Final Exam
• Wed 3/18 from8:00am-11:00 WLH 2005
• Will cover all the course material including
the last week
• 25 questions –multiple choice.
• You are allowed to bring 1sheet of paper
with equations on both sides.
• Bring a scantron form and a picture id.
Nuclear energy
Nuclear Fission
Nuclear Fusion
Energy consumptions vs
gross national product
Oil Production in the US has peaked
Energy Use USA
World production is close to peaking
1
World Oil Resources
Alternatives to oil
Coal
Nuclear Energy
Fission
Fusion
Hydroelectric
Wind
Solar
Biomass
Curve of the Binding Energy
fission
Natural radioactivity
Many elements found in nature are unstable and decay
emitting radioactivity.
fusion
These include Uranium, 238U , Radon
and Potassium 40K. Carbon 14C,
224Ra
The half lives of natural radio-isotopes are long.
Not useful as sources for power.
Low Power output.
Energy can be released by Fusion and Fission
Induced Nuclear reactions
Fission of Uranium
Can result in short half lives- fast reactions-high energy density
Fermi (1936)
Combining nuclei (Fusion)
D + 21D ⎯⎯
→ 31T + 11H
2
1
Fast
neutrons
+ Energy
Slow
neutrons
Bombard uranium with
neutrons
Found induced radioactivity
Neutron reactions (Fission)
n+
1
0
235
92
U ⎯⎯
→ 141
56 Ba +
92
36
Kr + 3 01n + Energy
Neutron
Source
(radon+Be)
parafilm
uranium “Transuranium elements”
2
Fission of Uranium
Liquid Drop model-
Strassman and Hahn (1939)
Irradiated Uranium with neutrons
Detected Barium
Conclude Uranium nuclei splits into smaller fragments
n+
1
0
235
92
U ⎯⎯
→ 141
56 Ba + other _ products
Nuclear Chain reaction
Explained fission due to the instability
of the higher larger nucleus.
Lise Meitner
T1/2 ~10-12 s
n+
1
0
235
92
U ⎯⎯
→
236
92
U ⎯⎯
→
Ba + products
Critical Condition
235U
(Fission)
n
n
n
(Escape)
235U
n
238U (Capture)
Nuclear reactor
Chain Reaction
binding of 1 neutron releases ~3 neutrons
Each neutron can initiate another reaction
Enriched 235U
Reproduction constant
K = no. of neutrons that produce a new fission event
K=1 ( self –sustained reaction)
Centrifuge separation of
isotopes
Natural Uranium is a mixture of 235U (0.7%) and 238U(99.3%)
238U is does not undergo the fission process but acts
as an absorber for neutrons. (neutron capture)
Most Uranium nuclear reactors use uranium enriched in
235U. (2-3%)
Nuclear weapons used highly enriched 235U. (~90%)
Enrichment done by mass separation.
Gaseous diffusion
Centrifuge process.
Laser separation
centrifugal
separation
gaseous UF6
3
Nuclear reactor
Nuclear reactor
fast neutrons must
be slowed down to
react efficiently.
Moderator- slows
neutrons to thermal
velocities.
Control rods- neutron
absorbers to control
the level of neutrons
Critical condition. – When each neutron released initiates
a new reaction.
Plutonium
Plutonium is a fissionable material created in
a nuclear reactor.
238
92
239Pu
−
U + 01n ⎯⎯
→ 239
94 Pu + 2e
can be made into nuclear bombs.
Pu can be chemically separated from U in spent fuel
rods from nuclear reactors.
Nuclear Fusion
High energy required to bring charged nuclei close together
+Z
v
+Z
+Z +Z
Nuclear Fusion
Fusion of small nuclei releases energy
D + 21D ⎯⎯
→ 32 He + 01n
Q= 3.27 MeV
D + 21D ⎯⎯
→ 31T + 11H
Q= 4.03 MeV
D + 31T ⎯⎯
→ 42 He + 01n
Q=17.6 MeV
2
1
2
1
2
1
Plasma Fusion
Magnetic Confinement
Plasma is a gas of ionized atoms
Heated to high temperature
Confined by magnetic forces
~10-15 M
Requirements for fusion
High Temperatures (T~ 108 K)
High density (n) for long time (τ)
T~108 K
Lawson Criterion
nτ > 1014 s/cm3
Princeton Tokomak
long times
low density
4
Laser fusionInertial Confinement
Prospects
• Nuclear energy by fission is currently a source of
much of the electrical power (~15% USA).
• The problems with nuclear energy
– Radioactive waste disposal
– Atomic bomb threats
Deuterium pellet
Short times
High density
Lawrence Livermore Lab
Nova Laser
• Nuclear fusion reactions promise an unlimited
source of energy.
– Controlled fusion reactions are not yet possible.
5