2 Radiometric Datingin amount of radioactivity of a radionuclide is predictable & not affected by envrnmntal factorsBy measuring & comparing ratio of parent radioactive isotope to its stable daughter we can determine age of the object(by using t½ & previous equations)Tro: Chemistry: A Molecular Approach
3 Radiometric Dating Mineral (geological) dating compare amount of U-238 to Pb in volcanic rocks and meteoritesPb-206 from decay has unique “signature”dates Earth: btwn 4.0 & 4.5 billion yrs. oldCan also compare amount of K-40 to Ar-40Tro: Chemistry: A Molecular Approach
4 Radiocarbon Dating All things alive (or once alive) contain carbon 3 isotopes of C exist in nature: C-12, C-13, and C–14, which is radioactiveC–14 radioactive half-life = _________ yrsrelatively short half-life - should have disappeared long agoTro: Chemistry: A Molecular Approach
6 CO2 in air source of all C in organism While still living, C–14/C–12 is constant because organism replenishes CCO2 in air source of all C in organismDeath: C–14/C–12 ratio decreasesTro: Chemistry: A Molecular Approach
7 Measure:C–14/C–12 ratio in (once living) artifact & compare to C–14/C–12 ratio in living organism date artifactLimit ~ 50,000 years old. Why?Tro: Chemistry: A Molecular Approach
8 % C-14 (compared to living organism) Object’s Age (in years) Radiocarbon Dating% C-14 (compared to living organism)Object’s Age (in years)100%90%87080%185060%422050%573040%758025%11,50010%19,0005%24,8001%38,100Tro: Chemistry: A Molecular Approach
9 An ancient skull gives 4.50 dis/min∙g C. If a living organism gives 15.3 dis/min∙g C, how old is the skull?Given:Find:ratet1/2 = 4.50 dis/min∙gC, ratet1/2 = 15.3 dis/min∙gCtime, yrConceptual Plan:Relationships:t1/2krate0, ratett+Solve:Check:units are correct, the magnitude makes sense because it is less than 2 half-livesTro: Chemistry: A Molecular Approach
10 Tro: Chemistry: A Molecular Approach Clicker question: Archeologists have dated a civilization to 15,600 yrs ago. If a living sample gives 20.0 counts / min g C, what would be the # of counts per min g C for a rice grain found at the site?3.03 counts / min g C1.209 x 104 counts / min g C20.2 counts / min g CA rice grain? What are you nuts?Tro: Chemistry: A Molecular Approach
11 + Given: Find: Conceptual Plan: Relationships: Solve: Check: t = 15,600 yr, rate0 = 20.0 counts/min∙gCratet, counts/min∙gCConceptual Plan:Relationships:t1/2krate0, tratet+Solve:Check:units are correct, the magnitude makes sense because it is between 10 and 25% of the original activityTro: Chemistry: A Molecular Approach11
12 Nonradioactive Nuclear Changes A few unstable split iif hit just right by a neutron two smaller nuclei = ____________Small nuclei accelerated until they overcome their charge repulsion & smash together larger nucleus = _____________Both fission and fusion release enormous amounts of energyLise MeitnerTro: Chemistry: A Molecular Approach
14 Fission Chain Reaction A chain reaction: when a reactant in the process is also a product of the processin fission 3 neutronsonly need small # of on to start chain rxtnMany on’s produced in fission:ejected from U before hitting another U-235or absorbed by surrounding U-238Minimum amount of fissionable isotope needed to sustain chain rxtn = critical massTro: Chemistry: A Molecular Approach
16 Fossil Nuclear Reaction in West Africa Pitchblende Uranium Oxide ore
17 Natural uranium is < 1% U–235 rest mostly Fissionable isotopes:U–235, Pu–239, & Pu–240Natural uranium is < 1% U–235rest mostlynot enough _______ to sustain chain reactionTo produce fissionable uranium, natural uranium must be enriched in U–235to ~ ___% for “weapons grade”to ~ ___% for reactor gradeTro: Chemistry: A Molecular Approach
18 Nuclear Power Nuclear reactors use fission to generate electricity about ____% of U.S. electricityuses fission of U–235 to produce heatHeat boils water, turning it to steamTro: Chemistry: A Molecular Approach
19 Nuclear Power Plants vs. Coal-Burning Power Plants Use ~ __________ kg of fuel to generate enough electricity for 1 million peopleProduce NO2 & SOx that add to acid rainProduce CO2 that adds to the greenhouse effectUse about ____ kg of fuel to generate enough electricity for 1 million peopleNo air pollutionTro: Chemistry: A Molecular Approach
20 Nuclear Power Plants - Core fissionable material stored in long tubes, called _______________, arranged in a matrixsubcriticalBtwn fuel rods are ___________________ made of neutron-absorbing materialB and/or Cdneutrons needed to sustain chain reactionrods are placed in a material to slow down ejected neutrons = a _________________allows chain rxtn to occur below critical massTro: Chemistry: A Molecular Approach
21 If the neutron flow in a reactor is carefully regulated Nuclear ReactorsIf the neutron flow in a reactor is carefully regulatedso that only enough heat is released to boil water,then the resulting steamcan be used to produce electricity.
23 PLWR - Core control rods made of n absorbing material. Allows rate of n flow thru reactor to be controlled.Because n’s are required to continue chain rxtn, control rods control the rate of nuclear fissionHotWaterControlRodsFuelRodsColdWaterTro: Chemistry: A Molecular Approach
24 Nuclear ReactorsLight-water reactors:Used to produce electricityFuel rods containing fissile isotope in stabilized form(uranium oxide pellets encased in a corrosion-resistant zirconium alloy)suspended in a cooling bath - transfers heatgenerated by fission rxtn to a 2dary cooling system.
25 Nuclear ReactorsLight-water reactors:Heat generates steam for production of electricity.Control rods absorb n’s & control rate ofnuclear chain rxtn.Pulling control rods out increases n flow,allowing reactor to generate more heat.inserting rods completely stops the rxtn.
27 Heavy-water reactors: Nuclear ReactorsHeavy-water reactors:Deuterium (2H) absorbs n’s less effectively than (1H),but is ~ 2x as effective at scattering neutrons.A nuclear reactor using D2O instead of H2Oas the moderator is so efficient it can use un-enriched uranium as fuel,which reduces operating costs & eliminates need for plants that produce enriched uranium
28 A nuclear fission reactor that produces Nuclear ReactorsBreeder reactors:A nuclear fission reactor that producesmore fissionable fuel than it consumes.Fuel produced is not the same as the fuel consumed.Overall rxtn is conversion of_______________________________which can be isolated chemicallyand used to fuel a new reactor.
29 Concerns about Nuclear Power Core melt-downWaste disposalTransporting wasteHow do we deal with nuclear power plants that are no longer safe to operate?Tro: Chemistry: A Molecular Approach
30 Three Mile Island28 March thru early Aprilof 1979Chernobyl Reactor 1986
31 Japan in 2011In what condition areAmerican Nuclear Reactors?
32 Where Does Energy from Fission Come from? During nuclear fission, some of the mass of the nucleus is converted into energyE = mc2Each mole of U–235 that fissions produces about _________________ J of energya very exothermic chemical reaction produces _______________ J / moleTro: Chemistry: A Molecular Approach
33 Mass Defect & Binding Energy When nucleus forms, some mass of separate nucleons is converted into EDiff in mass btwn separate nucleons & combined nucleus = the mass defectE that is released when nucleus forms = the binding energyTro: Chemistry: A Molecular Approach
35 Calculate mass defect & nuke binding E per nucleon (in MeV) for C–16, radioactive isotope of carbon with a mass of amuGiven:Find:mass C-16 = amu, mass p+ = amu,mass n0 = amumass defect in amu, binding energy per nucleon in MeVConceptual Plan:Relationships:mp+, mn0, mC-16massdefectbinding energySolve:Tro: Chemistry: A Molecular Approach35
37 Calculate the binding E per nucleon in Fe–56 (mass 55.93494 amu) Tro: Chemistry: A Molecular Approach
38 Calculate the binding E per nucleon in Fe–56 (mass 55.93494 amu) Tro: Chemistry: A Molecular Approach
39 Nuclear FusionFusion is combining light nuclei to make heavier, more stable nuclideSun uses fusion of H isotopes to make helium as a power sourceTro: Chemistry: A Molecular Approach
40 Requires high input of E to initiate process need to overcome repulsion of pos nucleiProduces 10x energy per gram as fissionNo radioactive byproductsUnfortunately, only currently working application is the H-bombTro: Chemistry: A Molecular Approach
42 Tokamak Fusion Reactor Tro: Chemistry: A Molecular Approach
43 Making New Elements: Artificial Transmutation High E particles can be smashed into target nuclei, resulting in production of new nucleiTro: Chemistry: A Molecular Approach
44 Rutherford made O–17 bombarding N–14 with alpha rays from radium Particles may be radiation from other radionuclide, or charged particles that are acceleratedRutherford made O–17 bombarding N–14 with alpha rays from radiumCf–244 is made by bombarding U–238 with C–12 in a particle acceleratorTro: Chemistry: A Molecular Approach
45 Artificial Transmutation Bombardment of one nucleus with another causing new atoms to be madecan also bombard with neutronsReaction done in a particle acceleratorTc-97 is made by bombarding Mo-96 with deuterium, releasing a neutronTro: Chemistry: A Molecular Approach
49 CyclotrontargetsourceTro: Chemistry: A Molecular Approach
50 Practice – Predict the other daughter nuclide and write a nuclear equation for each of the following bombarding Ni–60 with a proton to make Co–57bombarding N–14 with a neutron to make C–12bombarding Cf–250 with B–11 producing 4 neutronsTro: Chemistry: A Molecular Approach
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