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Chapter 10
The Nucleus,
Radioactivity, and
Nuclear Medicine
Denniston
Topping
Caret
4th Edition
10.1 Natural Radioactivity
• Radioactivity – process by which atoms
emit energetic particles or rays.
• Radiation – the particles or rays emitted.
– comes from the nucleus
• Nuclear symbols – what we use to
designate the nucleus.
– Atomic symbol
– Atomic number
– Mass number
10.1 Natural Radioactivity
mass number
number of
protons and
neutrons
11
5
B
atomic symbol
atomic number
number of
protons
• This symbol is the same as writing
boron-11.
10.1 Natural Radioactivity
11
5
B
• Remember for section 2.2, this defines an
isotope of boron.
• In nuclear chemistry this is often called a
nuclide.
• This is not the only isotope (nuclide) of
boron.
– boron-10 also exists
– How many protons and neutrons does
boron-10 have?
– 5 protons, 5 neutrons
10.1 Natural Radioactivity
• Some isotopes are stable
• The unstable isotopes are the ones that
produce radioactivity.
• To write nuclear equations (section 10.2)
we need to be able to write the symbols
for the isotopes and the following:
– alpha particle
– beta particles
– gamma rays
10.1 Natural Radioactivity
Alpha Particles
1
• Alpha particle (a) – 2 protons, 2
neutrons.
• Same as He nucleus (He2+)
• Slow moving, and stopped by small
barriers.
• Symbolized in the following ways:
4
2
He
2
4
2
He
α
4
2
α
10.1 Natural Radioactivity
Bata Particles
1
• Beta particles (b) – fast-moving
electron.
• Emitted from the nucleus as a
neutron is converted to a proton.
• Higher speed particles, more
penetrating than alpha particles.
• The symbol is…
0
1
e
0
-1
β
β
10.1 Natural Radioactivity
Gamma Rays
1
• Gamma Rays (g) – pure energy
(electromagnetic radiation.)
• Highly energetic, the most penetrating
form of radiation.
• Symbol is simply…
g
10.1 Natural Radioactivity
Properties of Alpha, Beta, and
Gamma Radiation
1
• Ionizing radiation – produces a trail of
ions throughout the material that it
penetrates.
• The penetrating power of the radiation
determines the ionizing damage that
can be caused.
• Alpha particle < beta particle < gamma
rays.
10.2 Writing a Balanced Nuclear
Equation
• Nuclear equation - used to represent
nuclear change.
• In a nuclear equation, you do not balance
the elements, instead...
– the total mass on each side of the reaction
arrow must be identical
– the sum of the atomic numbers on each side of
the reaction arrow must be identical
2
10.2 Writing Balanced
Nuclear Equations
Alpha Decay
238
92
U
238
92
Th  He
234
90
4
2
= 234 +
mass number
=
90 +
atomic number
4
2
10.2 Writing Balanced
Nuclear Equations
Beta Decay
16
7
N O  e
16
8
0
-1
10.2 Writing Balanced
Nuclear Equations
Gamma Production
• Gamma radiation occurs to increase the
stability of an isotope.
– The energetically unstable isotope is
called a metastable isotope.
• The atomic mass and number do not
change.
Tc 
99m
43
Tc  g
99
43
• Usually gamma rays are emitted along with
alpha or beta particles.
10.2 Writing Balanced
Nuclear Equations
Predicting Products of Nuclear Decay
• To predict the product, simply remember
that the mass number and atomic number
is conserved.
239
92
UX e
0
-1
• What is the identity of X?
239
Np
93
10.3 Properties of Radioisotopes
Nuclear Structure and Stability
• Binding Energy - the energy that holds the
protons, neutrons, and other particles
together in the nucleus.
• Binding energy is very large.
• When isotopes decay (forming more stable
isotopes,) binding energy is released.
10.3 Properties of
Radioisotopes
• Important factors for stable isotopes.
– Ratio of neutrons to protons.
– Nuclei with large number of protons (84 or
more) tend to be unstable.
– The “magic numbers” of 2, 8, 20, 50, 82, or
126 help determine stability. These numbers
of protons or neutrons are stable.
– Even numbers of protons or neutrons are
generally more stable than those with odd
numbers.
– All isotopes (except 1H) with more protons
than neutrons are unstable.
10.3 Properties of
Radioisotopes
Half-Life
3
• Half-life (t1/2) - the time required for onehalf of a given quantity of a substance to
undergo change.
• Each radioactive isotope has its own
half-life
– Ranges from a fraction of a second to a
billion years.
– The shorter the half-life, the more unstable
the isotope.
10.3 Properties of
Radioisotopes
10.3 Properties of
Radioisotopes
A patient receives 10.0 ng of a radioisotope
with a half-life of 12 hours. How much will
remain in the body after 2.0 days, assuming
that radioactive decay is the only path for
removal of the isotope form the body.
10.4 Nuclear Power
4
Energy Production
E = mc2
• Equation by Albert Einstein shows the
connection between energy (E) and the mass
(m)
• c is the speed of light
• The equation shows that a very large amount
of energy can be formed from a small amount
of matter.
10.4 Nuclear Power
Nuclear Fission
• Fission (splitting) occurs when a heavy
nuclear particle is split into smaller nuclei
by a smaller nuclear particle.
1
0
n
235
92
U
236
92
U
92
36
Kr 
Ba  3 n  energy
141
56
1
0
• Accompanied by a large amount of energy.
• Is self perpetuating.
• Can be used to generate steam.
10.4 Nuclear Power
• Chain reaction - the reaction sustains
itself by producing more neutrons
10.4 Nuclear Power
• A nuclear power plant uses a fissionable
material as fuel.
– Energy released by the fission heats water
– produces steam
– drives a generator or turbine
– converts heat to electrical energy
10.4 Nuclear Power
Nuclear Fusion
• Fusion (to join together) - combination of
two small nuclei to form a larger nucleus.
• Large amounts of energy is released.
• Best example is the sun.
• An Example:
2
1
H  H  He  n  energy
3
1
4
2
1
0
• No commercially successful plant exists in
U.S.
10.4 Nuclear Power
Breeder Reactors
• Breeder reactor - fission reactor that
manufactures its own fuel.
• Uranium-238 (non fissionable) is
converted to plutonium-239
(fissionable).
• Plutonium-239 undergoes fission to
produce energy.
10.5 Radiocarbon Dating
5
• Radiocarbon dating - the estimation of the
age of objects through measurement of
isotopic ratios of carbon.
– Ratio of carbon-14 and carbon-12
• Basis for dating:
– Carbon-14 (a radioactive isotope) is constantly
being produced by neutrons from the sun.
14
7
N n C H
1
0
14
6
1
1
10.5 Radiocarbon Dating
• Living systems are continually taking in
carbon.
– The ratio of carbon-14 to carbon-12 stays
constant during its lifetime.
• Once the living system dies, it quits
taking in the carbon-14.
– The amount of carbon-14 decreases
according to the reaction:
14
6
C N e
14
7
0
-1
• The half-life of carbon-14 is 5730 years.
– This information is used to calculate the age.
10.6 Medical Applications of
Radioactivity
• Modern medical care uses the following:
– Radiation in the treatment of cancer.
– Nuclear medicine - the use of radioisotopes in
the diagnosis of medical conditions.
6
10.6 Medical Applications
Cancer Therapy Using Radiation
7
• Based on the fact that high-energy
gamma rays cause damage to biological
molecules.
• Tumor cells are more susceptible than
normal cells.
• Example: cobalt-60
• Gamma radiation can cure cancer but
can also cause cancer.
10.6 Medical Applications
Nuclear Medicine
• The use of isotopes in diagnosis.
• Tracers - small amounts of radioactive
substances used as probes to study internal
organs.
• Nuclear imaging - medical techniques
involving tracers.
• Example:
– Iodine concentrates in the thyroid gland.
– Using radioactive 131I and 125I will allow the
study of how the thyroid gland is taking in
iodine.
10.6 Medical Applications
• Isotopes with short half-lives are preferred
for tracer studies. Why?
– They give a more concentrated burst.
– They are removed more quickly from the
body.
• Examples of imaging procedures:
– Bone disease and injury using technetium99m
– Cardiovascular disease using thallium-201
– Pulmonary disease using xenon-133
10.6 Medical Applications
Making Isotopes for Medical Applications
• Artificial radioactivity - a normally 8
stable, nonradioactive nucleus is made
9
radioactive.
• Made in two ways:
• In core of a nuclear reactor
• In particle accelerators - small nuclear
particles are accelerated to speeds
approaching the speed of light and
slammed into another nucleus.
10.6 Medical Applications
Examples of artificial radioactivity:
197
79
Au  n 
1
0
198
79
Au
• Tracer in the liver
66
30
Zn  p 
1
1
67
31
Ga
• Used in the diagnosis of Hodgkin’s
disease.
10.6 Medical Applications
• Some isotopes used in nuclear medicine
have such a short half-life that they need
to be generated on site.
•
99mTc
has a half-life of only 6 hours.
99
42
Mo 
Tc  e
99m
43
0
-1
10.7 Biological Effects of
Radiation
10
Radiation Exposure and Safety
The Magnitude of the Half-Life
• Isotopes with short half-lives have one major
disadvantage and one major advantage.
– Disadvantage: larger amount of radioactivity per
unit time.
– Advantage: if accident occurs, reaches
background radiation levels more rapidly
10.7 Biological Effects
Shielding
• Alpha and beta particles need low level
of shielding (lab coat and gloves.)
• Lead, concrete or both required for
gamma rays.
Distance from the Radioactive Source
• Doubling the distance from the source
decreases the intensity by a factor of 4.
10.7 Biological Effects
Time of Exposure
• Effects are cumulative
Types of Radiation Emitted
• Alpha and beta emitters are generally
less hazardous then gamma emitters.
Waste Disposal
• disposal sites are considered temporary.
10.8 Measurement of Radiation 11
Nuclear Imaging
• Isotope is administered.
• Isotope begins to concentrate in the organ.
• Photographs (nuclear images) are taken at
periodic intervals.
• Emission of radioactive isotope creates the
image.
10.8 Detection and
Measurement of Radiation
Computer Imaging
• Computers and television are coupled
• Gives a continuous and instantaneous
record of the voyage of the isotope
throughout the body.
– Gives increased sensitivity
– CT scanner is an example
10.8 Detection and
Measurement of Radiation
The Geiger Counter
• Detects ionizing radiation
• Has largely been replaced by more
sophisticated devises.
10.8 Detection and
Measurement of Radiation
Film Badges
• A piece of photographic film that is
sensitive to energies corresponding to
radioactive emissions.
• The darker the film, when developed,
the longer the worker has been
exposed.
10.8 Detection and
Measurement of Radiation
Units of Radiation Measurement
12
The Curie
• The amount of radioactive material
that produces 3.7 x 1010 atomic
disintegrations per second.
• Independent of the nature of the
radiation
10.8 Detection and
Measurement of Radiation
The Roentgen
• The amount of radiation needed to
produce 2 x 109 ion pairs when passing
through one cm3 of air at 0oC.
• Used for very high energy ionizing
radiation only.
10.8 Detection and
Measurement of Radiation
Rad
• Radiation absorbed dosage.
• The dosage of radiation able to transfer
2.4 x 10-3 cal of energy to one kg of
matter.
• This takes into account the nature of
the absorbing material.
10.8 Detection and
Measurement of Radiation
The Rem
• Roentgen Equivalent for Man
• Obtained by multiplication of the rad by a
factor called the relative biological effect
(RBE)
• RBE = 10 for alpha particles
• RBE = 1 for beta particles
• Lethal dose (LD50) - the acute dosage of
radiation that would be fatal for 50% of the
exposed population.
• LD50 = 500 rems.
The End
Chapter 10