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NUCLEAR CHEMISTRY Nuclear Particles: Mass ChargeSymbol Mass ChargeSymbol PROTON 1 amu +1 H+, H, p NEUTRON 1 amu 0 n © Copyright 1994-2001 R.J. Rusay
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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. © Copyright 1994-2001 R.J. Rusay Nuclear decay: reactions conserve mass.
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Nuclear Particles emitted from unstable nucleii Emitted Particles: Mass Charge Symbol Mass Charge Symbol alpha particle 4 amu +2 beta particle very small -1 gamma very very small 0 positron very small +1 © Copyright 1994-2001 R.J. Rusay
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Nuclear Penetrating Power © Copyright 1994-2001 R.J. Rusay alpha particle: low beta particle: moderate gamma: high X-rays? Water
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Alpha Decay–Heavy Elements 238 U 234 Th + + e t 1/2 = 4.48 x 10 9 years t 1/2 = 4.48 x 10 9 years 210 Po 206 Pb + + e t 1/2 = 138 days t 1/2 = 138 days 256 Rf 252 No + + e t 1/2 = 7 ms t 1/2 = 7 ms For Cobalt 60 predict the alpha decay product:
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Beta Decay–Electron Emission n p + + + Energy 14 C 14 N + + Energy t 1/2 = 5730 years t 1/2 = 5730 years 90 Sr 90 Y + + Energy t 1/2 = 30 years t 1/2 = 30 years ? 247 Cm + + Energy t 1/2 = 22 min t 1/2 = 22 min 131 I ??+ + Energy t 1/2 = 8 days t 1/2 = 8 days 247 Am 131 Xe
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Electron Capture–Positron Emission p + + e - n + Energy = Electron capture p + n + e + + Energy = Positron emission 51 Cr + e - 51 V + Energy t 1/2 = 28 days 7 Be 7 Li + + Energy t 1/2 = 53 days ? + e - 177 Hf + Energy 144 Gd ? + + Energy 177 Ta 144 Eu
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Nuclear Decay Predict the Particle or element: Thallium 206 decays to Lead 206. What particle is emitted? Cesium 137 goes through Beta decay. What element is produced and what is its mass? Thorium 230 decays to Radium 226. What particle is emitted? © Copyright 1994-2001 R.J. Rusay
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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 © Copyright 1994-2001 R.J. Rusay
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The 238 U Decay Series
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Radiodating Methods © Copyright 1994-2001 R.J. Rusay Three isotopes are currently used: Carbon-14half 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.
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Decrease in Number of 14 C Nuclei Over Time
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Radiocarbon Dating for Determining the Age of Artifacts An ancient wood sample has 6.25% of the 14 C of a reference sample. What is the age of the sample?
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Nuclear Reactions The mass of the visible universe is 73% H 2 and 25% He. The remaining 2%, “heavy” elements, have atomic masses >4. The “heavy” elements are formed at very high temperatures (T>10 6 o C) 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 1994-2001 R.J. Rusay
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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
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NUCLEAR ENERGY EINSTEIN’S EQUATION FOR THE CONVERSION OF MASS INTO ENERGY E = mc 2 m = mass (kg) c = Speed of light c = 2.998 x 10 8 m/s
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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 -19 J Binding energies are commonly expressed in units of megaelectron volts (Mev) 1 Mev = 10 6 ev = 1.602 x 10 -13 J 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 10 6 ev = 931.5 Mev
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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: © Copyright 1994-2001 R.J. Rusay
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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. Fission: Fusion:
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Nuclear Reactions Nuclear fission was first used in a chain reaction:
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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 10 10 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 R.J.Rusay 1994-2001
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The Nuclear Dawn August 6, 1945
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Nuclear Power Plant
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Worldwide Nuclear Power Plants
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Chernobyl, Ukraine April,1986 and April,2001
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Nuclear Reactions / Fusion 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 © Copyright 1994-2001 R.J. Rusay The application has great promise in producing relatively “clean” abundant energy through the combination of Hydrogen isotopes particularly from 2 H, deuterium and 3 H, tritium: (NIF/National Ignition Facility, LLNL)
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National Ignition Facility Lawrence Livermore National Laboratory
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© Copyright 1994-2001 R.J. Rusay
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