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Nuclear Reactions. Fission and Fusion. A brief history…. 1919: Ernest Rutherford experimented with bombarding nitrogen gas molecules with alpha particles emitted from bismuth-214 Discovery: faster moving particles were produced, and these could travel farther than the alpha particles! - PowerPoint PPT Presentation


  • Nuclear ReactionsFission and Fusion

  • A brief history1919: Ernest Rutherford experimented with bombarding nitrogen gas molecules with alpha particles emitted from bismuth-214Discovery: faster moving particles were produced, and these could travel farther than the alpha particles!New particles also deflected in a magnetic field like a positive particle

  • A brief historyConclusion: The faster moving particles were protonsArtificial Transmutation:The change of one element to another through the bombardment of a nucleus

    More experiments to determine exact nature of the particles and how they were created done with a cloud chamber

  • Cloud ChambersInvented ~1911 by a Scottish Atmospheric Physicist (C.T.R. Wilson) to experiment with rain clouds.Enclosed environment made to be supersaturated (originally with water vapor, now commonly ethanol)Ions introduced to this environment would attract water molecules (which are polar), forming cloudsEarned a share in the 1927 Nobel Prize in Physics for the invention

  • Cloud ChambersWhy would this be useful for Rutherford?Water vapor condenses around ionsAn alpha particle is ionizing radiation, thus leave a LOT of ions in its pathWater vapor would condense around these ions, leaving a vapor trail showing where an alpha particle had beenVideo

  • Rutherfords TheoriesIf proton was simply chipped off the Nitrogen nucleus by the alpha particle, there should be 4 visible tracks in the cloud chamber:The original alpha particle BEFORE collisionThe alpha particle AFTER the collisionThe chipped off protonThe Nitrogen nucleus, now charged, as it recoiled after the collision

  • Rutherfords TheoriesIf alpha particle was absorbed, and that caused the proton to be pushed out, then there should be 3 visible tracks:The alpha particle before collisionThe proton emitted after the collisionThe path of the recoiling Nitrogen nucleusThis theory was supported in 1925

  • Balancing Nuclear Equations:Note: Deuteron = Hydrogen-2 atom, a.k.a DeuteriumExample problem:A sample of Oxygen-16 is bombarded with neutrons. If one of the resulting products is a deuteron, what is the resulting nucleus?

  • Unified Mass Unit (u)A unit adopted by scientists that is more appropriate for masses along the order of magnitude of atomic masses1 u = 1.66 x 10-27 kgMass of an electron (me) = 0.000549 uMass of a proton (mp) = 1.007277 uMass of a neutron (mn) = 1.008665 uMass of 1 H atom (mH) = 1.007825 u

  • Mass-energy equivalenceEinstein hypothesized a relationship between mass and energy in 1905Many years later, data from nuclear reactions showed that his hypothesis was indeed true

    c = 3.00 x 108 ms-1m = mass (kg)E = Energy (J)

  • Mass-energy equivalence

    Used to calculate the Rest Energy of a massUsed to calculate the amount of energy released in nuclear reactionsFor Example:Calculate the amount of energy released when 1.00 kg of fuel is used up in a nuclear reactor

  • The unified mass unit is defined asthe mass of one neutral atom of Carbon-121/12 of the mass of one neutral atom of Carbon-121/6 of the mass of one neutral atom of Carbon-12The mass of the nucleus of Carbon-12

  • Binding EnergyAll atomic nuclei have a total mass that is lower than the sum of the masses of each individual particleFor example: The EXPECTED mass of an atom of Helium would be the sum of the mass of 2 neutrons, 2 protons, and 2 electrons:2(0.000549 u) + 2(1.007277 u) + 2(1.008665 u) = 4.032982 uThe MEASURED mass of an atom of helium has been found to be 4.002602 ua difference of 0.03038 uThis difference is known as the Mass Defect of the atom

  • Binding Energya measure of the energy needed to keep a nucleus together Binding Energy is the energy equivalent of the mass defectE = mc2E = (1.66 x 10-27 kg)(3.00 x 108 ms-1)2E = 1.49 x 10-10 J = 931 MeV(Since 1 eV = 1.6 x 10-19 J)

  • What is the energy equivalent of 1 u?319 MeV931 eV319 keV931 MeV

  • Binding Energy Example:Calculate the binding energy of Oxygen-16. The measured mass of Oxygen-16 is 15.994915 u8 electrons+8 protons+8 neutrons

    8me + 8mp + 8mn = mexpected= 8(0.000549 u) + 8(1.007277 u) + 8(1.008665 u)= 0.004392 u + 8.058216 u + 8.069320 u= 16.131928 u

  • Binding Energy Example:Calculate the binding energy of Oxygen-16. The measured mass of Oxygen-16 is 15.994915 umdefect = mexpected mmeasured= 16.131928 u 15.994915 u= 0.137013 u

    Eb = mdefect (931 MeVu-1)Eb = (0.137013)(931)= 128 MeV

  • How many Joules of energy is 128 MeV?8.00 x 1020 J8.00 x 1026 J2.05 x 10-17 J2.05 x 10-11 J

  • Nuclear ReactionsFission: A reaction that involves the splitting of a large, unstable nucleus into 2 or more smaller, more stable nuclei

  • Which nucleus is most likely to be part of a fission reaction?Carbon-14DeuteriumPlutoniumPotassium-40

  • Nuclear Reactions

    Fusion: A reaction that joins two very light nuclei to form a heavier nucleus

    Picture source:

  • Nuclear Reactions and Binding EnergyNuclei with higher amounts of binding energy per nucleon are more stable than those with lower amounts of binding energy per nucleon.Fission and fusion processes each release large amounts of energy as the nuclei join or split to form more stable products.To predict how much energy can result from a nuclear reaction, we use a binding energy curve

  • Binding Energy Curve

  • Binding Energy CurveExample: Use the binding energy curve to predict the amount of energy released when Uranium-235 undergoes fission to produce two Palladium-117 fragments.Eb for 235U = 7.6 MeV/nucleonEb for 117Pd = 8.4 MeV/nucleonThe difference between these values, multiplied by the total number of nucleons, is equal to the amount of energy released in the reaction:(0.8 MeV/nucleon) x (235 Nucleons) = 188 MeV

  • Nuclear FissionOnly takes place in certain very heavy elements, such as Uranium-235Fissile Uranium-235 is used in nuclear reactions:Nucleus bombarded with a neutron to begin a chain reaction

  • Fission ReactionsSelf-sustaining (chain) reactions: when enough neutrons are produced to naturally enable the reaction to continue until all fissile material is goneExamples: Nuclear Reactors in Power Plants; Bombs dropped on Hiroshima and Nagasaki in WWIICritical Mass: The amount of fissile material required to sustain a fission reaction

  • Figure from Physics for Scientists and Engineers (6th ed.) by Serway and Jewett (Thomson Brooks/Cole, 2004).

  • Nuclear Fusion ReactionsConditions required for fusion reactions:Very high temperatures (because nuclei need very high kinetic energies)Very densely packed (to ensure that enough collisions will occur), therefore:Very high pressuresProblems with creating fusion on Earth:Containment is a huge problemAt temps required, atoms would ionize and technically would become a plasma

  • Nuclear Fusion ReactionsProton-Proton Cycle = the fusion reaction that is the source of energy in young/cool stars such as the sun:

    The first two reactions in the cycle must occur twiceTotal energy released = 24.7 MeV

  • Fusion ExampleCalculate the energy released when a proton and a deuteron undergo fusion to produce helium-3.


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