Nuclear Reactions:
AN INTRODUCTION TO
FISSION & FUSION
Farley Visitors Center
Introduction

Nuclear reactions deal with interactions
between the nuclei of atoms

The focus of this presentation are the
processes of nuclear fission and nuclear fusion

Both fission and fusion processes deal with
matter and energy
Matter and Energy

Previous studies have taught us that “matter
and energy cannot be created nor destroyed”

We now need to understand that Matter and
Energy are two forms of the same thing
E = mc2

Matter can be changed into Energy

Einstein’s formula above tells us how the change
occurs

In the equation above:
E = Energy
m = Mass
c = Speed of Light (Universal Constant)
Energy
Mass
Light
Speed
E = mc2

The equation may be read as follows:
Energy (E) is equal to Mass (m) multiplied
by the Speed of Light (c) squared

This tells us that a small amount of mass can
be converted into a very large amount of
energy because the speed of light (c) is an
extremely large number

c = 3.0 x 108 m/s
300,000,000 m/s
Fission

Fission may be defined as the process of
splitting an atomic nucleus into fission
fragments

The fission fragments are generally in the form
of smaller atomic nuclei and neutrons

Sufficient neutrons will create a chain reaction

Large amounts of energy are produced by the
fission process
Fission

Fissile nuclei are generally heavy atoms with
large numbers of nucleons

The nuclei of such heavy atoms are struck by
neutrons initiating the fission process

Fission occurs due to electrostatic repulsion
created by large numbers of protons within the
nuclei of heavy atoms
Fission

A classic example of a fission reaction is that of
U-235:
U-235 + 1 Neutron
2 Neutrons + Kr-92 + Ba-142 + Energy

In this example, a stray neutron strikes an atom of U-235.
It absorbs the neutron and becomes an unstable atom of
U-236. It then undergoes fission. Notice that more
neutrons are released in the reaction. These neutrons
can strike other U-235 atoms to initiate their fission.
Fission Reaction
Fission

The fission process is an a natural one as a
French researcher found a natural uranium
reactor in Gabon, West Africa; it has been
estimated to be over 2 billion years old

Fission produces large amounts of heat energy
and it is this heat that is captured by nuclear
power plants to produce electricity
Producing Electricity from Fission
U.S. Electrical Power Sources
Fusion

Fusion is a nuclear reaction whereby two light
atomic nuclei fuse or combine to form a single
larger, heavier nucleus

The fusion process generates tremendous
amounts of energy; refer back to Einstein’s
equation

For fusion to occur, a large amount of energy
is needed to overcome the electrical charges
of the nuclei and fuse them together
Fusion and Energy

Iron and nickel nuclei have the largest binding
energies per nucleon of all nuclei and therefore
are the most stable.

The fusion of two nuclei lighter than iron or
nickel generally releases energy.

The fusion of nuclei heavier than them
absorbs energy.
FUSION
DEUTERIUM
NEUTRON
HELIUM
TRITIUM
http://fusioned.gat.com
Fusion

Fusion reactions do not occur naturally on our
planet but are the principal type of reaction
found in stars

The large masses, densities, and high
temperatures of stars provide the initial
energies needed to fuel fusion reactions

The sun fuses hydrogen atoms to produce
helium, subatomic particles, and vast amounts
of energy
THE SUN
Cold Fusion

Efforts are being made to start and sustain
a fusion reaction at lower temperatures, in
other words with a lower amount of input
energy
Review

Mass and Energy are two forms of the same
thing; neither can be created nor destroyed but
mass can be converted into energy (E = mc2)

Fission is a nuclear reaction in which a heavy
atomic nucleus is split into lighter atomic nuclei

Fusion is a nuclear reaction in which 2 light
atomic nuclei are combined into a single,
heavier atomic nucleus
Review
Nuclear fission:
A large nucleus splits into several
small nuclei when impacted by a
neutron, and energy is released in
this process
Nuclear fusion:
Several small nuclei fuse
together and release
energy.
Quiz

Which nuclear process produces large
amounts of energy?
A. Fission
B. Fusion
C. Both fission & fusion
D. Neither fission nor fusion
Quiz

Fission is the process that _________ atomic
nuclei.
A. Combines
B. Burns up
C. Stores
D. Splits
Quiz

Mass may be converted into energy.
A. True
B. False
Quiz

The fission process requires heavy
atomic nuclei.
A. True
B. False
Quiz

Name a nuclear reaction that occurs
within the sun:
Quiz

Fission is a natural process that occurs
on the planet Earth.
A. True
B. False
Quiz

Explain this equation:
E = mc2