Ch19 Nuclear Reactions
Harnessing the Power of the Sun
Nuclear vs. Chemical
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Chemical changes involve the transfer of
electrons. In chemical reactions atoms
are re-arranged to form new products.
Nuclear reactions involve a change in the
nucleus of the atom.
A change in protons or neutrons will
create a new species, either an isotope or
a new element.
Notation
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Mass number is the total number of
protons and neutrons.
Atomic number is the total number of
protons
Nuclear changes are balanced using
conservation of mass number and atomic
number
“Use the force Luke”
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What holds the net
positive nucleus
together?
The strong nuclear
force overcomes the
electrostatic repulsion
of the protons and
binds the nucleus
together.
Nuclear Binding Energy
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Energy is required to bind the nucleus
together.
This energy comes from the difference in
mass between the atom and its parts.
Mass defect is the difference in mass
between the number of neutrons and
protons and the mass of the nucleus
together.
E = mc2 gives the amount of energy
Mass Defect
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Proton Mass = 1.007825
Neutron mass = 1.008665
Mass of O-16 is 15.994915
Difference in mass between 8 protons and
8 neutrons is the mass defect (.137005).
It is converted into energy to hold the
nucleus together using e=mc2.
Nuclear Decay
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Nuclear processes occur because of an
instability between the number of protons
and neutrons in the nucleus.
During nuclear reactions, a particle from
the nucleus is given off which results in:
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Change of proton to a neutron
Change of neutron to a proton
Release of energy and radiation
Valley of
Stability
indicates stable
nuclei. The
ratio of neutrons
to protons
increases for
stable nuclei as
mass number
increases.
Nuclear Decay Particles

Alpha particle
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A particle with 2 protons and 2 neutrons
Alpha particles are emitted
The net effect is to lose 4 nuclei particles from
the nucleus
The daughter particle is the element two
elements back on the periodic table.
Nuclear Decay Particles

Beta particle ß
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Electron emitted from the nucleus
Changes a neutron to a proton
The daughter formed is the next element on
the periodic table
Nuclear Decay Particles

Positron emission ß+
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Positive electron emitted from the nucleus
Changes a proton to a neutron
The daughter formed is the element directly
behind the parent nuclei.
Nuclear Decay Particles

Gamma particle
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A high energy particle of radiation, no mass
The particle is given off as the nucleus returns
to a lower energy state
The parent and daughter are the same
Nuclear Decay Particles

Electron Capture
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Turns a proton to a neutron by capturing an
electron
The same process as positron emission
The daughter formed is the element
preceding the parent nucleus.
Radioactive equations
Atomic Fission
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Nuclear fission occurs when a heavy
nucleus such as U-235 splits into two
smaller nuclei.
The total rest mass of the products is less
than the original rest mass.
The mass difference is converted to the
energy released using e=mc2
This process occurs naturally at a slow
rate, but can be accelerated by neutron
bombardment in the laboratory.
Neutron Bombardment of U-235
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U  n U
235
92
1
0
236
92
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U  X  Y  neutrons
236
92
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U  Ba  Kr 3 n
236
92
141
56
92
36
1
0
U-235 absorbs a
slow moving
neutron.
U-236 is unstable
and lasts for only
10-12 s.
The U-236 nucleus
splits into two
fragments and
emits several
neutrons.
Nuclear Fusion
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Lighter nuclei undergo a process called
nuclear fusion
Fusion takes a great amount of energy to
be initiated in order to overcome the
proton-proton barrier between nuclei.
However, a greater amount of energy is
released in the process.
Stars produce their energy through the
fusion process.
Fusion Process
1
1
H  H  H  e 
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H  H  He  
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1
1
1
1
1
1
2
1
2
1
0
1
3
2
H  He He  e 
3
2
4
2
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0
1

3
2
He  He He  H  H
3
2
4
2
1
1
1
1
Hydrogen is fused
together forming
deuterium.
He-3 is formed
from hydrogen
isotopes.
He-4 is formed
through 2 different
processes.
The energy is
produced though
the gamma,
neutrino, and
positron emission.