Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin 1
Lecture 21
Fission and Nuclear Energy
Experimental Nuclear Physics PHYS 741
References and Figures from:- Basdevant, Fundamentals in Nuclear Physics
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Pheno Seminar this Friday
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Friday, November 21st, 2008Phenomenology Seminar
Methods to Detect the Cosmic Neutrino Background
Time: 2:30 pmPlace: 5280 Chamberlin HallSpeaker: Bob McElrath, CERN
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Course Project
Please send me your outline TODAY
Course project outline: aim for 18-20 slides (rule of thumb: 1 slide per 1 min) an outline at beginning of talk is useful show tile for each slide show synopsis of topics for each slide add slide with list of all references
All talks are to be posted by Friday, December 12, 2008, 5pm CST
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Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Energy Release in Fission and Self-Fusion
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- only nuclei with 40 < A < 95 are stable against both fission and self-fusion- Qfis calculated for symmetric fission
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Binding Energies
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at A=120: 8.5 MeV
at A=240: 7.6 MeV
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fission Products
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Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Distribution of Fission Fragments
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asymmetric fission into lighter and heavier nuclei
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fission Fragment Decay
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Cesium-137 and strontium-90 are the most dangerous radioisotopes to the environment in terms of their long-term effects.
Intermediate half-lives of about 30 years suggests that they are not only highly radioactive but that they have a long enough halflife to be around for hundreds of years
Iodine-131 is a major concern in any kind of radiation release from a nuclear accident because it is volatile and because it is highly radioactive, having an 8 day half-life.
Iodine is quickly swept up by the thyroid, so that the total intake of iodine becomes concentrated there.
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Distribution of Fission Fragments
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Mass distributions (or fission-yield curves) for the thermal-neutron fission of uranium-233, uranium-235, and plutonium-239 and the spontaneous fission
of californium
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Energies of Particles in Fission
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Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Nuclear Deformation in Fission
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variation of energy as a function of distortion
EA= fission barrier
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Photo-Fission
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cross-section for 236U -> fission
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fission Products and Neutron Energies
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Mass distribution dependence on the energy excitation in the fission of uranium-235.
At still higher energies, the curve becomes single-humped, with a maximum yield for symmetric mass splits
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fission Fragments and Neutron Yields
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Dependence of neutron yield on initial fragment mass for thermal-neutron fission of uranium-235.
Average number of neutrons emitted by light and heavy fragments are given the symbols L and H; the total from both fragments is . Also shown are the initial (fission fragment) and
final (fission product) mass yields
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fission Threshold Energies & Neutron Separation Energies
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all threshold energies are typically around ~6 MeV
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin 16
thermal n + 235U can lead to fission of 236U
n + 235U has higher energy than lowest fissionable state
on the other hand:thermal n + 238U does not lead to fission, only radiative capture
fission of 239U requires addition of neutron with kinetic energy Tn=6-4.8=1.2 MeV
some nuclei require thermal neutrons for fission, others require fast neutrons
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Cross-Sections as a Function of Neutron Energy
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1.2 MeV threshold for fission
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fissile and Fertile Material
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239Pu and 233U are produced by neutron capture from fertile materials 238U and 232Th.
Nuclei which are used most easily as fuel (fission rapidly by thermal neutron capture)
233U235U239Pu
reactors which burn 239Pu and which contains 238U can produce more Pu than it needs -> breeder reactor
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Configurations for Nuclear Reactors
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natural
typical enrichment
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Moderators
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p = probability for absorption
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Nuclear Reactors
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cooling tower
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Fuel Element for a PWR Reactor
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Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Build-Up of Fission Products
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Gram
ato
mic
weigh
t per
ton
of fu
el
requires 2 n captures on 235-U, varies quadratically with time
single n capture on 238-U, at large times balanced by destruction from fission and n capture
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Production of Trans-Uranium Elements
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n-capture and beta-decays
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Chernobyl
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Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Radioactivity in Spent Fuel
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assume 99.5% of U and Pu was removed for reprocessing
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Oklo Natural Nuclear Reactor
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Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Oklo Natural Nuclear Reactor
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235U is depleted to 0.42% from natural 0.72%
dashed line=Uranium abundance profile
solid line=235U abundance highly depleted
Composition of Uranium Deposit
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Abundances of Nd Isotopes at Oklo
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fission products 143-150Nd all have larger than normal abundances compared to 142Nd
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin
Radiative Neutron Capture Cross-Section on 149Sm
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first resonant state can absorb thermal neutrons (3kT = 0.078 eV, T = 300K)
Experimental Nuclear Physics - PHYS741Karsten Heeger, Univ. Wisconsin 31
