Name___________________________________Date_____________________ Period_____
STANDARD 11 NUCLEAR PROCESSES
This standard requires a knowledge of chemical and physical concepts and sufficient mathematical skills to
describe the nucleus and its subatomic particles. Topics covered are nuclear reactions and their accompanying
changes in energy and forms of radiation and quantification of radioactive decay as a function of time. Recall
that the mass and charge of the proton is 1 amu and positive, respectively; and the mass and charge of the
neutron are 1 amu and no charge. Remember that an element’s average atomic mass is based on the abundance
and the mass number for individual isotopes. The nucleus of atoms are held together strong nuclear force which
overcomes the repulsion between charged protons at very close distances.
Nuclear processes are those in which an atomic nucleus changes, including radioactive decay of
naturally occurring and human-made isotopes, nuclear fission, and nuclear fusion. As a basis for
understanding this concept:
11 a. Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome
the electromagnetic repulsion between the protons.
The nucleus is held together by the strong nuclear force. The strong nuclear force acts between protons,
between neutrons, and between protons and neutrons but has a limited range comparable to the size of an
atomic nucleus. The nuclear force is able to overcome the mutual electrostatic repulsion of the protons only
when the protons and neutrons are near each other as they are in the nucleus of an atom.
Atomic Structure Atoms are made up of three tiny particles called protons, neutrons and electrons.
Particle
Proton
Neutron
Electron
Position in atom
Nucleus
Nucleus
In energy levels (shells)
outside the nucleus
Charge
Positive
No charge
Negative
Mass
1
1
Negligible
Atoms have no overall electrical charge because the number of positive protons and negative electrons are
equal, so they cancel each other out.
The number of protons in the nucleus of an atom determines what element it is. Atoms of
the same element have the same number of protons.
At the centre of an atom is the nucleus, which is very small. It has a positive charge because
it contains protons. It is very dense because it contains protons and neutrons which make up
most of the mass of an atom. The total number of protons and neutrons (nucleons) in an
atom is called its mass number, or nucleon number.
11 b. Students know the energy release per gram of material is much larger in nuclear fusion or fission
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reactions than in chemical reactions. The change in mass (calculated by E = mc ) is small but significant in
nuclear reactions.
Two major types of nuclear reactions are fusion and fission. In fusion reactions two nuclei come together and
merge to form a heavier nucleus. In fission a heavy nucleus splits apart to form two (or more) lighter nuclei. The
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binding energy of a nucleus depends on the number of neutrons and protons it contains. A general term for a
proton or a neutron is a nucleon. In both fusion and fission reactions, the total number of nucleons does not
change, but large amounts of energy are released as nucleons combine into different arrangements. This
energy is one million times more than energies involved in chemical reactions.
Nuclear energy is the energy that is trapped inside each atom. One of the laws of the
universe is that matter and energy can't be created nor destroyed. But they can be
changed in form. Matter can be changed into energy. The world's most famous scientist,
Albert Einstein, created the mathematical formula that explains this. It is:
E = m c
2
This equation says:
E [energy] equals m [mass] times c2 [c stands for the velocity or the speed of light. c2
means c times c, or the speed of light raised to the second power -- or c-squared.]
You can listen to Einstein's voice explaining this at: www.aip.org/history/einstein/voice1.htm
Scientists used Einstein's famous equation as the key to unlock atomic energy and also create atomic bombs.
Nuclear Fission1
An atom's nucleus can be split apart. When this is done, a
tremendous amount of energy is released. The energy is both heat
and light energy. Einstein said that a very small amount of matter
contains a very LARGE amount of energy. This energy, when let out
slowly, can be harnessed to generate electricity. When it is let out
all at once, it can make a tremendous explosion in an atomic bomb.
A nuclear power plant (like Diablo Canyon Nuclear Plant shown
below) uses uranium as a "fuel." Diablo Canyon is located in San
Luis Obispo County and is scheduled for permit renewal in 2024.
Uranium is an element that is dug out of the ground many places
around the world. It is processed into tiny pellets that are loaded into very long rods that are put into the
power plant's reactor. The word fission means to split apart. Inside the reactor of an atomic power plant,
uranium atoms are split apart in a controlled chain reaction.
Inside a nuclear reactor, unstable atoms with large nuclei are bombarded with neutrons. This causes the nuclei
of the atoms to split into two smaller nuclei. This is called nuclear fission. Further neutrons are released
which can hit other atoms causing further nuclear fission. This is called a chain reaction.
The new atoms formed are also radioactive. Many of these have very long half-lives, so will be
dangerous for many years. This material could hurt people if released, so it is kept in a solid
form. The very strong concrete dome in the picture is designed to keep this material inside if an
accident happens. Large amounts of energy are released during radioactive decay or nuclear
fission. This energy can be transferred into electrical energy in a nuclear power station, or used
destructively as with a nuclear bomb.
In a chain reaction, particles released by the splitting of the atom go off and strike other
uranium atoms splitting those. Those particles given off split still other atoms in a chain
reaction. In nuclear power plants, control rods are used to keep the splitting regulated so it
doesn't go too fast.
1
http://www.energyquest.ca.gov/story/chapter13.html
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If the reaction is not controlled, you could have an atomic bomb. But in atomic bombs, almost pure pieces of
the element Uranium-235 or Plutonium, of a precise mass and shape, must be brought together and held
together, with great force. These conditions are not present in a nuclear reactor.
This chain reaction gives off heat energy. This heat energy is used to boil water in the core of the reactor. So,
instead of burning a fuel, nuclear power plants use the chain reaction of atoms splitting to change the energy
of atoms into heat energy. A lot of water is required for nuclear plants.
This water from around the nuclear core is sent to
another section of the power plant. Here, in the heat
exchanger, it heats another set of pipes filled with
water to make steam. The steam in this second set of
pipes turns a turbine to generate electricity. Below is a
cross section of the inside of a typical nuclear power
plant.
Power plant drawing courtesy Nuclear Institute
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Nuclear Fusion
Another form of nuclear energy is called fusion. Fusion
means joining smaller nuclei (the plural of nucleus) to make
a larger nucleus. The sun uses nuclear fusion of hydrogen
atoms into helium atoms. This gives off heat and light and
other radiation.
In the picture to the right, two types of hydrogen atoms,
deuterium and tritium, combine to make a helium atom and
an extra particle called a neutron.
Also given off in this fusion reaction is energy! The same
energy that fuels the sun and stars.2 Scientists have been working on controlling nuclear fusion for a long time,
trying to make a fusion reactor to produce electricity. But they have been having trouble learning how to
control the reaction in a contained space.
What's better about nuclear fusion is that it creates less radioactive material than fission, and its supply of
fuel can last longer than the sun.
11. c. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in
nuclear reactions.
Sometimes atoms with the same number of protons in the nucleus have different numbers of neutrons. These
atoms are called isotopes of an element. Both naturally occurring and human-made isotopes of elements can be
either stable or unstable. Less stable isotopes of one element, called parent isotopes, will undergo radioactive
decay, transforming to more stable isotopes of another element, called daughter products, which can also be
either stable or radioactive. For a radioactive isotope to be found in nature, it must either have a long half-life,
such as potassium-40, uranium-238, uranium-235, or thorium-232, or be the daughter product, such as radon222, of a parent with a long half-life, such as uranium-238.
Isotopes Atoms of the same element which have different numbers of neutrons are called isotopes. Carbon
exists in three forms:
number of protons
number of electrons
number of neutrons
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C
6
13
C
6
14
C
6
6
6
6
6
6
7
6
6
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Some isotopes are radioactive. These are radioisotopes or radionuclides. Their nuclei are unstable and can
spontaneously split up, emitting radiation and producing a new atom, with a different number of protons. This is
called radioactive decay and is a random process – you don’t know which atoms may suddenly undergo a nuclear
change. Radioisotopes called tracers are used determine complex metabolic pathways – How photosynthetic
reactions discovered.
2
http://www.atomicarchive.com/Fusion/Fusion1.shtml
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Examples of isotopes
Element
Carbon
Potassium
Stable isotopes
Carbon-12
Carbon-13
Potassium-39
Potassium-41
Uranium
Unstable isotopes
Carbon-14
Where found
Air, plants and animals
Potassium-40
Rocks, plants and sea water
Uranium-234
Uranium-235
Uranium-238
Rocks
Simple hydrogen, deuterium, and tritium nuclei illustrate and define isotopes. Recall that isotopes
have the same number of protons but different numbers of neutrons and thereby atomic mass.
11. d. Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know
how the nucleus changes in each type of decay. Radioactive isotopes transform to more stable isotopes,
emitting particles from the nucleus. These particles are helium-4 nuclei (alpha radiation), electrons or positrons
(beta radiation), or high-energy electromagnetic rays (gamma radiation).
In 1896, Henri Becquerel discovered radioactivity. Radioactivity is the spontaneous emission of energy and
particles by atoms of certain elements producing new elements. Materials that emit this kind of radiation are
said to be radioactive and to undergo radioactive decay. In 1899, Ernest Rutherford discovered that uranium
compounds produce three different kinds of radiation. He separated the radiations according to their
penetrating abilities and named them:
alpha, β beta, and γ gamma radiation, after the first three letters of the Greek alphabet.
Alpha decay
In alpha decay, the nucleus emits an alpha particle; an alpha particle is essentially a helium nucleus, so it is a
group of two protons and two neutrons. A helium nucleus is very stable. Alpha radiation can be stopped by a
sheet of paper.
An example of an alpha decay involves uranium-238:
Ionization smoke detectors use an ionization chamber and a source of ionizing radiation to detect smoke. This
type of smoke detector is more common because it is inexpensive and better at detecting the smaller amounts
of smoke produced by flaming fires. Inside an ionization detector is a small amount (perhaps 1/5000th of a
gram) of americium-241. The radioactive element americium has a half-life of 432 years, and is a good source of
alpha particles.
Beta decay
A beta particle is an electron. In beta decay an electron is involved. The number of neutrons in the nucleus
decreases by one and the number of protons increases by one. Six millimeters of aluminum are needed to stop
most beta particles
An example of such a process is:
Gamma decay
The third class of radioactive decay is gamma decay, in which the nucleus changes from a higher- level energy
state to a lower level. Several millimeters of lead are needed to stop gamma rays.
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
Isotopes of elements that undergo alpha decay produce other isotopes with two less protons and two
less neutrons than the original isotope. Uranium-238, for instance, emits an alpha particle and becomes
thorium-234.

Isotopes of elements that undergo beta decay produce elements with the same number of nucleons but
with one more proton or one less proton. For example, thorium-234 beta decays to protactinium-234,
which then beta decays to uranium

Alpha and beta decay are ionizing radiations with the potential to damage surrounding materials. After
alpha and beta decay, the resulting nuclei often emit high-energy photons called gamma rays. This
process does not change the number of nucleons in the nucleus of the isotope but brings about a lower
energy state in the nucleus.
11.e.
Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in
matter and have different penetrations. Alpha, beta, and gamma rays are ionizing radiations, meaning that
those rays produce tracks of ions of atoms and molecules when they interact with materials. For all three types
of rays, the energies of particles emitted in radioactive decay are typically for each particle on the order of
1MeV, equal to 1.6 × 10
−13
joule, which is enough energy to ionize as many as half a million atoms.
Types of Nuclear Radiation
Alpha particles are helium nuclei, so they have two protons and two neutrons, but no electrons.
They carry a 2+ charge. The nuclear emission that has the greatest mass and least penetration ability.
Alpha particles have the shortest ranges, and matter that is only a few millimeters thick will stop them. They
will not penetrate a thick sheet of paper but will deposit all their energy along a relatively short path, resulting
in a high degree of ionization along that path.
Beta particles are high energy electrons emitted from the nucleus of an atom. They carry a negative
charge.
Beta particles have longer ranges, typically penetrating matter up to several centimeters thick. Those
particles are electrons or positrons (the antimatter electron), have one unit of either negative or positive
electric charge, and are approximately 1/2000 of the mass of a proton. These high-energy electrons have longer
ranges than alpha particles and deposit their energy along longer paths, spreading the ionization over a greater
distance in the material.
Gamma rays are very short wavelength electromagnetic waves which travel at the speed of light.
They do not have a charge. Because there is no charge this type of radiation will pass directly through
an electric field without being detected.
Gamma rays can penetrate matter up to several meters thick. Gamma rays are high-energy photons that have
no electric charge and no rest mass (the structural energy of the particle). They will travel unimpeded through
materials until they strike an electron or the nucleus of an atom. The gamma ray’s energy will then be either
completely or partially absorbed, and neighboring atoms will be ionized.
Therefore, these three types of radiation interact with matter by losing energy and ionizing surrounding atoms.
Alpha radiation is dangerous if ingested or inhaled. For example, radon-222, a noble gas element, is a naturally
occurring hazard in some regions. Living organisms or sensitive materials can be protected from ionizing
radiation by shielding them and increasing their distance from radiation sources. Most common exposure.
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The order of penetrating ability, from greatest to least, is gamma > beta > alpha, and this order is the basis for
assessing proper shielding of radiation sources for safety.
There are a number of naturally occurring sources of ionizing radiation. One is potassium-40, which can be
detected easily in potash fertilizer by using a Geiger counter. The other is background cosmic and alpha
radiation from radon.
Workers who may be exposed to radiation have to wear a radiation badge, which monitors the amount of
radiation the person has been exposed to over a period of time. The badge contains a piece of photographic film.
The film darkens if exposed to radiation. The more radiation a worker has been exposed to, the darker the film
goes.
11. f.* Students know how to calculate the amount of a radioactive substance remaining after an integral
number of half-lives have passed.
Radioactive decay transforms the initial (parent) nuclei into more stable (daughter) nuclei with a characteristic
half-life. The half-life is the time it takes for one-half of a given number of parent atoms to decay to daughter
atoms. One-half of the remaining parent atoms will then decay to produce more daughter atoms in the next
half-life period. It is possible to predict only the proportion, not the individual number, of parent atoms that
will undergo decay. Therefore, after one half-life, 50 percent of the initial parent nuclei remain; after two halflives, 25 percent; and so forth. The intensity of radiation from a radioactive source is related to the half-life
and to the original number of radioactive atoms present.
Radioactive Dating
Radioactive materials gradually decay and form new atoms. The time it takes for half the atoms in a
sample to decay is called its half-life, so older samples emit less radiation. This idea is used to work
out how old plant, animal and rock specimens are.

Carbon-14 is used to date things that were once living.

Uranium isotopes have very long half-lives and decay via a series of short-lived radioisotopes
to produce stable isotopes of lead. The relative amounts of uranium and lead in a sample of
igneous rack can be used to date the rock.

Potassium-40 decays to form argon. The proportions of radioactive potassium and stable
argon can be used to date igneous rocks from which the gaseous argon has been unable to
escape.
The more unstable the nuclei the shorter the half-life. Substances with long half-lives are often the
most dangerous because they stay radioactive for many years.
For example, the half life of uranium-238 is
4500 million years. If a rock sample contains
three times as many lead atoms as uranium
atoms, and we assume there was no lead in the
rock when it was formed, we can calculate its
age.
After 4500 million years half the atoms would
be uranium-238 and half would be lead. After
another 4500 million years half of these uranium
atoms would have decayed to lead, producing a
rock containing three times as much lead as
uranium. The age of the rock would therefore be 9000 million years.
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1. Given that the half-life of carbon-14 is 5730 years, how old is a fossilized organism that
contains 25.0% of the carbon-14 it did when it was alive?
a. 11 460 y
b. 5730 y
c. 22 920 y
d. 17 190 y
2. These particles sustain a nuclear fission chain reaction
a. Protons
c. beta particles
b. alpha particles
d. neutron
3. In Einstein's famous equation E = mc2, which relates energy and mass, c represents
the ___________________.
a. caloric content
c. specific heat
b. speed of sound
d. speed of light
4. Exposure to ________________ can extend the shelf life of food
a. Heat
c. bacteria
b. gamma radiation
d. alpha particles
5. This radioactive isotope is commonly used to determine the age of once-living
organisms.
a. carbon-14
c. nitrogen-14
b. sodium-23
d. oxygen-16
6. If a thorium-230 atom undergoes alpha decay, what are the products of the reaction?
a. radium and an alpha particle
c. actinium and an alpha particle
b. actinium and a positron
d. radium and a positron
7. Which of the following types of radiation will pass directly through an electric field
without being deflected?
a. beta particle
c. alpha particle
b. gamma ray
d. delta ray
8. The half-life of technetium-99 is 6.0 hours. How much of a 1.000-gram sample remains
after 18.0 hours?
a. 0.500 g
b. 0.125 g
c. 8.000 g
d. 0.250 g
9. _____________ produces a form of high-energy electromagnetic radiation.
a. Gamma decay
c. Beta decay
b. Delta decay
d. Alpha decay
10. The products of the fusion reaction involving deuterium and tritium are a neutron and
this particle.
a. a beta particle
c. a protium nucleus
b. a U-235 nucleus
d. an alpha particle
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11. In an ionizing smoke detector, smoke particles interfere with the flow of ions created by
_____________ from americium-241.
a. Atoms
c. gamma rays
b. alpha particles
d. electrons
12. ____________ containing radioactive P-32 have been used to help clarify complex
metabolic pathways.
a. Protons
c. U-235 atoms
b. Fusion reactors
d. Tracer
13. Unstable atomic nuclei emit radiation to __________.
a. lose protons
b. attain more stable atomic configurations
c. gain electrons
d. gain neutrons
14. If one fission reaction of a uranium-235 atom produced two neutrons, how many
neutrons would be released if the chain reaction occurred three more times?
a. 2
c. 8
b. 4
d. 16
15. The half-life for tritium is 12.32 years. How long will it take for a 10.00-g sample of
tritium to decay until 1.875 g remain?
a. 0.6594 years
b. 5.333 years
c. 24.64 years
d. 30.80 years
16. Radioactivity is the spontaneous emission of radiation by a/an _____________.
a. hydrogen bond
c. covalent bond
b. stable electron
d. unstable atomic nucleus
17. These devices produce most artificial elements.
a. fission reactors
b. fusion reactors
c. particle accelerators
d. centrifuges
18. Two or more atomic nuclei combine to form a larger nucleus in this process.
a. nuclear fission
c. nuclear fusion
b. nuclear splitting
d. covalent bonding
19. _________ absorb some neutrons in a fission reactor to maintain the rate of reaction.
a. Cooling towers
c. turbines
b. Graphite blocks
d. Control rods
20. The splitting of an atomic nucleus into two or more large fragments is called ________.
a. alpha decay
c. nuclear fission
b. nuclear fusion
d. beta decay
21. This element accounts for most of the radiation to which people are exposed.
a. Radon
c. Carbon
b. Hydrogen
d. phosphorus
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What do we know about the radiation from radioactive substances?
Background Radiation | Types of Radiation | Dangers of Radiation | Half-life | Uses of Radiation
Background Radiation
Some substances give out radiation all the time. They are said to be radioactive. Radioactive
atoms are unstable and will randomly break down.
When this happens the nucleus of some atoms breaks up and gives out radiation.
There are radioactive substances all around us – in the ground, in air, in building materials and
in food. Radiation also reaches us from space. The radiation from all these sources is called
background radiation.
Types of Radiation
There are three types of radiation that are emitted by radioactive substances:
Alpha particles – not very penetrating. They are absorbed by a few centimetres of air or thin
paper.
Beta particles – moderately penetrating. They pass through air or paper easily, but are
absorbed by a few millimetres of metres.
Gamma rays – very penetrating electromagnetic waves. They are absorbed by several
centimetres of lead, or several metres of concrete.
As radiation passes through a material it can be absorbed. The thicker the material, the more
radiation is absorbed.
Dangers of Radiation
When radiation from radioactive substances collides with neutral atoms or molecules these may
become ionized. This means they form charged particles called ions. If molecules inside living
cells become ionized they can cause damage, including cancer. The bigger the dose of radiation,
the greater the chance of cancer. Higher doses of radiation can kill cells.
When sources of radiation are outside the body alpha radiation is the least dangerous
because it cannot penetrate the skin, so is unlikely to reach living cells. Beta and gamma
radiation are the most dangerous because they can penetrate the skin and reach cells of organs,
which may absorb them. Workers who may be exposed to radiation have to wear a radiation
badge, which monitors the amount of radiation the person has been exposed to over a period of
time. The badge contains a piece of photographic film. The film darkens if exposed to radiation.
The more radiation a worker has been exposed to, the darker the film goes.
If radioactive sources are inside the body alpha radiation is the most dangerous because it
is strongly absorbed by the cells.
Beta and gamma radiation are less dangerous because fewer cells will absorb the radiation
because they can penetrate the tissues.
Uses of Radiation


To kill cancer cells.
To kill harmful microorganisms
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
To monitor and control the thickness of manufactured materials, for example, paper,
rubber and metal sheets.
A beta source is usually used.
If the sheet stays the correct thickness the detector
picks up and displays a steady reading.
If the reading goes up, the sheet is too thin, if it falls the
sheet is too thick.

As radioactive tracers in hospitals to build up a
picture of what is happening inside the body.
The radioactive sources used are usually gamma emitters, so the radiation passes through the
body to a detector and little is absorbed by the cells. They have fairly short half-lives so that
they decay quickly to minimize any cell damage.
Adapted from: http://lgfl.skoool.co.uk/examcentre.aspx?id=690
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This model of the atom was developed by Rutherford and Marsden. They directed a beam of alpha
particles at a very thin piece of metal. Most particles went straight through the metal atoms,
suggesting that most of the atom must be empty space.
A few particles were scattered at different angles.
Alpha particles carry a positive charge, so Rutherford concluded that they must be repelled by a small
area of great positive charge. He called this the nucleus.
This model replaced an earlier ‘plum pudding’ model. The earlier model described an atom as
having negative charges embedded in a positive dough. Rutherford and Marsden’s scattering
experiment disproved this theory.
'Plum pudding' model of an atom
The Hydrogen Bomb: The Secret
The question facing designers was "How do you build a bomb that will maintain the high temperatures required
for thermonuclear reactions to occur?" The shock waves produced by the primary (A-bomb) would propagate too
slowly to permit assembly of the thermonuclear stage (the secondary) before the bomb blew itself apart. This
problem was solved by Edward Teller and Stanislaw Ulam.
To do this, they introduced a high energy gamma ray absorbing material (styrofoam) to capture the energy of the
radiation. As high energy gamma radiation from the primary is absorbed, radial compression forces are exerted
along the entire cylinder at almost the same instant. This produces the compression of the lithium deuteride.
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Additional neutrons are also produced by various components and reflected towards the lithium deuteride. With
the compressed lithium deuteride core now bombarded with neutrons, tritium is formed and the fusion process
begins.
The Hydrogen Bomb: Schematic
The yield of a hydrogen bomb is controlled by the amounts of lithium deuteride and of additional fissionable
materials. Uranium 238 is usually the material used in various parts of the bomb's design to supply additional
neutrons for the fusion process. This additional fissionable material also produces a very high level of radioactive
fallout.
The Neutron Bomb
The neutron bomb is a small hydrogen bomb. The neutron bomb differs from standard nuclear weapons insofar as
its primary lethal effects come from the radiation damage caused by the neutrons it emits. It is also known as an
enhanced-radiation weapon (ERW).
The augmented radiation effects mean that blast and heat effects are reduced so that physical structures including
houses and industrial installations, are less affected. Because neutron radiation effects drop off very rapidly with
distance, there is a sharper distinction between areas of high lethality and areas with minimal radiation doses.
This was desired by the forces of the North Atlantic Treaty Organization (NATO), since they have to be prepared to
fight in densely populated areas; any tactical nuclear explosion will endanger civilian lives and property.
The Hydrogen Bomb: The Basics
A fission bomb, called the primary, produces a flood of radiation including a large number of neutrons.
This radiation impinges on the thermonuclear portion of the bomb, known as the secondary. The
secondary consists largely of lithium deuteride. The neutrons react with the lithium in this chemical
compound, producing tritium and helium.
This reaction produces the tritium on the spot, so there is no need to include tritium in the bomb itself. In the
extreme heat which exists in the bomb, the tritium fuses with the deuterium in the lithium deuteride.
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