Published on October 13, 2007
Chapter 26: Nuclear Chemistry: Philip Dutton University of Windsor, Canada N9B 3P4 Prentice-Hall © 2002 General Chemistry Principles and Modern Applications Petrucci • Harwood • Herring 8th Edition Chapter 26: Nuclear Chemistry Contents: Contents 26-1 The Phenomenon of Radioactivity 26-2 Naturally Occurring Radioactive Isotopes 26-3 Nuclear Reactions and Artificially Induced Radioactivity 26-4 Transuranium Elements 26-5 Rate of Radioactive Decay 26-6 Nuclear Stability 26-7 Nuclear Fission Contents: Contents 26-8 Nuclear Fusion 26-9 Effect of Radiation on Matter 26-10 Applications of Radioisotopes Focus On Radioactive Waste Disposal 26-1 The Phenomenon of Radioactivity: 26-1 The Phenomenon of Radioactivity Alpha Particles, : Nuclei of He atoms, 4He2+. Low penetrating power, stopped by a sheet of paper. 2 The sum of the mass numbers must be the same on both sides. The sum of the atomic numbers must be the same on both sides Beta Particles, -: Beta Particles, - Electrons originating from the nuclei of atoms in a nuclear decay process. Simplest process is the decay of a free neutron: Positrons, +: Positrons, + Simplest process is the decay of a free proton: Commonly encountered in artificially produced radioactive nuclei of the lighter elements: Electron Capture and Gamma Rays: Electron Capture and Gamma Rays Electron capture achieves the same effect as positron emission. 202Ti 81 201Hg 80 0 -1 + → ‡ 201Hg 80 → + X-ray Tunneling Out of the Nucleus: Tunneling Out of the Nucleus 26-2 Naturally Occurring Radioactive Isotopes: 26-2 Naturally Occurring Radioactive Isotopes Daughter nuclides are new nuclides produced by radioactive decay. Radioactive Decay Series for 238U: Radioactive Decay Series for 238U 92 Marie Sklodowska Curie: Marie Sklodowska Curie Shared Nobel Prize 1903 Radiation Phenomenon Nobel Prize 1911 Discovery of Po and Ra. 26-3 Nuclear Reactions and Artificially Induced Radioactivity: 26-3 Nuclear Reactions and Artificially Induced Radioactivity Rutherford 1919. Irene Joliot-Curie. Shared Nobel Prize 1938 26-4 Transuranium Elements: 26-4 Transuranium Elements + → + + → 0 n -1 239 Np 93 Cyclotron: Cyclotron 26-5 Rate of Radioactive Decay: 26-5 Rate of Radioactive Decay The rate of disintegration of a radioactive material – called the activity, A, or the decay rate – is directly proportional to the number of atoms present. ln Nt N0 = -λt Radioactive Decay of a Hypothetical 31P Sample: Radioactive Decay of a Hypothetical 31P Sample Table 26.1 Some Representative Half-Lives: Table 26.1 Some Representative Half-Lives Radiocarbon Dating: Radiocarbon Dating In the upper atmosphere 14C forms at a constant rate: Live organisms maintain 14C/13C at equilibrium. Upon death, no more 14C is taken up and ratio changes. Measure ratio and determine time since death. Mineral Dating: Mineral Dating Ratio of 206Pb to 238U gives an estimates of the age of rocks. The overall decay process (14 steps) is: The oldest known terrestrial mineral is about 4.5 billion years old. This is the time since that mineral solidified. + 8 → 0 -1 + 6 26-6 Energetics of Nuclear Reactions: 26-6 Energetics of Nuclear Reactions E = mc2 All energy changes are accompanied by mass changes (m). In chemical reactions ΔE is too small to notice m. In nuclear reactions ΔE is large enough to see m. 1 MeV = 1.602210-13 J If m = 1.0 u then ΔE =1.492410-10 J or 931.5 MeV Nuclear Binding Energy: Nuclear Binding Energy Average Binding Energy as a Function of Atomic Number: Average Binding Energy as a Function of Atomic Number 26-7 Nuclear Stability: 26-7 Nuclear Stability Shell Theory Neutron-to-Proton Ratio: Neutron-to-Proton Ratio 26-8 Nuclear Fission: 26-8 Nuclear Fission Nuclear Fission: Nuclear Fission Enrico Fermi 1934. In a search for transuranium elements U was bombarded with neutrons. emission was observed from the resultant material. Otto Hahn, Lise Meitner and Fritz Stassman 1938. Z not greater than 92. Ra, Ac, Th and Pa were found. The atom had been split. Nuclear Fission: Nuclear Fission → 1n 0 + 1 1n 0 + 3 Fission fragments + 3.2010-11 J Energy released is 8.2107 kJ/g U. This is equivalent to the energy from burning 3 tons of coal Nuclear Reactors: Nuclear Reactors The Core of a Reactor: The Core of a Reactor Nuclear “Accidents”: Nuclear “Accidents” Three Mile Island – partial meltdown due to lost coolant. Chernobyl – Fault of operators and testing safety equipment too close to the limit. France – safe operation provides 2/3 of power requirements for the country. Breeder Reactors: Breeder Reactors Fertile reactors produce other fissile material. → n 1 0 + 1 0 -1 → + 0 -1 → + Disadvantages of Breeder Reactors: Disadvantages of Breeder Reactors Liquid-metal-cooled fast breeder reactor (LMFBR). Sodium becomes highly radioactive in the reactor. Heat and neutron production are high, so materials deteriorate more rapidly. Radioactive waste and plutonium recovery. Plutonium is highly poisonous and has a long half life (24,000 years). 26-9 Nuclear Fusion: 26-9 Nuclear Fusion Fusion produces the energy of the sun. Most promising process on earth would be: Plasma temperatures over 40,000,000 K to initiate a self-sustaining reaction (we can’t do this yet). Lithium is used to provide tritium and also act as the heat transfer material – handling problems. Limitless power once we start it up. Tokomak: Tokomak 26-10 Effect of Radiation on Matter: 26-10 Effect of Radiation on Matter Ionizing radiation. Power described in terms of the number of ion pairs per cm of path through a material. P > P > P Primary electrons ionized by the radioactive particle may have sufficient energy to produce secondary ionization. Ionizing Radiation: Ionizing Radiation Geiger-Müller Counter: Geiger-Müller Counter Radiation Dosage: Radiation Dosage 1 rad (radiation absorbed dose) = 0.001 J/kg matter 1 rem (radiation equivalent for man) = radQ Q = relative biological effectiveness Table 26.4 Radiation Units: Table 26.4 Radiation Units 26-11 Applications of Radioisotopes: 26-11 Applications of Radioisotopes Cancer therapy. In low doses, ionizing radiation induces cancer. In high doses it destroys cells. Cancer cells are dividing quickly and are more susceptible to ionizing radiation than normal cells. The same is true of chemotherapeutic approaches. Radioactive Tracers: Radioactive Tracers Tag molecules or metals with radioactive tags and monitor the location of the radioactivity with time. Feed plants radioactive phosphorus. Incorporate radioactive atoms into catalysts in industry to monitor where the catalyst is lost to (and how to recover it or clean up the effluent). Iodine tracers used to monitor thyroid activity. Structures and Mechanisms: Structures and Mechanisms Radiolabeled (or even simply mass labeled) atoms can be incorporated into molecules. The exact location of those atoms can provide insight into the chemical mechanism of the reaction. Analytical Chemistry: Analytical Chemistry Neutron activation analysis. Induce radioactivity with neutron bombardment. Measure in trace quantities, down to ppb or less. Non-destructive and any state of matter can be probed. Precipitate ions and weigh them to get a mass of material. Incorporate radioactive ions in the precipitating mixture and simply measure the radioactivity. Radiation Processing: Radiation Processing Focus On Radioactive Waste Disposal: Focus On Radioactive Waste Disposal Focus On Radioactive Waste Disposal: Focus On Radioactive Waste Disposal Low level waste. Gloves, protective clothing, waste solutions. Short half lives. After 300 years these materials will no longer be radioactive. High level waste. Long half lives. Pu, 24,000 years and extremely toxic. Reprocessing is possible but hazardous. Recovered Pu is of weapons grade. Chapter 26 Questions: Chapter 26 Questions Develop problem solving skills and base your strategy not on solutions to specific problems but on understanding. Choose a variety of problems from the text as examples. Practice good techniques and get coaching from people who have been here before.