Spencer L. Seager
Michael R. Slabaugh
www.cengage.com/chemistry/seager
Chapter 10:
Radioactivity and
Nuclear Processes
Jennifer P. Harris
Chapter 10 Objectives
When you have completed your study of this chapter, you should be able to:
• Describe and characterize the common forms of radiation emitted during
radioactive decay (Section 10.1; Exercise 10.2)
• Write balanced equations for nuclear reactions. (Section 10.2; Exercise 10.12)
• Define and understand the half‐life concept. (Section 10.3; Exercise 10.16)
• Describe the effects of radiation on health. (Section 10.4; Exercise 10.22)
• Describe, with examples, medical uses of radioisotopes. (Sections 10.6;
Exercise 10.30)
• Describe, with examples, nonmedical uses of radioisotopes. (Sections 10.7;
Exercise 10.36)
• Show that you understand the concept of induced nuclear reactions.
(Section 10.8; Exercise 10.38)
• Describe the differences between nuclear fission and nuclear fusion reactions.
(Section 10.9; Exercise (10.48)
RADIOACTIVE NUCLEI
• Radioactive nuclei are nuclei that undergo spontaneous
changes and emit energy in the form of radiation.
• The emission of radiation by radioactive nuclei is often
called radioactive decay.
• The intensity of radiation is unaffected by factors that
normally influence the rates of chemical reactions.
TYPES OF RADIATION
• ALPHA RADIATION
• Alpha radiation consists of a stream of particles called
alpha particles. Alpha particles are identical to helium-4
nuclei; they consist of two protons and two neutrons.
• BETA RADIATION
• Beta radiation consists of a stream of beta particles that
are identical to electrons. They are created in the nucleus
of radioactive atoms when a neutron is converted into a
proton and an electron.
• GAMMA RADIATION
• Gamma radiation consists of high energy rays similar to X
rays, but with a higher energy.
CHARACTERISTICS OF
NUCLEAR RADIATION
• The characteristics of the common types of radiation along with
the symbols used to represent them are summarized in the
following table:
EQUATIONS FOR NUCLEAR REACTIONS
• In nuclear reactions, specific isotopes of an element may
behave differently.
• For that reason, all particles involved in nuclear reactions are
designated by the notation AZ X , where X is the symbol for the
particle, A is the particle mass number, and Z is the particle
atomic number or electrical charge.
A
• The Z X notation is used for both specific isotopes and the
different types of radiation.
• The equation for a nuclear reaction is balanced when the
sum of the atomic numbers of the particles on the left side of
the equation equals the sum of the atomic numbers of the
particles on the right side, and the sum of the mass numbers
on the left side equals the sum of the mass numbers on the
right side.
EXAMPLES OF NUCLEAR REACTIONS
• Example 1: Bromine-84 decays by emitting a beta particle.
What is the symbol for the daughter produced?
84
• Solution: The symbol for bromine-84 is 35 Br . A beta
particle has a mass number (the upper number) of 0, and a
charge (the lower number) of -1. Thus, the daughter must
have a mass number of 84 and an atomic number of 36. The
element with an atomic number of 36 is krypton with a
84
symbol of 36 Kr . The balanced equation is:
84
35
Br    Kr
0
-1
84
36
EXAMPLES OF NUCLEAR REACTIONS
(continued)
• Example 2: When samarium-148 undergoes radioactive decay,
the daughter produced is neodymium-144. What kind of
radiation is emitted during the decay?
• Solution: The daughter has a mass number of 144, so the
emitted radiation must have a mass number of 4. The
difference between the atomic numbers is 2. Therefore, it is an
alpha particle. The balanced equation is:
148
62
Sm   
4
2
144
60
Nd
ISOTOPE HALF-LIFE
• The half-life of an isotope is the time required for one-half of
the radioactive nuclei in a sample of the isotope to undergo
radioactive decay.
• The half-life of an isotope is used to indicate stability. The
longer the half-life, the more stable the isotope is.
EXAMPLES OF HALF-LIVES
THE HEALTH EFFECTS OF RADIATION
• The greatest danger to living organisms of exposure to longterm, low-level radiation is the ability of high-energy or
ionizing radiation to dislodge electrons from molecules and
generate highly reactive particles called radicals or free
radicals.
• Free radicals are very reactive and may cause reactions to
occur among stable materials in the cells of organisms such
as genes and chromosomes. Such reactions might lead to
genetic mutations, cancer, or other serious conditions.
• Short-term exposure to intense radiation results in tissue
destruction in the exposed area and causes the symptoms of
acute radiation syndrome.
PROTECTION AGAINST
RADIATION EXPOSURE
• The use of shielding or distance are effective ways to prevent or
minimize the exposure of individuals to harmful radiation.
• Shielding involves the placement of dense absorbing materials
such as lead or concrete between the radiation source and
individuals.
PROTECTION AGAINST
RADIATION EXPOSURE (continued)
• Distance involves the use of the inverse square law of
radiation which is a mathematical way of saying that the
intensity of radiation is inversely proportional to the square of
the distance from the source of the radiation.
2
y
• The mathematical equation is:
x
2
y
x
• According to this equation, a doubling of the distance from a
radiation source will decrease the intensity of the radiation to
¼ the intensity at the original distance.
d
I

I
d
MEDICAL USES OF RADIOISOTOPES
• Radioactive isotopes can be detected easily in the body by
using radiation detectors.
• Radioactive isotopes and nonradioactive isotopes of the
same element undergo the same chemical reactions in the
body.
• These two characteristics make radioactive isotopes useful
as tracers in diagnostic medical work and as therapeutic
agents in some medical treatments.
TRACERS/DIAGNOSTIC USE
• Tracers are radioisotopes used medically because their
progress through the body or their localization in specific
organs can be readily followed.
• Radioisotopes used as tracers should have as many of the
following five characteristics as possible:
• Tracers should have short half-lives so they will decay
while the diagnosis is being done but will give off as little
radiation as possible after the diagnosis is completed.
• The daughter produced by the decaying tracer should be
nontoxic and give off little or no radiation of its own.
Ideally, it should be stable.
• The tracer should have a long enough half-life to allow it
to be prepared and administered conveniently.
TRACERS
• If possible, the radiation given off by the tracer should be
gamma rays because they penetrate tissue well and can
be detected readily by detectors located outside the body.
• The tracer should have chemical properties that make it
possible for the tissue being studied to either concentrate
it in diseased areas and form a hot spot or essentially
reject it from diseased areas and form a cold spot.
THERAPEUTIC USE OF RADIOISOTOPES
• Radioisotopes administered internally for therapeutic use
should have as many of the following four characteristics as
possible:
• The isotope should emit less penetrating alpha or beta
radiation to restrict damage to the target tissue.
• The isotope half-life should be long enough to allow
sufficient time for the desired therapy to be completed.
• The daughter of the isotope should be nontoxic and
should give off little or no radiation.
• The target tissue should be able to concentrate the
isotope to restrict the radiation damage to the target
tissue.
EXAMPLES OF MEDICALLY
USEFUL ISOTOPES
NONMEDICAL USES OF RADIOISOTOPES
• Many applications of radioisotopes have been made in
diverse areas, including scientific studies, industry, and
archeology.
• SCIENTIFIC STUDIES
• The study of photosynthesis in plants has been aided by
the use of radioisotopes. During photosynthesis, plants
combine carbon dioxide gas with water to form
carbohydrates like starch and cellulose. Energy to drive
the process is obtained from sunlight. The study of the
chemical pathways followed by the carbon of CO2 in
photosynthesis has been greatly aided by using CO2 that
contains radioactive carbon-14.
NONMEDICAL USES OF RADIOISOTOPES
(continued)
• ARCHEOLOGY
• The use of carbon dating to determine the age of
artifacts is indispensable in some archeology studies.
• Radioactive carbon-14 forms naturally in the atmosphere.
The radioactive carbon is converted to CO2 gas which
becomes incorporated into the cellulose of plants by
photosynthesis.
• In living plants an equilibrium exists in which the plants
contain the same fraction of radioactive carbon as the air.
When the plant is cut down, carbon dioxide intake stops
and the radioactive carbon in the plant begins to decay.
• The amount of carbon-14 in an artifact can be compared
to the amount in air. The difference and the known halflife of carbon-14 (5600 years) allows the time the carbon14 has been decaying to be calculated, which is the age
of the artifact.
NONMEDICAL USES OF RADIOISOTOPES
(continued)
• Carbon-14 dating can only be used on objects less than
about 50,000 years old.
• Other dating methods have developed.
• Potassium-40 undergoes electron capture to produce argon40.
• The half-life of potassium-40 is 1.3 x 109 years.
• By determining the amount of argon-40 in a potassiumcontaining mineral, it is possible to estimate the age of the
mineral.
40
19
K e 
0
-1
40
18
Ar
INDUCED NUCLEAR REACTIONS
• Induced nuclear reactions are reactions that take place when
nuclei are bombarded with subatomic particles such as alpha
particles or neutrons.
• An example of an induced nuclear reaction is the one that
produces radioactive carbon-14 in the atmosphere. This
process takes place when a nitrogen-14 atom is struck by a
cosmic ray neutron.
• The reaction is:
14
7
N n
1
0
14
6
C p
1
1
• Induced nuclear reactions have been used to produce all of
the transuranium elements in the periodic table (elements
with atomic numbers greater than 92).
NUCLEAR ENERGY
• Nuclear energy is released in large amounts by the
processes of nuclear fission or nuclear fusion.
• NUCLEAR FISSION
• Nuclear fission is a process in which large nuclei split
into smaller, approximately equal-sized nuclei when hit by
neutrons.
• During nuclear fission reactions, the total mass of the
products of the reaction is less than the total mass of the
reactants. The mass difference appears as energy in
agreement with Einstein's famous equation E=mc2, where
the mass difference is m and c is the velocity of light.
NUCLEAR ENERGY (continued)
• A chain reaction is a nuclear reaction in which the products
of one reaction cause a repeat of the reaction to take place.
• An expanding or branching chain reaction is a reaction in
which the products of one reaction cause more than one
more reaction to occur.
• A critical reaction
is a constant rate
reaction.
• A supercritical
reaction is a
branching chain
reaction that will
lead to an explosion.
NUCLEAR ENERGY (continued)
• A breeder reaction is a nuclear reaction in which isotopes
that will not undergo spontaneous fission are changed into
isotopes that will.
• ISSUE: can create more fuel than used up (can create a
relatively inexpensive and non-polluting energy source) vs.
fissionable product can be used for nuclear explosive devices
(can make the world a less safe place)
NUCLEAR ENERGY (continued)
• NUCLEAR FUSION
• Nuclear fusion is a process in which small nuclei combine
or fuse to form larger nuclei.
• As in nuclear fission reactions, the total mass of the
reactants is greater than the total mass of the products, and
the mass difference appears a energy in agreement with
Einstein's equation.
• A thermonuclear reaction is a nuclear fusion reaction that
requires a very high temperature to start. Research is being
done to determine the possibility as an energy source.
• The overall reaction for the energy output of the sun is:
4 H  He  2   2
1
1
4
2
0
-1