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Download Nuclear fission and fusion Types of decay process Types of decay process Rates of decay Rates of decay Nuclear stability Nuclear stability Energy changes

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  • Slide 1
  • Nuclear fission and fusion Types of decay process Types of decay process Rates of decay Rates of decay Nuclear stability Nuclear stability Energy changes Energy changes Fission and fusion Fission and fusion
  • Slide 2
  • Forces at work in the nucleus Electrostatic repulsion: pushes protons apart Electrostatic repulsion: pushes protons apart Strong nuclear force: pulls protons together Strong nuclear force: pulls protons together Nuclear force is much shorter range: protons must be close together Nuclear force is much shorter range: protons must be close together
  • Slide 3
  • Neutrons only experience the strong nuclear force Proton pair experiences both forces Proton pair experiences both forces Neutrons experience only the strong nuclear force Neutrons experience only the strong nuclear force But: neutrons alone are unstable But: neutrons alone are unstable
  • Slide 4
  • Neutrons act like nuclear glue Helium nucleus contains 2 protons and 2 neutrons increase attractive forces Helium nucleus contains 2 protons and 2 neutrons increase attractive forces Overall nucleus is stable Overall nucleus is stable
  • Slide 5
  • As nuclear size increases, electrostatic repulsion builds up There are electrostatic repulsions between protons that dont have attractive forces There are electrostatic repulsions between protons that dont have attractive forces More neutrons required More neutrons required Long range repulsive force with no compensation from attraction
  • Slide 6
  • Neutron to proton ratio increases with atomic number Upper limit of stability
  • Slide 7
  • Upper limit to nuclear stability Beyond atomic number 83, all nuclei are unstable and decay via radioactivity Beyond atomic number 83, all nuclei are unstable and decay via radioactivity Radioactive decay (Transmutation) formation of new element Radioactive decay (Transmutation) formation of new element Atomic number decreases Alpha particle emitted Mass number Atomic number
  • Slide 8
  • Odds and sods All elements have a radioactive isotope All elements have a radioactive isotope Only H has fewer neutrons than protons Only H has fewer neutrons than protons The neutron:proton ratio increases with Z The neutron:proton ratio increases with Z All isotopes heavier than bismuth-209 are radioactive All isotopes heavier than bismuth-209 are radioactive Most nonradioactive isotopes contain an even number of neutrons (207 out of 264). 156 have even protons and neutrons; 51 have even protons and odd neutrons; 4 have odd protons and neutrons Most nonradioactive isotopes contain an even number of neutrons (207 out of 264). 156 have even protons and neutrons; 51 have even protons and odd neutrons; 4 have odd protons and neutrons
  • Slide 9
  • Nuclear processes relieve instability Chemical reactions involve electrons; nuclear reactions involve the nucleus Chemical reactions involve electrons; nuclear reactions involve the nucleus Isotopes behave the same in chemical reactions but differently in nuclear ones Isotopes behave the same in chemical reactions but differently in nuclear ones Rate of nuclear process independent of T,P, catalyst Rate of nuclear process independent of T,P, catalyst Nuclear process independent of state of the atom element, compound Nuclear process independent of state of the atom element, compound Energy changes are massive Energy changes are massive
  • Slide 10
  • Types of radiation
  • Slide 11
  • Alpha particle emission 92 protons 146 neutrons 238 nucleons 2 protons 2 neutrons 4 nucleons 90 protons 144 neutrons 234 nucleons
  • Slide 12
  • Beta particle emission 53 protons 78 neutrons 131 nucleons 54 protons 77 neutrons 131 nucleons 0 nucleons -1 charge
  • Slide 13
  • Other decay processes Positron emission: the conversion of a proton into a neutron plus positive electron Positron emission: the conversion of a proton into a neutron plus positive electron Decrease in z with no decrease in m Decrease in z with no decrease in m Electron capture: the capture of an electron by a proton to create a neutron Electron capture: the capture of an electron by a proton to create a neutron Decrease in z with no decrease in m Decrease in z with no decrease in m 19 protons 21 neutrons 40 nucleons 18 protons 22 neutrons 40 nucleons 0 nucleons +1 charge 80 protons 117 neutrons 197 nucleons 79 protons 118 neutrons 197 nucleons 0 nucleons -1 charge
  • Slide 14
  • ProcessSymbol Change in atomic number Change in mass number Change in neutron number Alpha-2-4-2 Beta ----+10 Gamma000 Positron ++++0+1 Electron capture E.C.0+1 Summary of processes and notation
  • Slide 15
  • Measuring decay Rates of radioactive decay vary enormously from fractions of a second to billions of years Rates of radioactive decay vary enormously from fractions of a second to billions of years The rate equation is the same first order process The rate equation is the same first order process Rate = k x N
  • Slide 16
  • Half-life measures rate of decay Concentration of nuclide is halved after the same time interval regardless of the initial amount Half-life Concentration of nuclide is halved after the same time interval regardless of the initial amount Half-life Can range from fractions of a second to millions of years Can range from fractions of a second to millions of years
  • Slide 17
  • Mathematical jiggery pokery Calculating half life from decay rate Calculating half life from decay rate t = 0, N = N o ; t = t 1/2, N = N o /2 Calculating residual amounts from half life Calculating residual amounts from half life
  • Slide 18
  • Magic numbers Certain numbers of protons and/or neutrons convey unusual stability on the nucleus Certain numbers of protons and/or neutrons convey unusual stability on the nucleus 2, 8, 20, 28, 50, 82, 126 There are ten isotopes of Sn (Z=50); but only two of In (Z=49) and Sb (Z=51) There are ten isotopes of Sn (Z=50); but only two of In (Z=49) and Sb (Z=51) Magic numbers are associated with the nuclear structure, which is analogous to the electronic structure of atoms Magic numbers are associated with the nuclear structure, which is analogous to the electronic structure of atoms
  • Slide 19
  • Correlation of neutron:proton ratio and decay process
  • Slide 20
  • Stability is not achieved in one step: products also decay Here atomic number actually increases, but serves to reduce the neutron:proton ratio Here atomic number actually increases, but serves to reduce the neutron:proton ratio Beta particle emission occurs with neutron-excess nuclei Beta particle emission occurs with neutron-excess nuclei Alpha particle emission occurs with proton-heavy nuclei Alpha particle emission occurs with proton-heavy nuclei
  • Slide 21
  • Radioactive series are complex The decay series from uranium-238 to lead-206. Each nuclide except for the last is radioactive and undergoes nuclear decay. The left-pointing, longer arrows (red) represent alpha emissions, and the right-pointing, shorter arrows (blue) represent beta emissions.
  • Slide 22
  • Energy changes and nuclear decay In principle there will be an energy associated with the binding of nuclear particles to form a nucleus In principle there will be an energy associated with the binding of nuclear particles to form a nucleus Experimentally demanding! Experimentally demanding!
  • Slide 23
  • Use Einsteins relationship E = mc 2 Consider the He nucleus: Consider the He nucleus: Mass of individual particles = 4.03188 amu Mass of He nucleus = 4.00150 amu Mass loss = 0.03038 amu The lost mass is converted into energy the binding energy, which is released during the nuclear process The lost mass is converted into energy the binding energy, which is released during the nuclear process For the example above, the energy is 2.73 x 10 9 kJ/mol For the example above, the energy is 2.73 x 10 9 kJ/mol
  • Slide 24
  • Inter-changeability of mass and energy Loss in mass equals energy given out Loss in mass equals energy given out E = mc 2 Tiny amount of matter produces masses of energy: Tiny amount of matter produces masses of energy: 1 gram 10 14 J Energy and mass are conserved, but can be inter- changed Energy and mass are conserved, but can be inter- changed Binding energy per nucleon presents the total binding energy as calculated previously per nuclear particle Binding energy per nucleon presents the total binding energy as calculated previously per nuclear particle Usually cited in eV, where 1 eV = 1.6x10 -19 J Usually cited in eV, where 1 eV = 1.6x10 -19 J
  • Slide 25
  • Average mass per nucleon varies with atomic number H He Fe U Nucleon mass The binding energy per nucleon for the most stable isotope of each naturally occurring element. Binding energy reaches a maximum of 8.79 MeV/nucleon at 56Fe. As a result, there is an increase in stability when much lighter elements fuse together to yield heavier elements up to 56Fe and when much heavier elements split apart to yield lighter elements down to 56Fe, as indicated by the arrows.
  • Slide 26
  • Mass changes in chemical reactions? Conservation of mass and energy means that energy changes in chemical processes involve concomitant changes in mass Conservation of mass and energy means that energy changes in chemical processes invo

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