N uclear fusion and Radioactivity
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Nuclear fusion and Radioactivity
PDP Physics
Image: http://en.wikipedia.org/wiki/Exoplanet
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GENERATING ELECTRICITY
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Electricity generation
• wind• hydroelectric• coal• oil• natural gas• biofuel• solar power• geothermal• (nuclear)
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Electricity generation presentation• in a group of 2 or 3• on google drive or prezi• about 3-4 minutes
Your presentation should answer the following:• How does it work?• What energy conversions are involved?• How efficient is it?• How much power does a typical plant produce?• How much power is generated in total in Sweden?• Where do the resources originate?• What are the benefits of this method of
generating electricity?• What are the problems? How significant are they?• What is the future potential?
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Electricity bill in kWh
http://www.dolceta.eu/sverige/Mod6/Elrakningen.html
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kiloWatthours are units of energy
1kWh = 1kW used for 1 hourEnergy = power × time1kWh ≈ 4MJ
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Comparing different energy uses
Fluctuations kWh per daykWh/d is a unit of powerpower = energy/time
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Energy density of a fuel
energy density = energy released mass of fuel
energy density in MJ/kgUranium 79 500 000MJ/kgCoal 24MJ/kg
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Efficiency
What percentage of the energy comes out as useful energy?
efficiency = energy out × 100 energy in
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WHAT IS NUCLEAR FUSION?
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WHAT ARE ATOMS BUILT FROM?
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Atoms
• atomic number• mass number• relative atomic mass• electron shell• isotope• atomic mass unit, u• elementary charge, e• electronVolt, eV
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Atomic structure
7
Li3
Atomic number, Z
Mass number, A
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Atomic nucleus
Strong nuclear force (protons and neutrons)
Electrostatic force (protons and electrons)
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Subatomic particlesProton Electron Neutron
Charge, e +1 -1 0
Mass, u 1.007 0.00548 1.009
Location in atom nucleus shells nucleus
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ELEMENTARY PARTICLES
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An elementary particle has no internal structure and is not made
from smaller constituents.A composite particle is made from
elementary particles.
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Particles are made of particles
A proton is built from 3 quarks
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composite:atom
protonneutron
elementary:electron
quarkneutrino
proton
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RADIOACTIVITY
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Ionizing radiation
consists of
mass charge penetrating power
α alpha
β- beta
γ gamma
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Background radiation
• is the natural radiation from materials in the environment including rocks, the air and living organisms
• varies with location
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What is the relationship between Z and N?
• Research the stable isotopes of as many atoms as possible and plot a graph of N against Z
• Plot a trendline and write down the gradient. Explain what the gradient means for this graph.
• Explain why this pattern occurs using ideas about the strong nuclear force and the electrostatic force.
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Nuclear Radiation
Stable or unstable?
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Geiger-Müller tube (GM tube)
Image: http://en.wikipedia.org/wiki/Geiger_counter
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Nuclear symbols
The nucleus of an atom can be represented as:
AZX
• A is the atomic mass (number of protons + neutrons)• Z is the atomic number (number of protons- see
Periodic Table)• X is chemical symbol (see Periodic Table)
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Alpha decay
21986Rn 215
84Po + 42α
Z decreases by 2A decreases by 4
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Write nuclear decay equations for the alpha decay of:
Polonium-218Gold-196
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Beta decay
146C 14
7N + 0-1β + 0
0ν
Z increases by oneA constant
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Write nuclear decay equations for the beta decay of:
Phosphorous-32Iodine-131
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Radioactivity
α-decay
β-decay
γ decay
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Decay series
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HOW LONG DOES IT TAKE AN UNSTABLE ATOM TO DECAY?
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Half lifeThe time it takes for the number of nuclei of the isotope in a sample to halveorThe time it takes for the count rate from a sample containing the isotope to fall to half its starting level
Images: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atoms_radiation/nuclearradiationrev7.shtml
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Half life
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Activity
• The activity of a sample, A, is the number of decays in one second.
• The decay constant, λ, is the probability that a single nucleus will decay in one second.
• N is the total number of unstable nuclei
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Radioactive decay law
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ARTIFICIAL TRANSMUTATION
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Artificial transmutations
• a nucleus can ‘capture’ another particle• this is the only way to speed up radioactive
decay
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NUCLEAR BINDING ENERGY
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Bang! Trinity test
• plutonium fission• 84 TeraJoules = 20 kton TNT
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Bang! first H bomb test in 1952
• hydrogen fusion• 44 PetaJoules = 10 Mtons of TNT
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Nuclear fission
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Nuclear fusion
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unified atomic mass unit
1u is 1/12 of the mass of a carbon-12 atom
mp = 1.007276u
mn = 1.008665u
me = 0.0005486u
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Atoms are lighter than the nucleons which they are built from
the mass defect, δ is the difference between the total mass of the individual nucleons and the mass of the atomic nucleus
mass defect of HeliummHe = 4.0026u
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Binding energybinding energy of the nucleus is the energy needed to separate the nucleons
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How much energy is released when a helium nucleus is formed?
• mp = 1.00728u• mn = 1.00866• mass of 42He nucleus = 4.00153u• 1u = 1.66054 x 10-27kg = 931.494MeVc-2
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Atoms are lighter than the nucleons which they are built from
the mass defect, δ
mass from n and p energy released as nucleus is
made
Tsokos p.387qn1
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binding energy per nucleon
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Fission and fusion
How does the curve of binding energy per nucleon explain why fission of heavy elements releases energy, while fusion of light elements releases energy?
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NUCLEAR FISSION
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Nuclear Fission
• a nuclear chain reaction sustained by neutrons1
0n + 23592U 141
56Ba + 9236Kr + 31
0n
a. What is the mass change?b. How much energy is released per nucleus in Joules?c. How much energy in Joules is released by 1g of Uranium enriched to 3% U-235?U-235 = 235.04392u neutron = 1.0086Ba-141 = 140.91441u Kr-92 = 91.92615u
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The fission of one atom of U-235 generates 202.5 MeV
= 3.244 × 10−11 Jequivalent to 19.54 TJ/mol
= 83.14 TJ/kg
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Designing a nuclear reactor: maintaining
the reaction• enrichment• size of fuel block• speed of neutrons
moderator- slows neutronscontrol rods- absorb neutronsheat exchanger- transfer heat
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Reactor core
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Nuclear power plantAdvantages:high energy densityhuge reserves of U
Disadvantages:radioactive wasteAccident riskProliferationNon-renewable
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Nuclear waste: mix of isotopes with short and long half lives
spent fuel in a storage pondunderground storage
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Production of Plutonium-239
23892U + 1
0n 23992U
23992U 239
93Np + 0-1β + 0
0ν239
93Np 23994Pu + 0
-1β + 00ν
plutonium is toxic, but can be reprocessed and used in a fast breeder reactor (or for a fission bomb)
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NUCLEAR FUSION
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Nuclear Fusion Reaction
21H + 3
1H 42He + 1
0n
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How much energy is released in nuclear fusion?
Deuterium 2.01410uHydrogen 1.00783uHelium-4 4.00260uneutron 1.0086u
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Nuclear binding energy
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Fusion reactors
Benefits• Very high energy density• Large resources of fuel in seawater• Less radioactive wasteProblems• Complex technology• Not currently viable• Waste
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Joint European Torus10MW for 0.5s (50% of input power)
3m radius3.45T magnetic fieldcurrent 3MA
ITER
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Teaching notes