Transcript Unit D - Grand Junction High School

Unit D
NUCLEAR ENERGY: POWERING THE UNIVERSE (11:17 HANK)
D.1 Splitting the Atom
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During WWII, OttoHahn
and Fritz Strassman
bombarded uranium
with neutrons to create
a more massive
nucleus.
Instead, they produced
barium with only half
the atomic weight.
Scientist Lise Meitner
proposed that U atom
was split into two parts
equal in size.
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Nuclear fission
The splitting of the Uranium atom is
a nuclear fission reaction.
 Uranium-235 can fission (split) into
numerous combinations such as
barium or krypton.
 U-235 is the only naturally occurring
isotope that undergoes fission with
slow (thermal) neutrons.
 Many synthetic nuclei also fission
under bombardment.
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D.2 The Strong Force
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Fissionable isotopes such as uranium release a
million times more energy then other chemical
reactions.
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The strong force is the force that holds the nucleus
together. It is a thousand times stronger than
other types of chemical (electrical) forces that
hold compounds together.
Chemical vs. nuclear
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In a chemical reaction, the total amount of
energy involved is conserved—it does not
change—it is just transferred.
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Mass is also conserved in a chemical reaction.
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A nuclear reaction conserves both the mass and
the energy together.
Nuclear reactions: E = mc2
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Energy released (E) is
equal to the mass lost
(m) multiplied by the
speed of light squared.
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One gram of nuclear
matter can produce
energy equal to
700,000 gallons of
octane fuel.
D.3 Chain Reactions
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In nuclear fission, two or three neutrons from
each fragment are released. These in turn
can keep the reaction going by
bombarding more nuclei in a chain
reaction.
Critical Mass
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Since atoms are mostly
empty space, the
probability of a neutron
splitting another
nucleus is small unless a
minimum quantity of
material is available.
This is called the critical
mass.
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When a critical
mass of fissionable
material is present a
chain reaction
occurs.
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Such technology
led to the
production of the
atomic bomb.
How Nuclear Bombs Work
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There are two basic ways that nuclear energy
can be released from an atom.
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Nuclear fission splits the nucleus of an atom into
two smaller fragments. (U-235, U-233 or Pu-239)
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Nuclear fusion brings together two smaller atoms
(H, H-2, H-3) and forms a larger one (He, He
isotopes).
Fission Bombs
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Fission bombs use an element like U235 which can undergo induced
fission. If a free neutron runs into its
nucleus, it is absorbed, the nucleus
becomes unstable and then splits
immediately.
The two new atoms emit gamma
radiation and heat as they settle into
their new states.
The energy released is due to the fact
that the fission products and the
neutrons together weigh less than the
original U-235 atom.
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The energy released by a pound of highly
enriched uranium is equal to the amount released
from the combustion of a million gallons of
gasoline.
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A pound of uranium is the size of a baseball, while
a million gallons of gasoline would fill a 50 ft cube.
(50 ft = a five story building).
Fat Man was an
implosion-triggered
fission bomb with a
23-kiloton yield and
a 17% efficiency.
The fission usually
occurred in 560
billionths of a
second.
 Hiroshima
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Fusion Bombs-H bomb
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Fusion bombs, also
called thermonuclear
bombs have greater
efficiencies and higher
kiloton yields than
fission bombs but aren’t
as efficient because of
the chemical
properties of deuterium
and tritium.
However, fusion bombs
release more energy
than fission bombs.
Consequences of Nuclear
Explosions
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The degree of damage depends on the
distance from the center of the bomb,
also called the hypocenter or ground
zero. The closer, the more damage.
Damage is caused by:
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Intense heat from explosion.
Pressure from the shock of explosion.
Radiation
Radioactive fallout (fine radioactive particles
that fall back to the ground).
At the hypocenter, everything is vaporized in
500 million degree F /300 million degree C
temperatures.