radioactive isotope of hydrogen. It has a half-life of 12.26 years and can be used for dating objects up to 100 years old. Nuclear Chain Reaction Fission of one nucleus produces neutrons that can cause the fission of other nuclei, thus setting off a chain reaction. Manhattan Project The Manhattan Project was launched by President Roosevelt in 1939. It consisted of 4 separate research teams attempting to: a. Sustain the nuclear fission reaction. b. Enrich uranium. c. Make fissionable plutonium-239. d. Construct a fission atomic bomb. Manhattan Project Replicas of “Little Boy” (dropped on Hiroshima) and “Fat Man” (dropped on Nagasaki). Manhattan Project Mushroom cloud over Nagasaki from the detonation of “Fat Man,” August 9, 1945. Radioactive Fallout Many radioactive isotopes are produced in a nuclear bomb blast. Some are particularly harmful to humans. Among these are strontium-90 and iodine-131. Strontium-90: Half-life = 28.5 years, chemically similar to calcium. Obtained from dairy and vegetable products and accumulates in bone. Iodine-131: Half-life = 8 days. Concentrates in the thyroid glands. Nuclear Power Plants Civilian nuclear power plants use less enriched uranium (2.5-3.5% uranium-235 rather than 90% for weapons-grade). The nuclear chain reaction is controlled for the slow release of heat energy. The heat is used to make steam, which turns a turbine to produce electricity. The Nuclear Age .
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