106 Nuclear - ChemConnections
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NUCLEAR CHEMISTRY 1 Dr. Ron Rusay Chem 106 Spring 2004 © Copyright 1994-2004 R.J. Rusay NUCLEAR CHEMISTRY Nuclear Particles: 1 Mass Charge Symbol 1 1 1 PROTON NEUTRON 1 amu 1 amu © Copyright 1994-2004 R.J. Rusay +1 0 H+, 1 1 1 H, 1 p 1 0n Nuclear Decay / Radioactivity Unstable nuclei “decay” i.e. they lose particles which lead to other elements and isotopes. The elements and isotopes produced may also be unstable and go through further decay. Nuclear decay: reactions conserve mass. © Copyright 1994-2004 R.J. Rusay QuickTime™ and a Sorenson Video decompressor are needed to see this picture. Nuclear Particles emitted from unstable nucleii Emitted Particles: Mass Charge Symbol alpha particle 4 amu beta particle very small gamma very very small positron very small © Copyright 1994-2004 R.J. Rusay +2 -1 4He2 ;( 4He);4 2 2 2 0e 0 1 1 0 +1 0 1 Nuclear Penetrating Power alpha particle: low beta particle: moderate gamma: high X-rays? Water © Copyright 1994-2004 R.J. Rusay •Dosimeters measure radiation absorbed •Radiation effects are cumulative (Madame Curie) •rad = radiation absorbed dose ( 0.01 J/kg) •rem= radiation equivalent for man (= rad x Q; Q=1 for X-rays,3 for neutrons, 10 for p+, 20 for -particles) •Background radiation = 0.13 rem •Annual limit is set at 0.17 rem above background Alpha Decay–Heavy Elements 238U 234Th + + e t1/2 = 4.48 x 10 9 years 210Po + +e 206Pb t1/2 = 138 days 256Rf 252No 60 27 Co + +e t1/2 = 7 ms For Cobalt 60 predict the alpha decay product: 60 27 Co 4He ? 56 Mn 2 25 Nuclear Decay Series If the nuclei produced from radioactive decay are unstable, they continue to decay until a stable isotope results. An example is Radium which produces Lead 226Ra 206Pb 88 82 © Copyright 1994-2004 R.J. Rusay The 238U Decay Series Radiodating Methods Three isotopes are currently used: Carbon-14 half life 5,730 yrs Potassium-40 half life 1.3 x 10 9 yrs Uranium-238 half life 4.47 x 10 9 yrs The age of samples can be determined by measuring their disintegrations over time. © Copyright 1994-2003 R.J. Rusay Decrease in Number of 14C Nuclei Over Time Radiocarbon Dating for Determining the Age of Artifacts An ancient wood sample has 6.25% of the 14C of a reference sample. What is the age of the sample? Nuclear Reactions The mass of the visible universe is 73% H2 and 25% He. The remaining 2%, “heavy” elements, have atomic masses >4. The “heavy” elements are formed at very high temperatures (T>10 6 oC) by FUSION, i.e. nuclei combining to form new elements. There is an upper limit to the production of heavy nuclei at A=92, Uranium. Heavy nuclei split to lighter ones by FISSION © Copyright 1994-2003 R.J. Rusay NUCLEAR STABILITY Patterns of Radioactive Decay Alpha decay ()–heavy isotopes Beta decay () –neutron rich isotopes Positron emission ()–proton rich isotopes Electron capture–proton rich isotopes x-rays Gamma-ray emission () Spontaneous fission–very heavy isotopes © Copyright 1994-2003 R.J. Rusay NUCLEAR ENERGY EINSTEIN’S EQUATION FOR THE CONVERSION OF MASS INTO ENERGY 2 E = mc m = mass (kg) c = Speed of light 8 c = 2.998 x 10 m/s Mass Energy Electron volt (ev) The energy an electron acquires when it moves through a potential difference of one volt: 1 ev = 1.602 x 10-19J Binding energies are commonly expressed in units of megaelectron volts (Mev) 1 Mev = 106 ev = 1.602 x 10 -13J A particularly useful factor converts a given mass defect in atomic mass units to its energy equivalent in electron volts: 1 amu = 931.5 x 106 ev = 931.5 Mev Nuclear Reactions Fission and Fusion reactions are highly exothermic (1 Mev / nucleon). This is 10 6 times larger than “chemical” reactions which are about 1 ev / atom. Nuclear fission was first used in a chain reaction: 235U 1n236U 141Ba 92Kr3 1n 36 0 92 0 92 56 © Copyright 1994-2003 R.J. Rusay Nuclear Reactions: Fission: Fusion: Fission and Fusion reactions are highly exothermic (1 Mev / nucleon). This is 10 6 times larger than “chemical” reactions which are about 1 ev / atom. Nuclear Reactions Nuclear fission was first used in a chain reaction: 235U 1n236U141Ba 92Kr3 1n 36 0 92 0 92 56 Nuclear Reactions / Fission The Fission Chain Reaction proceeds geometrically: 1 neutron -> 3 -> 9 -> 27 -> 81 etc. 1 Mole of U-235 (about 1/2 lb) produces 2 x 1010 kJ which is equivalent to the combustion of 800 tons of Coal! Commercial nuclear reactors use fission to produce electricity....Fission bombs were used in the destruction of Hiroshima and Nagasaki, Japan, in August 1945. © Copyright 1994-2003 R.J. Rusay The Nuclear Dawn August 6, 1945 QuickTime™ and a Cinepak decompressor are needed to see this picture. Nuclear Power Plant Worldwide Nuclear Power Plants Chernobyl, Ukraine April,1986 and April,2001 Nuclear Reactions / Fusion http://crystals.llnl.gov Fusion has been described as the chemistry of the sun and stars. It too has been used in weapons. It has not yet found a peaceful commercial application The application has great promise in producing relatively “clean” abundant energy through the combination of Hydrogen isotopes particularly from 2H, deuterium and 3H, tritium: (NIF/National Ignition Facility, LLNL) 2H3H4He 1n18.38MeV 0 © Copyright 1994-2004 R.J. Rusay National Ignition Facility Lawrence Livermore National Laboratory National Ignition Facility Lawrence Livermore National Laboratory © Copyright 1994-2004 R.J. Rusay
