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Fission

Fission. Neutrons are like neutral protons. Mass is 1% larger No coulomb force Neutron lifetime is long, but eventually decays to a proton. l = 624 s. Neutrons can interact directly with nuclei. Strong nuclear force Neutron capture reactions usually involve gamma ray emission. Neutrons.

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Fission

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  1. Fission

  2. Neutrons are like neutral protons. Mass is 1% larger No coulomb force Neutron lifetime is long, but eventually decays to a proton. l= 624 s Neutrons can interact directly with nuclei. Strong nuclear force Neutron capture reactions usually involve gamma ray emission. Neutrons

  3. Neutrons in nuclear reactions have distinct ranges of energy. Slow or thermal neutrons with energies under 1 eV Fast neutrons with energies from 100 keV to 10 MeV Relativistic neutrons with energies over 1 GeV Useful Fact What is the kinetic energy of a thermal neutron? It must be about kT. At 20 °C, kT = 1/40 eV Better is (3/2)kT 3 degrees of freedom K = 0.038 eV Neutron Energies

  4. Heavy nuclei have higher rest masses than two lighter nuclei. Binding energy U-235: -7.2 MeV/nucleon Daughters: -8.5 MeV/nucleon The binding energy difference is released when heavy nuclei split. Requires quantum tunneling Ejects excess neutrons Fission is made more likely after neutron capture. Mass Defect 100Mo 132Sn 235U

  5. The energy released energy from uranium fission can heat water. The heated water can drive a steam turbine and electric generator. This is the basis for nuclear power plants. Nuclear Reactor World Nuclear Association

  6. Nuclear fission of 235U produces multiple neutrons per reaction. Neutron energy is important to reaction. 235U uses thermal neutrons 238U absorbs fast neutrons Neutrons sustain the reaction. Moderators slow down fast neutrons Absorbers capture neutrons Typical fission: Releases 208 MeV Chain Reaction

  7. Fission is exothermic. Excess energy available in reaction Uranium fission produces neutrons. Needed for chain reaction An uncontrolled chain reaction creates a nuclear explosion. Nuclear Bomb next Hiroshima 1945

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