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Julien
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Chapter 16
Nuclear Radiation
Nuclear Processes
11. 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:
a. Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome
the electromagnetic repulsion between the protons.
b. Students know the energy release per gram of material is much larger in nuclear fusion or fission
reactions than in chemical reactions. The change in mass (calculated by E=mc2) is small but
significant in nuclear reactions.
c. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed
in nuclear reactions.
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.
e. Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in
matter and have different penetrations.
f. * Students know how to calculate the amount of a radioactive substance remaining after an integral
number of half-lives have passed.
g. * Students know protons and neutrons have substructures and consist of particles called quarks.
I. Natural Radioactivity.
Read Section 16.1 in your eText! I will describe alpha, beta, positron, and gamma radiation.
Do the Types of Radiation Tutorial!
A. Nuclear Stability.
1. Elements with atomic number 20 or higher usually have one or more isotopes that have unstable
nuclei.
a. An unstable nucleus is radioactive which means that it spontaneously emits small particles of
energy.
b. Radiation—
2. Radiation can take the form of alpha () and beta () particles, positrons ( +), or pure energy such
as gamma rays ().
3. Radioactive isotopes are identified by their mass number, which is written to the top left of the
element’s symbol.
a. Radioisotope—
b. The isotope is written with the name or symbol of the element with the hyphenated mass number
at the end.
B. Types of Radiation.
1. Radioactive decay is emitted from a nuclide in the form of electromagnetic emissions and/or
particles.
2. Alpha emission.
a. Alpha particle ()—
b.
3. Beta emission.
a. Beta particle ()—
b. –10 b
n ® 11 H + -10 e (b )
4. Positron Emission.
a. Positron (+)—
b.
1
1
0
1 H ® 0 n + +1 e (b +)
5. Gamma Emission.
a. Gamma rays ()—
1
0
0
-1
e +
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0
+1
e ® 2 00g
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Chapter 16 Notes from Basic Chemistry
Do the Radiation and Its Biological Effects Self Study!
C. Radiation Protection.
1. Alpha particles travel only a few centimeters in the air before they collide with air molecules,
acquire electrons, and become helium atoms.
2. Paper, clothing, and skin will protect you from alpha particles.
3. Beta particles have a very small mass and move much faster and farther than alpha particles,
traveling as much as several meters through air.
4. Beta particles can penetrate as far as 4-5 mm into the body, burning the surface of the skin, but are
stopped before reaching internal organs.
5. Heavy coats and gloves are used for protection against beta particles.
6. Gamma rays travel through the air and pass through many materials, including body tissues.
7. Gamma rays are extremely hazardous and require cement or lead to stop them.
8. The further you stay from radioactive sources, the more the protection you receive.
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Chapter 16 Notes from Basic Chemistry
Problem 1: Supply the missing information in the following table:
Medical
Use
Heart imaging
Atomic
Symbol
201
81Tl
Radiation therapy
Mass
Number
Number
of Protons
60
27
Abdominal scan
Hyperthyroidism
Leukemia treatment
31
131
53
Number
of Neutrons
36
I
32
17
You are now able to do Animation–Separation of Alpha, Beta, and Gamma Rays, and problems 16.7, 16.8,
and 16.9 in your first homework assignment and Problems 16.50 and 16.51 in your second homework
assignment.
II. Radioactive Decay.
Read Section 16.2 in your eText! I will write an equation showing mass numbers and atomic
numbers for radioactive decay.
A. Radioactive decay.
1. Radioactive decay—
a. The nuclear equation is written using the atomic symbols of the original radioactive nucleus, the
new nucleus, and the type of radiation emitted.
221
217
4
b. 87 Fr ® 85 At + 2 He
c. The sum of the mass numbers on each side are equal as is the sum of the atomic numbers on each
side.
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Chapter 16 Notes from Basic Chemistry
2. Alpha Decay happens when the mass number is reduced by four and the atomic number is reduced
by two.
Do the Writing Nuclear Equations Tutorial!
B. Guide to Completing a Nuclear Equation.
STEP 1: Write the incomplete nuclear equation.
226
88
Ra ® ? +
4
2
He
STEP 2: Determine the missing mass number.
The missing mass number is equal to the mass number of the known isotope minus the mass number
of the alpha particle.
STEP 3: Determine the missing atomic number.
The missing atomic number is equal to the atomic number of the known isotope minus the atomic
number of the alpha particle.
STEP 4: Determine the symbol of the new nucleus.
Simply look up the atomic number of the new nucleus in the Periodic Table.
STEP 5: Complete the nuclear equation.
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Chapter 16 Notes from Basic Chemistry
226
88
Ra ®
222
86
Rn +
4
2
He
Problem 2: Write a balanced nuclear equation for the alpha decay of Po–214.
C. Beta decay happens when the mass number of the radioactive nucleus and the mass number of the new
nucleus are the same and the atomic number increases by one.
1. Beta decay follows the same steps as alpha decay.
Problem 3: Write the nuclear equation for the beta decay of iodine–131.
D. Positron emission happens when a proton in an unstable nucleus is converted to a neutron and a positron
resulting in the emission of a positron while the neutron stays in the nucleus.
1. Positron emission follows the same steps as alpha decay.
Problem 4: Write the nuclear equation for xenon-118, which decays by emitting a positron.
E. Gamma emission happens as an accompaniment to most alpha and beta radiation.
1. Commonly, technetium-99m is used as a gamma emitter because it has a short half-life.
Tc ® 9943Tc + 00g
99m
43
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Chapter 16 Notes from Basic Chemistry
F. Producing radioactive isotopes.
1. Commonly, technetium-99m is used as a gamma emitter because it has a short half-life.
2. Radioisotopes can be made by a process named transmutation, where a stable nucleus is bombarded
by a high-speed particle, such as alpha particles, protons, neutrons and other small nuclei.
3. All elements over element 92 have been produced by bombardment and most only last a fraction of a
second and only produce a few particles.
4. Technetium-99m is produced in laboratories which have small generators stocked with molybdenum
-99, which will decay into technetium-99m.
5. The pathway for making Tc-99m:
1
0
n +
99
42
98
42
Mo ®
Mo ®
Tc ®
99m
43
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99m
43
99
42
Tc +
Mo
0
-1
Tc + 00g
99
43
e
(At the reactor)
(At the laboratory generator)
(In the patient)
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Chapter 16 Notes from Basic Chemistry
Problem 5: Complete the following bombardment equation:
4
2
He + ? ® 178 O + 11 H
You are now able to do Problems 16.14, 16.16, 16.20, and 16.22 in your first homework assignment and
Problems 16.57, 16.58, 16.59, 16.60, and 16.61 in your second homework assignment.
III. Radiation Measurement.
Read Section 16.3 in your eText! I will describe the detection and measurement of radiation.
A. Measuring radiation.
1. Measurement of radioisotopes is done based on the number of nuclear disintegrations per second.
a. Curie (Ci)—
b. Becquerel (Bq)—
c. Rad (Radiation Absorbed Dose)—
d. Gray (Gy)—
e. Rem (Radiation Equivalent in humans)—
f. Alpha particles can only do damage to you when they get inside but beta particles, and highenergy protons and neutrons can travel into tissue and do damage.
g. Gamma rays can easily penetrate the skin and do damage to body tissue.
h. Equivalent dose—
Biological damage (rem) = Absorbed dose (rad) x Factor
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Chapter 16 Notes from Basic Chemistry
i. Sievert (Sv)—
Do the Food Irradiation Case Study!
Problem 6: An iodine–131 source has an activity of 0.25 Ci. How many radioactive atoms will
disintegrate in 1.0 min?
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Chapter 16 Notes from Basic Chemistry
B. Exposure to radiation.
1. We are exposed to low levels of radiation daily.
2. Common radioisotopes are potassium-40 which is found in food,
carbon-14, radon-222, strontium-90, and iodine-131 are found in the
air and in food.
3. Typically, the average person in the US receives 260 mrem of
radiation per year.
4. If you live at high altitudes or travel by airplane, you will receive a
greater amount of cosmic radiation.
5. Living in Denver, you would receive twice the radiation as you would
if you lived in Los Angeles.
6. Living near a nuclear power plant adds 0.1 mrem in one year with the
people of Chernobyl receiving as much as 1 rem/hour.
C. Radiation sickness.
1. Exposure to radiation less than 25 rem usually cannot be detected.
2. Whole-body exposure of about 100 rem reduces the white blood cell
count temporarily.
3. Exposure to more than 100 rem can cause nausea, fatigue, and a
reduction in white-cell count.
4. Exposure to more than 300 rem can drop the white-cell count to zero,
and can cause diarrhea, hair loss, and infection.
5. Exposure to more than 500 rem can cause death in 50% of the people
receiving that dose.
6. LD50 is a term for a dose where 50% of the population will die as a
result of the exposure.
7. Radiation doses of 600 rem would be fatal to all humans within a few
weeks.
You are now able to do Measuring Radiation Tutorial in your first homework assignment.
IV. Half-life of a radioisotope.
Read Section 16.4 in your eText! Given the half-life of a radioisotope, I will calculate the
amount of radioisotope remaining after one or more half-lives.
Do the Nuclear Chemistry Self Study Activity!
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Chapter 16 Notes from Basic Chemistry
A. Half-life—
B. If only the radioactive isotopes can decay and become stable when they do, the remaining isotopes
which haven’t decayed have the same chance to decay in an equal period of time.
C. Decay curve—
Problem 7: Iron–59 has a half-life of 44 d. If a nuclear laboratory receives a sample of 32 g of iron-59,
how many micrograms of iron-59 remain after 176 d?
Do the Radioactive Half-Lives Tutorial!
Problem 8: Suppose that a piece of wood found in a tomb had 1/8 of its original carbon-14 activity. About
haw many years ago was the wood part of a living tree?
You are now able to do Radioactive Half-lives Tutorial and Radiocarbon Dating Tutorial in your first
homework assignment.
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Chapter 16 Notes from Basic Chemistry
V. Medical Applications Using Radioactivity.
Read Section 16.5 in your eText! I will describe the use of radioisotopes in medicine.
A. Scans with radioisotopes.
1. A scanner is used once the injected or ingested radioisotope has had time to migrate to the target
organ or system.
2. The radiologist uses the scanner to detect the gamma rays emitted from the radioisotope and
produces an exposed photographic plate.
3. Areas of decreased or increased radiation can indicate a disease, a tumor, a blood clot or an edema.
4. Ingestion of I-131 can be used to see how much iodine is taken in by a thyroid gland which can
indicate hyperthyroidism if more is taken in than normal.
5. A larger dose of iodine can be used to destroy some of the cells in the thyroid gland and reduce
hormone production.
B. Positron Emission Tomography (PET)
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Chapter 16 Notes from Basic Chemistry
1. Carbon-11, oxygen-15, nitrogen-13, and fluorine-18 are used as positron emitters because they have
short half-lives.
2. The addition of glucose to fluorine-18 allows scientists to study brain function, metabolism, and
blood flow.
3. As positrons are emitted, they combine with electrons to produce gamma rays that are detected by
computerized equipment in a three-dimensional image of the organ.
18
9
F ®
18
8
O +
0
+1
e then,
0
-1
e +
0
+1
e ® 2 00g
The above PET scan shows a normal brain on the left and a brain affected by Alzheimer’s disease on the right.
Problem 9: In an experimental treatment, a person is given boron-10, which is taken up by malignant
tumors. When bombarded with neutrons, boron-10 decays by emitting alpha particles that
destroy the surrounding tumor cells. Write the nuclear equation for the experimental
procedure.
C. Computed tomography (CT) uses a computer to monitor the degree of absorption of 30,000 X-ray beams
directed at successive layers of tissue, comparing the difference in absorption of those layers.
Note the tumor (yellow
mass) on the right side of
the brain.
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Chapter 16 Notes from Basic Chemistry
D. Magnetic Resonance Imaging (MRI) is based on the absorption of energy when protons in hydrogen
atoms are excited by a strong magnetic field.
1. Hydrogen atoms make up 63% of the atoms in the body and can be oriented in one direction by a
strong magnetic field.
2. Radiofrequency pulses are applied and it causes protons to flip and become aligned against the field.
3. Because the protons are in various chemical relationships throughout the body, different energies are
absorbed and the computer assigns different colors to the different frequencies, producing a color
read out of different parts of the body.
You are now able to do Problem 16.65 in your second homework assignment.
VI. Nuclear Fission and Fusion.
Read Section 16.6 in your eText! I will describe process of nuclear fission and fusion.
A.Nuclear fission.
1. Fission—
2. The mass of the starting materials is less than the mass of the end products, producing a situation
called a mass defect.
3. Albert Einstein discovered that the defect was predictable and generated his famous equation, E =
mc2, to explain the large amount of energy released from the process.
4. E is the energy released, m is the mass lost, and c is the speed of light (3 x 108 m/s).
5. The fission of one gram of uranium-235 produces about as much energy as the burning of three tons
of coal.
B. Chain Reaction.
1. Fission begins when a neutron collides with the nucleus of a uranium-235 atom resulting the split of
the unstable nucleus into two smaller nuclei.
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Chapter 16 Notes from Basic Chemistry
2. The split releases several neutrons and a large amount of gamma radiation.
3. If more uranium-235 nuclei are near, the additional high-energy neutrons can collide with them and
cause more splits.
4. Chain reaction—
5. The reaction is sustained if there are enough nuclei close together; a situation called a critical mass.
C. Nuclear Fusion.
1. Fusion—
2. Mass is lost and a tremendous amount of heat is released when the temperature reaches 100,000,000
°C.
3. The sun fuses 6 x 1011 kg of hydrogen every second and has been doing so for 4.6 billion years.
4. Fusion produces less radioactive waste but is too hot to contain the reaction in a vessel.
You are now able to do Problems 16.41 and 16.42 in your second homework assignment.
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Chapter 16 Notes from Basic Chemistry