Nuclear Energy Fundamentals
Module 1: Introduction to Nuclear
Physics
PREPARED BY
Academic Services
April 2012
© Institute of Applied Technology, 2012
ATM 1236 – Nuclear Energy Fundamentals
Module 1: Introduction to Nuclear
Physics
Module Objectives
Upon successful completion of this module, students will be able to:

Distinguish the atomic number of an element from the mass
number and use them to describe the structure of the atom and
explain isotopes.

Explain radioactive decay.

Identify the four types of nuclear radiation and their properties.

Describe how nuclear radiation occur and identify its resources.

Define the half life and distinguish the radioactive decay rates of
some elements.

Explain nuclear fission and nuclear fusion and the advantages and
disadvantages of using them as energy sources.
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Module 1: Introduction to Nuclear Physics
ATM 1236 – Nuclear Energy Fundamentals
Module 1: Introduction to Nuclear
Physics
Module Contents:
Topic
Page No.
1.
Introduction
4
2.
Understanding Atoms
4
3.
Atomic Number and Mass Number
9
4.
Isotopes
10
5.
Radioactive Decay
10
6.
Radiation Sources
12
7.
Radioactive Decay Rates
12
8.
Nuclear Fission
14
9.
The Nuclear Reactor
16
10
Nuclear Fission - Advantages and Disadvantages
18
11.
Nuclear Fusion
18
12.
Nuclear Fusion - Advantages and Disadvantages
19
13.
Check Your Understanding
20
14.
Activities
24
15.
References
27
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ATM 1236 – Nuclear Energy Fundamentals
1.
Introduction
In order to understand how nuclear power plants work we should
understand the structure of the atom first. This will give us an idea about
the nature of the nuclear fuel and will also help us recognize nuclear
reactions. These reactions produce huge amount of energy which can be
utilized to run a nuclear power plant.
2. Understanding Atoms
Since the early 19th century, scientists have known that all matter is
made up of simple particles called atoms. Scientists didn’t realize that the
atom could be “split” until the beginning of the 20th century. By changing
the structure of an atom, great amount of energy can be released.
Britain’s Joseph Thomson and New Zealand’s Ernest Rutherford made
some of the most important discoveries about atoms and nuclear physics
in the 1890s. Thomson described atoms as being like “plum pudding”
(Fig.1.2) Rutherford also studied the structure of individual atom and he
disproved this model by his scattering experiment. The early plum
pudding model is replaced by the nuclear model.
2.1
Dalton’s model
In 1803, John Dalton proposed an
atomic theory based on the law of
conservation of matter. In his view
atoms were the smallest particles of
matter (Fig. 1.1).
Fig. 1.1: Dalton’s model.
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ATM 1236 – Nuclear Energy Fundamentals
2.2
Thomson’s
model
Electrons
(Plum
pudding model) of the atom
In
this
model,
the
atom
was
imagined to be a sphere of positive
charge
with
negatively
charged
electrons dotted around inside it like
plums
in
a
pudding
(Fig.1.2).
Scientific models can be tested to
see if they are wrong by doing
experiments. Rutherford carried out
Sphere with positive charges
Fig. 1.2: Thomson’s plum pudding
model.
several experiments which showed that the atom had a very different
structure.
2.3
Rutherford’s model
The gold foil experiment was ultimately performed in order to prove
Thomson’s “plum pudding model”, although that was not the case. The
result was not as expected and in fact it proved the theory incorrect. The
experiment (Fig. 1.3) consisted mostly of alpha particles and gold foil. An
alpha particle is a helium nucleus released by radioactive substances
(discovered when Rutherford was studying radioactivity). It is a fairly
heavy, positively charged particle. To begin, polonium which is a
radioactive element was put into a lead box that sent out alpha particles
to a thin sheet of gold foil. The foil was then surrounded by a luminescent
zinc sulfide screen that served as a background for the alpha particles to
appear on. A microscope was placed above the screen so they could
easily observe any contact made between the alpha particles and the
screen. In order to see the light of the alpha rays more clearly, the
experiment
was
performed
in
complete
darkness.
To
begin
the
experiment, they aimed a beam of alpha particles at a piece of gold foil,
and then observed the astonishing results.
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ATM 1236 – Nuclear Energy Fundamentals
Fig. 1.3: Rutherford scattering experiment.
Fig. 1.4: The deflection of alpha rays.
Observation:
Most of the alpha particles passed straight through the gold foil without
any deflection from their original path A few alpha particles were
deflected through small angles and few were deflected through large
angles Very few alpha particles rebounded completely on hitting the gold
foil and turned back in (Fig. 1.4).
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Explanation:
Since most of the alpha particles pass straight through the gold foil
without any deflection it shows there is a lot of empty space in an atom
Some of the alpha particles are deflected through small and large angles,
which shows that there is a 'centre of positive charge' in an atom, which
repels the positively charged alpha particles.
Conclusions:

An atom was much more than just empty space of scattered
electrons. (as opposed to what the "plum pudding model" proposed)

An atom must have a positively charged center that contains most
of its matter. He called this dense, concentrated center the
nucleus.

The positively charged center (nucleus) was relatively small in
reference to the total size of the atom.
Fig. 1.5 shows a presentation of Rutherford model.
Fig. 1.5: Rutherford model
Fig. 1.6: Bohr’s model.
2.4 Bohr’s atomic model
In 1913 the Danish physicist Niels Bohr suggested that electrons revolve
around the nucleus just as planets revolve around the sun. Bohr’s model
agreed with Rutherford’s model of a nucleus surrounded by a large
volume of space but Bohr’s model did something that Rutherford’s model
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ATM 1236 – Nuclear Energy Fundamentals
didn’t do. It focused on electrons. As per this model each electron in an
atom has a specific amount of energy. If an atom gains or loss energy,
the energy of an electron can change. The possible energies that
electrons in an atom can have are called energy levels or shells (Fig. 1.6).
2.5 Electron Cloud Model
Rutherford didn’t stop from contemplating his work. In 1920, he explored
the possibility of the existence of a neutrally-charged particle with a
similar mass to that of a proton. This would help to keep the atom
neutral, and to fix some disparity found between the atomic number (the
number of protons) of an atom and its atomic mass (the mass of the
nucleus) which was generally higher.
In 1932, English Physicist James Chadwick confirms the existence of
neutrons, which have no charge. The protons and neutrons are found in
the nucleus at the centre of the atom. Table 1.1 shows some
characteristics of these sub-atomic particles. Note that the relative mass
is the mass of the subatomic particle divided by the mass of the neutron.
Table 1.1: Properties of sub-atomic particles.
Bohr
Particle
Charge
Mass (kg)
Relative mass
proton
+1
1.673 x 10-27
1
neutron
0
1.675 x 10-27
1
electron
–1
9.11 x 10-31
almost zero
was
correct
in
assigning
energy levels to electrons but he
was incorrect in assuming that the
electrons moved like planets in a
solar
system.
Today,
scientists
know that electrons move in a less
predictable way.
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Module 1: Introduction to Nuclear Physics
Fig. 1.7: Electron cloud model.
ATM 1236 – Nuclear Energy Fundamentals
Scientists must deal with probability when trying to predict the locations
and motions of electrons in atoms. An electron cloud is a visual model of
the most likely locations for electrons in an atom. The cloud is denser at
those locations where the probability of finding an electron is high (Fig.
1.7).
3.
Atomic Number and Mass Number
The number of protons in the nucleus of an atom is called its atomic
number:

the atoms of a particular element all have the same number of
protons.

the atoms of different elements have different numbers of protons.
Remember that most atoms are neutral because they have an equal
number of protons and electrons. Thus the atomic number also equals the
number of electrons in the atom. The total number of protons and
neutrons in an atom is called its mass number.
Atoms of the same
element could have different mass number because the number of
neutrons can vary
For example
symbol
for
is the full chemical
carbon-14.The
proton
number is shown below the chemical
symbol,
and
the
mass
number
is
shown above. In the example above,
the atomic number is 6 and the mass
number is 14 (Fig.1.8). This means
that
each
of
these
atoms
has
6
14
protons, 6 electrons and 8 neutrons
14
(14 – 6=8).
Fig. 1.8: Atomic number and
mass number.
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4.
Isotopes
An isotope is an atom that has the same number of protons but different
number of neutrons relative to other atoms of the same element. They
have the same atomic number, but different mass numbers. Fig. 1.9
shows three different isotopes of Hydrogen, namely Hydrogen (1 Electron
and 1 Proton), Deuterium (1 Electron, 1 Proton and 1 Neutron) and
Tritium (1 Electron, 1 Proton and 2 Neutrons).
Hydrogen
Deuterium
Tritium
Fig. 1.9: The three hydrogen isotopes.
5.
Radioactive Decay
The nuclei of some isotopes are
unstable. They emit particles or
release energy to become stable.
This process is called radioactive
decay. After radioactive decay, the
element changes into a different
isotope of the same element or into
entirely
different
element.
The
released energy and matter are
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Module 1: Introduction to Nuclear Physics
Fig. 1.10: Radioactive decay.
ATM 1236 – Nuclear Energy Fundamentals
collectively called nuclear radiation. Note that the term radiation can refer
to light or energy transfer. To avoid confusion, the term nuclear radiation
will be used to describe radiation associated with nuclear change.
Essentially there are four different types of nuclear radiation. It includes
alpha particles, beta particles, gamma rays or neutrons. Some of the
properties of these types are recorded in the following table. Fig 1.11
shows the penetration power and types of radiation.
Table 1.2: Types of nuclear radiation.
Radiation Type
Alpha particle
Beta particle
Gamma ray
Neutron
Symbol
Mass (kg)
Charge
,
6.646 x 10-27
+2
,
9.109 x 10-31
–1, (+1*)
none
0
1.675 x 10-27
0

* Beta particles are often fast electrons but may also be positively charged particles
called positrons which have the same mass as electrons.
The following two example gives an idea about how a nuclear radiation
occurs.
Example: Uranium-230 nuclei emit alpha radiation and become nuclei of
thorium-226:
Remember that an alpha particle is identical to a helium nucleus. Notice
that the mass number goes down by 4 and the atomic number goes down
by 2.
Fig.1.11 Types and penetration power of radiation.
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6.
Radiation Sources
The main natural radiation sources are cosmic radiation from space,
radiation from the rocks and soils around us, radon gas which comes from
the natural decay of uranium, and the radioactive materials in our bodies,
mainly from foods we eat. The sum of the exposures from these sources is
called background. In principle, we cannot prevent natural radiation from
occurring. Moreover, human activity has added to radiation by creating
and using artificial sources of radiation. These include radioactive waste
from nuclear power stations, radioactive fallout from nuclear weapons
testing and medical X-rays. Fig. 1.12 shows the contribution of different
sources to the background radiation.
Fig. 1.12: Sources of radiation and their proportion.
Artificial sources account for about 15 per cent of the average background
radiation dose. Nearly all artificial background radiation comes from
medical procedures such as receiving X-rays for X-ray photographs.
7.
Radioactive Decay Rates
If you were asked to determine the age of a rock, you would probably not
be able to do so. After all, old rocks do not look much different from new
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Module 1: Introduction to Nuclear Physics
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ones. One way to find the age of involves radioactive decay. It is
impossible to predict the moment when any particular nucleus will decay,
but it is possible to predict the time required for half of the nuclei in a
given radioactive sample to decay. The time in which half of a radioactive
substance decays is called the substance’s half life. Fig. 1.13 shows the
radioactive decay of carbon-14.
Fig. 1.13: Radioactive decay of carbon -14.
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Different substances have different half-lives as indicated Table 1.3 below.
Table 1.3: Half-lives of selected isotopes.
Isotope
Half-life
Nuclear radiation emitted
1.05 x 10-6 seconds

Radon-222
3.82 days
, 
Carbon-14
5730 years

Uranium-235
7.04 x 108 years
, 
Uranium-238
4.47 x 109 years
, 
Thorium-219
8.
Nuclear Fission
Nuclear power stations use the heat released by nuclear reactions to boil
water to make steam. The type of nuclear reaction used is called nuclear
fission.
In nuclear fission the uranium nucleus is bombarded by a neutron that
makes a large and unstable atom. Due to that the uranium nucleus splits.
Atoms of two different elements are created along with more neutrons.
These neutrons can then collide with more uranium nuclei.
These processes are repeated continuously, forming a chain reaction.
In 1938 Hahn and Strassman in their experiment observed that when
bombarding uranium-235 with neutrons as shown in Fig. 1.14, the set of
products includes two lighter nuclei, barium-141 and krypton-92, together
with neutrons and energy. This is nothing but one of the examples of
fission of uranium-235. It does not always split into Barium and Krypton
but usually into two fragments with almost equal masses.
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Fig. 1.14: Nuclear fission using uranium-235.
8.1 The strong nuclear force
The nuclear force is the force between two or more nucleons (both
proton and neutron). It is responsible for binding of protons and neutrons
into atomic nuclei. The energy released causes the masses of nuclei to be
less than the total mass of the protons and neutrons which form them.
The difference in mass is converted to energy.
8.2 Rate of energy released
Due to the nuclear force, the energy released in nuclear fission is far
greater than the energy released in a chemical reaction, such as burning
fuel. This means that the power output of a nuclear power station is large.
During fission as Fig.1.14 shows, the nucleus breaks into smaller nuclei.
The reaction also releases large amounts of energy. Each dividing nucleus
releases about 3.2 x 10-11 J of energy. In comparison, the chemical
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ATM 1236 – Nuclear Energy Fundamentals
reaction of one molecule of the explosive (TNT) releases 4.8 x 10 -18 J. In
other words one nucleus undergoing fission releases approximately the
same amount of energy as 6.7 millions TNT molecules do when they
explode.
The equivalence of mass and energy is explained by the special theory of
relativity, which Albert Einstein presented in 1905. This equivalence
means that matter can be converted into energy, and energy into matter,
and is given by the following mass-energy equation.
Energy = mass x (speed of light)2
E = mc2
The constant, c, is equal to 3 x 108 m/s. So the energy associated with
even a small mass is very large. The mass equivalent energy of 1 kg of
matter is 9 x 1016 J, which is more than the chemical energy of 22 million
tons of TNT. The huge difference in the amount of energy release is due
to the fact that in fission the mass is converted to energy.
9.
The Nuclear Reactor
The nuclear fuel is held in metal
containers called fuel rods. These are
lowered into the reactor core. A
coolant,
usually
water
or
carbon
dioxide, is circulated through the
reactor core to remove the heat.
Control rods are also lowered into the
core. These absorb neutrons and
control the rate of the chain reaction.
They are raised to speed it up, or
lowered to slow it down..
16
Fig.1.15: The outline of a nuclear
reactor.
Module 1: Introduction to Nuclear Physics
ATM 1236 – Nuclear Energy Fundamentals
Uranium or plutonium isotopes are normally used as the fuel in nuclear
reactors, because their atoms have relatively large nuclei that are easy to
split, especially when hit by neutrons. Fig. 1.15 shows an outline of a
nuclear reactor.
Fig.1.11: The outline of a nuclear reactor.
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ATM 1236 – Nuclear Energy Fundamentals
10.
Nuclear Fission - Advantages and Disadvantages
In considering the subject of nuclear power, it is important to weigh up
the
advantages
and
the
disadvantages.
These
are
some
of
the
advantages:
no carbon dioxide is produced when the station is operating, as

stated earlier.

there is a high power output.

a small amount of fuel is needed, when compared with coal or gas.
These are some of the disadvantages:

hazardous radioactive waste is produced.

building the power stations is quite expensive.

Taking apart the power stations at the end of their lifetime is very
costly.
11.
Nuclear Fusion
Nuclear fusion involves two atomic
nuclei
joining
to
make
a
large
nucleus. Energy is released when
this happens. The Sun and other
stars use nuclear fusion to release
energy. The sequence of nuclear
fusion
reactions
complex,
but
in
overall
a
star
is
hydrogen
Fig. 1.16: Nuclear fusion.
nuclei join to form helium nuclei
(Fig. 1.16). Some scientists estimate that 1 kg of hydrogen in a fusion
reactor could release as much energy as 16 million kg of burning coal. The
fusion reaction itself releases very little waste or pollution. Scientists are
conducting many experiments in the United States, Japan and Europe to
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Module 1: Introduction to Nuclear Physics
ATM 1236 – Nuclear Energy Fundamentals
learn how people can exploit fusion
to create a clean source of power
that
uses
ordinary
based
fuels
water.
power
extracted
Practical
illustrated
from
fusion-
by
the
concept drawing in Fig. 1.17 is far
from being a reality.
Fig. 1.17: ITER experimental
nuclear fusion research reactor.
12.
Nuclear Fusion – Advantages and Disadvantages
There are advantages and disadvantages of nuclear fusion; the main
advantage is that the fuel used for fusion (hydrogen) is very abundant.
Earth’s oceans could provide enough hydrogen to meet current world
energy demands for millions of years.
Fusion reactions have some drawbacks. They can produce fast neutrons, a
highly energetic and dangerous form of nuclear reaction. This requires
replacing the shielding material periodically which makes the operation of
the fusion power plant expensive and impractical. Lithium can be used to
slowdown these neutrons, but lithium is chemically reactive and rare so its
use is not practical.
Research on nuclear fusion is still developing and successful experiments
are just beginning. The world is still waiting for the perfect fuel to come.
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ATM 1236 – Nuclear Energy Fundamentals
13.
Check Your Understanding
1. What sort of reaction has happened when hydrogen atoms become a
helium atom?
a.
Chemical reaction.
b.
Ionic reaction.
c.
Nuclear reaction.
d.
None of the above.
2. What does not happen when a nucleus splits?
a.
Nuclear fusion
b.
Radiation is released
c.
New nuclei are formed
d.
New elements are formed
3. Two fissionable substance commonly used in nuclear reactors include:
a.
helium-3 and Deuterium
b.
uranium-235 and Tritium
c.
uranium-239 and plutonium-235
d.
uranium-231 and plutonium-245
4. The chain reaction in nuclear reactors needs the absorption of:
a.
neutrons
b.
electrons
c.
protons
d.
helium
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Module 1: Introduction to Nuclear Physics
ATM 1236 – Nuclear Energy Fundamentals
5. Which of these is not a natural source of radiation?
a.
Food and drink
b.
Medical X-rays
c.
Cosmic rays
d.
Rocks
6. Which contributes most to our average dose of background radiation?
a.
Natural sources
b.
Nuclear weapons
c.
Natural and artificial sources both contribute 50 per cent
d.
Artificial sources
7. Given the diagram representing a reaction. Which phrase best describes
this type of reaction and the overall energy change that occurs?
a.
Nuclear, and energy is released
b.
Chemical, and energy is released
c.
Chemical, and energy is absorbed
d.
Nuclear, and energy is absorbed
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ATM 1236 – Nuclear Energy Fundamentals
8. Which balanced equation represents nuclear fusion?
a.
b.
c.
d.
9 The energy released by a nuclear reaction results primarily from the
_______.
a.
conversion of energy into mass
b.
conversion of mass into energy
c.
formation of bonds between atoms
d.
breaking of bonds between atoms
10. A nuclear fission reaction and a nuclear fusion reaction are similar
because both reactions _______.
a.
absorb a large amount of energy
b.
form heavy nuclides from light nuclides
c.
form light nuclides from heavy nuclides
d.
release a large amount of energy
11. The amount of energy released from a fission reaction is much greater
than the energy released from a chemical reaction because in a
fission reaction ________.
a.
covalent bonds are broken
b.
ionic bonds are broken
c.
energy is converted into mass
d.
mass is converted into energy
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ATM 1236 – Nuclear Energy Fundamentals
12. Nuclear fusion differs from nuclear fission because nuclear fusion
reactions ________.
a.
form heavier isotopes from lighter isotopes
b.
convert energy to mass
c.
convert mass to energy
d.
form lighter isotopes from heavier isotopes
13. In a nuclear fusion reaction, the mass of the products is _______.
a.
more than the mass of the reactants because some of the energy
has been converted to mass
b.
more than the mass of the reactants because some of the mass
has been converted to energy
c.
less than the mass of the reactants because some of the energy
has been converted to mass
d.
less than the mass of the reactants because some of the mass
has been converted to energy
14. An alpha particle is identical to a(n) _______.
a.
neutron
b.
electron
c.
Helium nucleus
d.
Hydrogen nucleus
15. The half-life of cobalt-60 is 5.3 years. What fraction of a sample
remains after 15.9 years?
a.
One half.
b.
One quarter.
c.
One sixth.
d.
One eighth
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ATM 1236 – Nuclear Energy Fundamentals
14. Activities
14.1 Electron cloud model
Purpose:
You will use a model to describe the probable position of electrons.
Material:
Small, round balloon; large, round balloon; 10 beads with 4 mm diameter;
5 beads with 2 mm diameter.
Procedure:
1. Put the 4 mm beads into the small balloon. This represents the
nucleus of Boron atom (5 proton and 5 neutrons)
2. Put the 2 mm beads into the large balloon. The beads represent the
electrons and the balloon represents the electron cloud.
3. Slightly inflate the small balloon and push it completely into the
large balloon.
4. Inflate the large balloon and tie the end.
5. Shake the balloon so that the small beads are in constant motion.
6. Note that the precise location of the beads (electrons) at a specific
time is unknown. But the probability that it is in the large balloon is
quite high.
14.2 Modeling radioactive decay
Purpose:
You will use a model to describe the radioactive decay.
Material:
50 coins to represent 50 atoms of a radioactive isotopes. In this
simulation, heads indicates that the nucleus has not decayed.
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ATM 1236 – Nuclear Energy Fundamentals
Procedure:
1. Record 50 heads as the starting point.
2. Shake all the coins in a large cup and pour them out. Remove all the
tails and set them aside. Count and record the number of heads.
3. Repeat step 2 with the coins that wee heads in the last throw. Each
throw simulate one half-life.
4. Graph the number of coins as a function of the number of half-lives.
5. Collect the results from other students and use the totals to make
new graph.
6. Compare this graph with the one in Fig. 1.12.
14.3 Chain reaction
Purpose:
You will use a model to describe the chain reaction.
Material:
Ruler and 15 dominos.
Procedure:
1. Arrange the dominos as shown in Fig. 1.18.
Fig. 1.18: Dominos pattern
2. Now knock over the first domino and watch what happens.
3. Repeat the steps 1 and 2 but use a ruler in one of the branches and
see what happen. The ruler works as control rods used to control
the chain reaction in nuclear reactors.
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ATM 1236 – Nuclear Energy Fundamentals
14.4 Research
Two atomic bombs were dropped on Hiroshima and Nagasaki during the
Second World War. The code names for these are the "Little Boy" and the
"Fat Man". Right a brief report to explain the development of the bombs
the basic design, the nuclear fuel used, the physical effects of the bomb,
etc.
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ATM 1236 – Nuclear Energy Fundamentals
15.

References
Physical Science with Earth and Space Science. Holt, Rinehart and
Winston.

Physical
Science,
Concepts
in
Action,
Wysession,
Frank,
Yancopoulos. Person Education Inc.

Physics Principles and Problems
Zitzewitz et al. Mc Graw-Hill
Glenco.

Chemistry Concepts and Applications Mc Graw-Hill Glenco.

Why Science Matters, Using Nuclear Energy by John Townsend,
Heinemann.

http://www.furryelephant.com

http://www.tvakids.com/teachers/sourcebooks.htm

http://www.energyquest.ca.gov/projects

http://www.nrc.gov/materials/

http://www.nfi.co.jp/e/product/prod02.html

http://www.euronuclear.org/info/encyclopedia/g/gascentrifuge.htm

http://en.wikipedia.org/wiki/Nuclear_fission

http://library.thinkquest.org/17940/texts/fission/fission.html

http://www.atomicarchive.com/Fission/Fission4.shtml

http://phet.colorado.edu/en/simulation/nuclear-fission

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/radiati
on/nuclearfissionrev1.shtml
Module 1: Introduction to Nuclear Physics
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