nuclear energy fundamentals m1 - quia

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.




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



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.



2.2 Thomson’s model (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

Electrons

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.



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).



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



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.

Table 1.1: Properties of sub-atomic particles.

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

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.

Bohr 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.

Fig. 1.7: Electron cloud model.



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 is the full chemical

symbol for 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

protons, 6 electrons and 8 neutrons

(14 – 6=8).

14

Fig. 1.8: Atomic number and

mass number.



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

Fig. 1.10: Radioactive decay.



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 Symbol Mass (kg) Charge

Alpha particle , 6.646 x 10-27 +2

Beta particle , 9.109 x 10-31 –1, (+1*)

Gamma ray none 0

Neutron

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.



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



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.



Table 1.3: Half-lives of selected isotopes.

Isotope Half-life Nuclear radiation emitted

Thorium-219 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 ,

Different substances have different half-lives as indicated Table 1.3 below.

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.



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



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..

Fig.1.15: The outline of a nuclear reactor.



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.



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 in a star is

complex, but overall hydrogen

nuclei join to form helium nuclei

Fig. 1.16: Nuclear fusion.

(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



learn how people can exploit fusion

to create a clean source of power

that uses fuels extracted from

ordinary water. Practical fusion-

based power illustrated 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.



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



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



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



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



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.



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.



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.



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

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