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Nuclear Fission energy for war and peace

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Nuclear Fission energy for war and peace Nuclear fission is a process, by which a heavy nuclide splits into two or more pieces Nuclear fission reactions release a lot ... – PowerPoint PPT presentation

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Title: Nuclear Fission energy for war and peace


1
Nuclear Fission energy for war and peace
Nuclear fission is a process, by which a heavy
nuclide splits into two or more pieces Nuclear
fission reactions release a lot of
energy. Nuclear energy has been used for peace
and for war.
2
Discovery of Induced Nuclear Fission
O. Hahn, L. Meitner, and F. Strassmann in
Berlin F. Joliot and I. Curie in Paris
Enrico Fermi in Rome
All three groups thought the reactions to
be 238U (n, ?) 239U92 (, ?) 239E93 (, ?) 239E94
3
Discovery of Induced Nuclear Fission
Hahn (chemist), Meitner (physicist), and F.
Strassmann (analytical chemist) used H2S to
precipitate the radioactive products. The
half-life measurements indicated to them that not
one but many elements were produced.
Meitner used barium ions, Ba2, as a carrier and
precipitated the radioactive products from the
neutron bombardment.
4
Discovery of Induced Nuclear Fission
Atomic weight of Ba2 is 137
Neutron induced uranium nuclear fission reactions
5
Induced Nuclear Fission
A simplified view of neutron induced fission n
235U ? xxxEyy uuuEww 3 n
6
Discovery of Induced Nuclear Fission
The Official History of the Manhattan
Project Dr. Meitner brought the discovery of
neutron induced fission to Copenhagen as she, a
non-Aryan, exiled from Germany in 1938. She told
Frisch, who told N. Bohr and Bohr told Fermi
Fermi fond out only 235U underwent fission, for
example 235U n ? 142Cs55 90Rb37
4n neutrons are releases
7
Nuclear Fission Energy
Fission Energy
8
Nuclear Fission Energy
Problem If a 235U atom splits up into two
nuclides with mass number 117 and 118, estimate
the energy released in the process.
9
Nuclear Fission Energy
If a 235U atom splits up into two nuclides with
mass number 117 and 118, estimate the energy
released in the process.
From handbooks Stable nuclides with mass numbers
117 and 118 are 117Sn50, and 118Sn50 and masses
are given below the symbols 235U ?
117Sn50 118Sn50 235.043924
116.902956 117.901609 Qfe Qfe 0.2394 amu
(931.5 MeV) / (1 amu) 223 MeV.
Discussion The fission reaction equation is over
simplified. Usually, neutrons are released too.
10
Nuclear Fission Energy
Assume the neutron induced fission reaction to
be, 235U n ? 142Cs55 90Rb35 4 n.
explain the results and estimate the energy
released.
Solution The neutron-rich fission products are
beta emitters 142Cs ? 142Ba ? (1
min) 90Rb ? 90Sr? ? (half-life, 15.4 min) 142Ba
? 142La ? (11 min) 90Sr ? 90Y ? (27.7
y) 142La ? 142Ce ? (58 min) 90Y ? 90Zr
(stable) ? (64 h) 142Ce ? 142Pr ?
(5?1015 y) 142Pr ? 142Nd (stable) ? (19 h)
11
Nuclear Fission Energy cont.
Assume the neutron induced fission reaction to
be, 235U n 142Cs55 90Rb35 4 n.
explain the results and estimate the energy
released.
Solution cont. For the energy, consider the
reaction and mass balance 235U92 ?
142Nd60 90Zr40 3 n
Q 235.04924 141.907719 89.904703 3x1.008665
Q Q (235.043924 - 141.907719 - 89.904703 -
3x1.008665) 0.205503 amu (931.4812 MeV/1
amu) 191.4 MeV per fission(1.6022e-13 J /
1 MeV) 3.15e-11 J
12
Nuclear Fission Energy
Estimate the energy released by the fission of
1.0 kg of 235U.
Solution From the results of the previous two
examples, energy released by 1.0 kg uranium-235
is estimated below (3.15e-11 J) 1000
g 8.06e13 J (per kg).
1 mol 235 g
6.023e23 1 mol
Discussion This is a large amount of energy, and
it is equivalent to the energy produced by
burning tones of coal or oil.
13
Nuclear Fission Energy
Energy (MeV) distribution in fission reactions
Kinetic energy of fission fragments Prompt (lt
106 s) gamma (?) ray energy Kinetic energy of
fission neutrons Gamma (?) ray energy from
fission products Beta (?) decay energy of fission
products Energy as antineutrinos (ve)
167 MeV 8 8 7 7 7
14
The Cyclotron and Fission Research
Particle accelerators machines to speed up
particles Linear accelerators Cyclotrons
15
The Cyclotron and Fission Research
7Li (p, n) 7Be 3T (p, n) 3He 1H (t, n) 3He 2D (d,
n) 3He 2D (t, n) 4He 3T (d, n) 4He
Fusion reactions studied using the cyclotron
16
The Cyclotron and Fission Research
Threshold Energy range (keV) Reaction energy(
keV) narrow-energy neutron 51V (p, n)
51Cr 2909 5.6-52 45Sc (p, n) 45Ti 1564
2.36-786 57Fe (p, n) 57Co 1648
2-1425 __________________________________ The
threshold energy is the minimum energy of
proton required for the reaction.
Neutrons of desirable energy is required for
fission research.
17
The Cyclotron and Fission Research
For neutron sources from the cyclotron, energy
can be varied. Energy dependence of neutron
induced fission studied. The cross section data
enabled nuclear reactor design.
fast neutrons - 10 MeV to 10 KeV) slow neutrons
- 0.03 to 0.001 eV for neutron induced
fission
18
The Synthesis of Plutonium
Short notations 238U (n, ?) 239U ( , ?) 239Np ( ,
?) 239Pu or 238U (n, 2?) 239Pu
Fast neutrons provided the reactions 238U n ?
239U ? 239U ? 239Np ? (t1/2 23.5
min) (t1/2 2.35 d) 239Np ? 239Pu ?
19
(No Transcript)
20
Uniting Political and Nuclear Power
Neutron induced fission reactions release energy
and neutrons, thus it is possible to start a
chain reaction for nuclear power. Dictator Hitler
(political power in 1933) made many scientists in
Austria, Hungary, Italy and Germany uncomfortable
and they came to the U.S.A. Hitler invaded
Poland, Hungary, Slovak and other European
countries. Nuclear fission was discovered in
Germany, and nuclear power threatens the
world. Leo Szilard, Eugene Wigner, and Edward
Teller drafted a letter and Einstein signed the
letter for president Roosevelt of U.S. to use
political power for nuclear power.
21
Uniting Political and Nuclear Power
F.D. Roosevelt (Einsteins address omitted) .
. . . . . . (address omitted) Sir Some recent
work by E.Fermi and L. Szilard, which has been
communicated to me in manuscript, leads me to
expect that the element uranium may be turned
into a new and important source of energy in the
immediate future. Certain aspects of the
situation which has arisen seem to call for
watchfulness and, if necessary, quick action on
the partof the Administration. I believe
therefore that it is my duty to bring to your
attention the following facts and
recommendations . . . . (middle part
omitted) . . . . I understand that Germany
has actually stopped the sale of uranium from the
Czechoslovakian mines which she has taken over.
That she should have taken such early action
might perhaps be understood on the ground that
the son of the German Under-Secretary of State,
von Weizsäcker, is attached to the
Kaiser-Wilhelm-Institut in Berlin where some of
the American work on uranium is now being
repeated. Yours very truly,
22
Thermal Neutrons
Experiment Neutron bombarded samples surrounded
by water, wood, and paraffin are more radioactive
- Fermis group discovered
Conclusion Slow neutrons (0.03 to 0.001 eV) are
more effective for inducing fission of 235U Fast
neutrons (10 MeV to 10 KeV) favours neutron
capture reaction of 238U Light atoms are
effective moderators
23
Thermal Neutrons - Moderators
Light atoms are effective moderators
24
Thermal Neutrons Cross Sections
Cross section (?) a measure of reaction
probability Thermal neutron cross sections
(?c) Thermal neutron cross section for fission
(?f)
1H 2H 12C 14N 16O 113Cd ? c
/b 0.33 0.00052 0.0034 1.82 0.0002 19,820
Moderators H2O vs. D2O vs. C Fermis avoided N2
in his first nuclear reactor and used Cd for
emergency
25
Thermal Neutrons Cross Sections
Uranium for Fission Fuel in Nuclear Reactor
113Cd 233U 235U 238U ? c /b 19,820 46
98 2.7 ?f /b 530 580 2.710-6 t1/2/y 1
.6105 7108 4.5109
26
Thermal Neutrons Cross Sections
Plutonium Isotopes 236Pu 237Pu 238Pu 239Pu
240Pu 241Pu 242Pu ?f 150 2100 17 742 0.08
1010 0.2 t1/2 2.9y 45 d 88 y 24131y 6570 y
14y 3.8105y
Neutrons Capture Cross Sections of Cadmium
Isotopes 106Cd 108Cd 110Cd 111Cd 112Cd 113Cd 11
4Cd ? c / b 1 1 0.1 24 2.2 19,820 0.3
Abundance/ 1.25 0.89 12.45 12.80 24.13 12.22 28.
37
27
Fission Products nuclides produced in nuclear
fission
Data on fission products are required for reactor
design, operation, and accident responses. The
study of fission products requires the
separation, identification, and quantitative
determination of various elements and isotopes.
Fission products emit ? particles until they are
stable. Mass number range 40 - 170 Elements
range all the elements in the 4th, 5th, and 6th
periods. including the lanthanides.
28
Fission Products
Fission yield is the relative amounts of nuclides
formed in fission reactions. The fission yield
curve shown here shows most fission reactions
split fission atoms into two unequal fragments.
29
Nuclear Fission Products
Fission-product and their decay data are needed
for social and environmental concerns, and for
the management of used fuel. Fission nuclides
usually have very short half lives. Typical
medium-life fission products 85K 10.7 y, 90Sr
29 y, 137Cs 30 y, Typical long-life fission
products 126Sn 1.0e5 y, 126Tc 2.1e5 y,
91Tc 1.9e6 y, 135Cs 3.0e6 y, 107Pd 6.5e6 y, and
129Tc 1.6e7 y.
Xenon poisoning 115Xe, ?c 2,640,000 b, and
t1/2 9.2 h
30
First Fission Nuclear Reactor
Fermis group assembled natural uranium into an
atomic pile to test the feasibility of a
sustained chain fission reaction. Key elements
fuel, neutron moderator, control rod, neutron
detector, and radioactivity detector Dec. 2,
1942, Fermi achieved sustained chain reaction,
and the first fission reactor provided data for
future design of nuclear reactors.
Today, more than 400 power nuclear reactors
provided energy world wide, more than 100 of them
in the US.
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