Teacher’s Resource
AUTHORS
Barry LeDrew
Jim Axford
Allan Carmichael
Doug Fraser
Karen Morley
John Munro
Darrell Scodellaro
PROGRAM CONSULTANT
Barry LeDrew
UNIT
C
Radioactivity
Contents
Lesson Plans
Chapter 10: Radioactivity and the Atom
10.1 Radioactivity and its History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
10.2 Radioactivity and the Nucleus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.3 Radioactive Decay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Investigation 10A Penetrating Ability of Nuclear Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.4 Half-Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Investigation 10B The Half-Life of Popcorn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Chapter 10 Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Chapter 10 Blackline Masters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
BLM 10.3-1 Alpha, Beta and Gamma Decay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
BLM 10.3-2 Writing Nuclear Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
BLM 10.4-1 Radioactive Decay and Half-Life. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
BLM 10.4-2 Radioactivity Concept Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Chapter 10: Blackline Masters and Worksheets Answer Key. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
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Contents
iii
CHAPTER
10
Radioactivity and the Atom
Key Ideas
Vocabulary
Atoms of a single element that differ in mass
are called isotopes.
radioactivity
nucleus
proton
neutron
isotope
radioactive decay
parent nucleus
The atoms of some elements are radioactive,
which means that they undergo radioactive
decay.
There are three basic types of radioactive
decay and these processes can be written as
nuclear equations.
Page 274
daughter nucleus
alpha particle ()
beta particle ()
gamma ray ()
half-life
decay series
The rate of decay of a radioactive sample is
predictable and is described by the half-life of
the radioactive isotope.
TEACHING NOTES
• Possible Misconceptions
– Identify: Students may think that radiation is something given off by a few
dangerous materials confined to scientific or medical laboratories or
nuclear power plants.
– Clarify: Explain to students that living things are exposed constantly to
background radiation from both natural and human-made sources. Point
out that radioactive isotopes exist throughout nature in rocks, soils, water,
plants, and even in our own bodies. Human-made sources of background
radiation include televisions, computers, and some medical equipment.
Remind students that low levels of natural background radiation are
generally not harmful.
– Ask What They Think Now: Ask, How has your understanding of the sources
of radiation changed?
Related Resources
B.C. Probe 10
Computerized
Assessment Bank
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
Thomson Gale Science
Resource Center
Nelson Science Probe 10
Website
www.science.nelson.com
• To gauge prior knowledge, ask students where they have heard or seen
references to radiation or radioactivity before. For most students, radiation
and radioactivity have negative connotations. Tell them to keep note of
if/how their perceptions change as they study this chapter.
• Many people have concerns about exposure to radiation from nuclear power
plants, especially after the well-publicized incidences at Three Mile Island
and Chernobyl. High doses of radiation or prolonged exposure can be
dangerous to humans and other living things. Reassure students, however,
that the background radiation to which humans are exposed is generally not
at a harmful level. Point out that, overall, nuclear power plants have excellent
safety records.
• Carry out with students Try This: Radioactivity All Around Us.
Technology Connections
Explain to students that
many countries rely on
nuclear power for
generation of electricity.
Point out that in 2002,
nuclear power provided
13 % of Canada’s
electricity.
• Information is available on the Nelson Science website wherever a Go icon
appears in the Student Book.
NEL
Chapter 10 Radioactivity and the Atom
1
• Multimedia activities are available on the Nelson Science website whenever a
green Multimedia icon appears in the Student Book.
• As you progress through the chapter, prompt students to make study notes
in the Study Guides found in the Student Workbook.
TRY THIS: RADIOACTIVITY ALL AROUND US
Purpose
• Students examine everyday sources of radiation.
Notes
• Materials: Geiger counter, glass crystal, pottery glaze, smoke detector, wristwatch
• Assign a student volunteer to be the timekeeper for the demonstration.
• Note that the wristwatch used should be an analog type watch with a glowing hand. These glowing hands are
painted with tritium. A digital watch or an analog watch without a glowing hand will not produce detectable
radiation.
Suggested Answers
A. The smoke detector had the highest number of counts per minute. The glass had the lowest.
B. It would be more accurate to record the number of counts per hour and divide to get the number of counts per
minute. Averages are generally more accurate with a larger sample size. However, extrapolating from number
of counts per minute is probably a reasonable method.
Meeting Individual Needs
ESL
• Have students create idea webs in response to the question about where or what they have heard about
radiation and radioactivity. Allow them to use sketches, single words, or simple phrases in their webs. Tell
them to keep their idea webs so they can revise them with more sketches, words, or phrases at the end of
the chapter.
Extra Support
• Provide guidance for the Try This activity. Have them write Many counts, more radiation and Few counts, less
radiation above their data tables as a reminder. To reinforce the take-home message of the activity for
students, ask them to make a conclusion about whether humans can avoid all radiation. (no; There is
always some background radiation. Many everyday objects give off radiation.)
Extra Challenge
• Have students work in small groups to research the nuclear power plant incident that occurred at Three
Mile Island in March 1979 or in Chernobyl in April 1986. Have them act in the role of newspaper
reporters to produce brief news accounts describing what happened.
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Unit C: Radioactivity
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10.1 Radioactivity and its History
Page 275
PRESCRIBED LEARNING OUTCOMES
Time
• explain radioactivity using modern atomic theory
• demonstrate scientific literacy
• describe the relationship between scientific principles and technology
30–45 min
Key Ideas
The atoms of some elements
are radioactive, which means
they undergo radioactive
decay.
KNOWLEDGE
• radioactivity
• application of scientific principles in the development of technologies
Vocabulary
SKILLS AND ATTITUDES
• acquire and apply scientific and technological knowledge to the benefit of
self, society, and the environment
• demonstrate competence in using basic information technology tools
SCIENCE BACKGROUND
• Electromagnetic radiation occurs
when an atom emits a photon.
• Electromagnetic radiation has the
properties of both waves and
particles.
• Photons have different energy levels
and wavelengths.
• Low-energy photons produce
familiar, harmless radiation such as
radio waves and visible light. Highenergy photons are more harmful
and include X-rays and ultraviolet
light.
• It is important to note that the term
radiation can refer to
electromagnetic radiation, but it can
also refer to the emission of
NEL
Program Resources
WS 10.1-1 Study Guide
WS 10.2-2 Radioactivity and
its History
Nelson Science Probe 10
Website
www.science.nelson.com
ICT OUTCOMES
Electromagnetic Radiation
• Electromagnetic radiation is
essentially another term for light. In
addition to visible wavelengths of
light, however, it also includes
energy of shorter wavelengths such
as X-rays and gamma rays, and
longer wavelengths such as infrared
and radio waves.
• radioactivity
subatomic particles such as protons
and neutrons.
Electricity and Magnetism
• Electricity and magnetism are similar
in that they both involve the
interactions of particles with force
fields, or regions of space in which
objects feel a force. Electric fields
can affect electrically charged
objects, and magnetic fields can
affect magnetically susceptible
objects. Electricity and magnetism
are also related in another way. A
moving electric charge can produce
a magnetic field, and a moving
magnet can produce an electric field.
Electric generators and electric
motors make use of this relationship.
In an electric generator, mechanical
energy is used to turn a magnet,
which produces an electric field and
so generates electricity in a wire. In
an electric motor, electric current
flows near a magnet and causes the
magnet to move. The motion of the
magnet powers the motor.
Related Resources
McClafferty, Carla Killough.
Something Out of
Nothing: Marie Curie and
Radium. Farrar, Straus,
and Giroux Books for
Young Readers, 2006.
B.C. Probe 10
Computerized
Assessment Bank
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
Thomson Gale Science
Resource Center
Nelson Science Probe 10
Website
www.science.nelson.com
Animations
– Cathode rays
Chapter 10 Radioactivity and the Atom
3
TEACHING NOTES
1 Getting Started
• Teacher Demo: Visualising Radiation
– Give students or pairs of students a sheet of photosensitive paper.
Photosensitive paper is available from science education suppliers. Be
sure to keep the paper away from direct light.
– In a dimly lit room, have the students place two to five objects of
varying sizes and shapes on the sheet of paper.
– When the students have finished placing their objects on the paper, open
windows to let sunlight into the room or allow students to carefully take
their papers outside for five minutes.
– After a few minutes, the paper should begin to react to the sunlight.
Follow the directions on the packaging to set the image.
– After students have finished their images, ask them to speculate as to
how the image-making process might have worked. Encourage students
to follow lines of reasoning that led them to the basic concepts of
radioactivity, such as light from the Sun carrying energy that affects the
photosensitive paper.
Social Studies
Connections
Though radiation in small
doses is not harmful, in
large amounts, it can be
devastating. Have students
research the 1986 accident
at the Chernobyl nuclear
power station. Have them
write a summary of the
effects of radioactive
emissions on that city to
this day.
• Possible Misconceptions
– Identify: (a) Students might think that all radiation is harmful.
(b) Some students may think that all forms of radiation are made by
people.
– Clarify: (a) Most kinds of radiation, such as radio waves, visible light,
and infrared light, are not harmful to humans. Higher energy radiation,
including microwaves, ultraviolet rays, X-rays, and gamma rays, can be
harmful to humans. However, these forms of radiation are generally
harmful only if humans are exposed to large amounts of them at once,
or to low levels of them for a long time. In fact, small targeted doses of
high-energy radiation can destroy or shrink tumors and other harmful
growths. Radiation in small doses is also used in radiographs (X-rays)
and CAT scans that doctors rely on when diagnosing diseases.
(b) Many natural materials produce radiation. The Sun is a source of
radiation. Uranium, radium, plutonium, and polonium, which are used
in some technologies, are examples of naturally occurring radioactive
elements. Some kinds of rock, such as granite, produce small amounts of
radiation because of the elements in them.
– Ask What They Think Now: (a) Ask, If someone in your family stated that
all radiation is harmful, how would you respond to that statement? Students
should be able to explain that many forms of radiation are not harmful,
even in large doses. Students should also be able to explain clearly that
although radiation can be harmful, when it is carefully controlled it is an
essential medical tool.
(b) Ask students to think about natural sources of radiation exposure in
their lives. Ask, How does your lifestyle and where you live affect your
exposure to naturally occurring radiation?
2 Guide the Learning
• This section provides background for students to understand the events
leading to the discovery of radioactivity. Students may not realize that
radioactivity is a relatively recent discovery compared to discoveries in
4
Unit C: Radioactivity
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other areas of science. This section also lays the groundwork for an
understanding of the many contemporary uses of radiation.
• As students examine Figure 2, remind them that electricity and magnetism
are related. In the figure, the beam in the cathode-ray tube bends because
of a pair of electrically charged deflection plates. A magnet would produce
a similar effect.
3 Consolidate and Extend
• Discuss the everyday applications of radiation. Encourage students to
think of careers that involve working with radiation (such as a radiologist
or a radiology technician).
• Have students engage in debate. Some students should argue for the
beneficial uses of radiation therapy, and others should argue against the use
of technology that may cause some people to be exposed to large amounts
of radiation. Consider having students record the key points in the debate
and then repeat the debate later in the unit after working through section
11.1. Have students compare the points made in the two debates.
• Have students complete the Check Your Understanding questions.
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. The wavelength decreases.
2. X-rays have shorter wavelengths, higher frequencies, and greater energy than visible light waves.
3. Scientists once thought that gases were poor conductors of electricity, but during the mid-to-late 1800s,
scientists learned that gas in a partial vacuum would conduct electricity well.
4. Atomic nuclei can produce several kinds of electromagnetic radiation, including X-rays and gamma rays.
5. An electron beam will bend away from a negatively charged plate and toward a positively charged plate.
Therefore, the plate toward which the beam in the diagram is bending must be the positively charged plate.
6. Scientists put a small paddle-wheel in a cathode ray. The ray caused the wheel to spin, indicating that cathode
rays are made of particles.
7. Students can infer that since cathode-ray tubes produce X-rays, Crookes tubes probably do also. X-rays can be
harmful in large doses, so students should stand several meters away to reduce their exposure.
8. (a) The electron’s speed will decrease extremely rapidly.
(b) The energy in the X-ray comes from the electron, which loses energy when it slows down. The electron’s
kinetic energy has been converted into the energy of radiation.
9. Visible light has a longer wavelength, a lower frequency, and less energy than an X-ray has. Both are forms of
energy called electromagnetic radiation: both travel as waves at the speed of light (through a vacuum)
10. X-rays will expose photographic film. They can travel through soft materials, such as paper and skin, but not
hard materials, such as jewellery and bone. To create an X-ray image, X-rays are fired at something, such as a
human hand, that is in front of a plate containing photographic film. When the film is developed, the X-rays will
have exposed all the areas where they can penetrate and will have left unexposed all the areas they cannot
penetrate.
11. radium and polonium
12. Radioactivity: when an atom releases radiation from its nucleus
13. Temperature, pressure, and chemical changes do not affect the amount of radiation emitted by a radiation
source.
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Chapter 10 Radioactivity and the Atom
5
Strategies for Success
Making Study Cards
• Ask students to pay close attention to the sequence of events described on pages 275 and 276 in the
Student Book. Tell them to think about the event that allowed another event to take place as they read.
Students who have trouble memorizing a sequence of events might benefit from kinesthetic learning
methods. Have students make study cards for the material in this section so that they can manipulate the
events in the sequence. Each card should have the name of a scientist on one side of a card and the
appropriate discovery on the other. After students make their study cards, encourage them to lay the cards
out in the appropriate sequence. Then have students use their study card timelines to talk with a partner
about how each discovery built on another. The cards can also be used as flash cards to prepare for an exam.
Meeting Individual Needs
ESL
• Students may look automatically for cognates to relate difficult science terms to similar words they already
understand. Cognates are words that are related because they were derived from the same source. For
instance, they may try to make the connection between radio and radioactivity. If you notice students
forming a connection that is not helpful to their understanding of the concepts, explain that these words
are only very loosely related and then guide them to a more appropriate connection in the text, such as rays
and radiate for radioactive.
Extra Support
• Students may envision parts of the electromagnetic spectrum as distinctly different things, and they may
have difficulty understanding that the division between various types of electromagnetic radiation (and
between various colors of visible light) is not clear-cut. Have students study Figure 6. Then ask then what
they think the wavelengths between ultraviolet light and X-rays might be. Guide them to the concept that
the electromagnetic spectrum is a continuum with no distinct dividing lines.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Evidence that students can
• identify the parts of a cathode-ray tube
• explain why a beam of electrons in a cathode-ray tube may be deflected in one direction or another
• explain several contemporary uses for radiation and radioactivity
• describe safety procedures taken by professionals who work with radioactive substances
• describe the electromagnetic spectrum
• define radioactivity
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Unit C: Radioactivity
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10.2 Radioactivity and the Nucleus
PRESCRIBED LEARNING OUTCOMES
Page 280
Time
• explain radioactivity using modern atomic theory
• represent and interpret information in graphic form
30–45 min
Key Ideas
KNOWLEDGE
Atoms of a single element
that differ in mass are called
isotopes.
• radioactivity
SKILLS AND ATTITUDES
Vocabulary
• use the periodic table and ion charts
• use models to demonstrate how systems operate
•
•
•
•
SCIENCE BACKGROUND
Isotope Symbols
• Throughout the chapter, atomic
number (A) is given along with the
chemical symbol and mass number
(Z ). Because all atoms of the same
element have the same number of
protons, atomic number can be
identified from the chemical symbol
using the periodic table. Including
atomic number is a convenience that
allows students to see more clearly
the relationship between isotopes of
an element and to solve nuclear
equations more easily. Typically,
however, atomic number is not
displayed.
Program Resources
Detecting Neutrons
• The main way humans detect matter
is through use of visible light, electric
fields, and magnetic fields.
Neutrons, like all subatomic particles
are too small to see. Because they
are neutral, they are unaffected by
electric fields or magnetic fields.
These challenges made detection of
the nucleus difficult.
WS 10.2-1 Study Guide
WS 10.2-2 Radioactivity and
the Nucleus
Nelson Science Probe 10
Website
www.science.nelson.com
Related Resources
“Islands of Stability.”
NOVA scienceNOW.
NOVA, 2006. Video
B.C. Probe 10
Computerized
Assessment Bank
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
TEACHING NOTES
1 Getting Started
Thomson Gale Science
Resource Center
• Teacher Demo: Rutherford Experiment Analogy
• Draw a dot about the size of a coin on the board. Stand at the opposite
end of the room. Ask students to consider the following thought
experiment: If you were to fire a grain of salt toward the board from where
you were standing, how likely is it that the salt grain would hit the spot on
the board? Allow students to respond.
• Then ask them to consider what would happen if the spot were the size of
the board or if the board were filled with many of the smaller dots. Ask,
Would you be more likely or less likely to hit a spot with the grain of salt?
Allow students to discuss briefly.
• Explain the analogy for students as it relates to what Rutherford observed.
Tell students that the grain of salt represents a positively charged particle in
Rutherford’s experiment and that the small spot on the board represents
the nucleus of an atom. Note that the items chosen to represent parts of
the atom are not meant to suggest an actual size or distance scale.
NEL
nucleus
proton
neutron
isotope
Nelson Science Probe 10
Website
www.science.nelson.com
Animations
– The Rutherford
experiment
Chapter 10 Radioactivity and the Atom
7
• Possible Misconceptions
– Identify: When students hear the word nucleus, they might think of the
nucleus of a cell, equating the two structures.
– Clarify: The word nucleus is used to describe two very different structures.
The nucleus of a cell contains the cell’s genetic material (DNA). The
nucleus of an atom is made up of the atom’s protons and neutrons. An
atom is orders of magnitude smaller than a cell. In fact, a single cell can be
made up of trillions of atoms. Explain that the word nucleus comes from a
Latin word meaning “kernel” and refers to the central or important part of
something.
– Ask What They Think Now: Ask, How is the nucleus of a cell different from
the nucleus of an atom? How are they similar?
2 Guide the Learning
• Section 10.2 presents nuclear reaction equations using N to represent the
chemical symbol, Z to represent the mass number, and A to represent the
atomic number. To prepare students for this notation, introduce it here
while referencing Figure 4. Write the following on the board: AZN. Have
students identify which part of Figure 4 corresponds to each part of the
notation.
• Students might be tempted to think that, because the atomic number
represents the number of protons, the mass number must represent the
number of neutrons. Reiterate that the mass number is the sum of the
number of protons and the number of neutrons, and that the number of
neutrons can be found by subtracting the atomic number from the mass
number:
number of neutrons Z A
Language Arts
Connection
Word roots, particularly
those from Greek and
Latin, are very important to
scientific terminology. Have
students look up the
meanings of the following
roots: pro-, deut-, tri-, and
iso-. Ask them how
knowing the meanings of
these roots can help them
remember terms from this
section.
• Sample Problem—Practice problem solution
The symbol for beryllium-9 is 49Be. From the periodic table, we know that
beryllium has 4 protons. Remember that the top number in the symbol is
the mass number, which is the sum of the number of protons and the
number of neutrons. Since 9 4 5, we know that there are 5 neutrons.
3 Consolidate and Extend
• Review with students the terminology discussed in the section (proton,
neutron, and isotope). Ask them to describe the relationship between each
term and nucleus, atomic number, and mass number.
• Students might begin to confuse terminology presented in this section
with previously learned terms such as ion. Remind students that ions are
atoms with positive or negative charges. Ions of an element have the same
number of protons and may have the same number of neutrons. Point out
that every atom is an isotope of some element. Thus, every ion is also an
isotope. The opposite statement, however, is not necessarily true. An
isotope (atom) is not necessarily an ion.
• Have students complete the Check Your Understanding questions.
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Unit C: Radioactivity
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CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. In Thompson’s raisin bun model, the raisins represent negatively charged particles (electrons), and the bun
represents positively charged matter.
2. Thompson’s assumption was reasonable because equal amounts of positive and negative charge would make
the atom neutral overall. This in turn supported the idea that matter as a whole is basically neutral.
3. The diagram shows that many positively charged particles were able to pass through the thin sheet of gold
with little or no deflection. A large nucleus would increase the chance that incoming particles would come
near the nucleus or strike it. Very few particles were deflected, however, indicating that few actually came
near or struck the nucleus. This suggested that the nucleus was very small. Because like charges repel one
another, the deflection backward of positively charged particles indicated that the nucleus has an overall
positive charge.
4. In the planetary model of the atom, the Sun represents the nucleus, and the planets represent electrons.
According to this model, the force holding the atom together is the electric force between the positively
charged nucleus and the negatively charged electrons.
5. A proton is a single particle with a positive charge. A hydrogen atom contains both a proton (its nucleus) and
an electron.
6. 1.83 103 electrons
7. The neutron was difficult to detect because it is neutral.
8. Unlike a proton or an electron, a neutron has no electric charge.
9. The atomic number indicates the number of protons in the nucleus. The mass number of an atom is the sum
of the number of protons and the number of neutrons.
10. Answers may vary. Sample answer: Isotopes are atoms of the same element that have different numbers of
neutrons.
11. Diagram should have a nucleus made up of 8 protons and 10 neutrons and should have 8 electrons around the
nucleus.
12. The nucleus of an atom of chlorine-35 has 18 neutrons. The nucleus of an atom of chlorine-37 has 20
neutrons.
13. Table 2 Isotopes of Elements
Isotope name
astatine-211
uranium-235
magnesium-25
radon-209
chlorine-37
deuterium
silicon-30
palladium-102
iodine-127
tantalum-180
tungsten-182
Symbol
211
85 As
235
92 U
25
12 Mg
209
86 Rn
37
17 Cl
2
1H
30
14 Si
102
46 Pd
127
53 I
180
73 Ta
182
74 W
Number of protons
Number of neutrons
85
126
92
143
12
13
86
123
17
20
1
1
14
16
46
56
53
74
73
107
74
108
14. All isotopes of the same element have the same number of protons. For a neutral atom, the number of
protons equals the number of electrons. Because the electrons determine an atom’s chemical properties, the
chemical properties of an atom of a given element are the same regardless of the number of neutrons.
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Chapter 10 Radioactivity and the Atom
9
Reading and
Thinking Strategies
Analyze Tables
• Students can practice analyzing isotope symbols. Have students work with partners to analyze the material
in the table. Encourage students to cover the Comment column in the text and write their own comments
describing what they can tell about each isotope from its symbol. Then have students share with their
partner what they wrote and correct together any misconceptions they had. Students should be able to
explain how the isotopes in the table are the same and how they are different.
Meeting Individual Needs
ESL
• Have students complete a 3-column table with column headers Particle, Charge, and Where found (i.e.,
nucleus or outside nucleus) for quick reference.
Extra Support
• Provide support for students as they analyze the chemical symbol, mass number, and atomic number for an
atom. Re-create the symbol on page 281 on the board as 6 6 126C. Use one colour of pen or chalk to circle
the bottom “6.” Ask students what the number represents. Draw a line connecting this circled “6” to the
first “6” in the equation, and circle that number in the same colour. Then ask students what the other “6”
in the equation represents. Circle that “6” in a different colour. Then put a box around the “12” in a third
colour. Label it “mass number.” Present students with several other examples and have them work through
interpreting each symbol in this same manner.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Evidence that students can
• describe what Rutherford’s gold foil experiment revealed about the structure of an atom
• identify the differences between protons, neutrons, and electrons
• describe the difference between atomic number and mass number
• explain what isotopes are and write symbols for isotopes
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Unit C: Radioactivity
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10.3 Radioactive Decay
Page 284
PRESCRIBED LEARNING OUTCOMES
Time
• explain radioactivity using modern atomic theory
90–120 min
KNOWLEDGE
Key Ideas
• radioactivity
• conservation of mass
SKILLS AND ATTITUDES
• write and balance nuclear equations
• use the periodic table and ion charts
• use appropriate types of graphic models and/or formulas to represent a given
type of data, including the Bohr model
ICT OUTCOMES
• demonstrate competence in using basic information technology tools
There are three basic types
of radioactive decay and
these processes can be
written as nuclear reaction
equations.
Vocabulary
•
•
•
•
•
•
radioactive decay
parent nucleus
daughter nucleus
alpha particle
beta particle
gamma ray
Program Resources
SCIENCE BACKGROUND
Types of Radioactivity
• The alpha, beta, and gamma decay
discussed in the Student Book are
not the only types of radioactive
decay. Positron decay and electron
capture are two additional types of
radioactive decay.
• Positron decay is actually another
mode of beta decay. The beta decay
discussed in the Student Book (
decay) involves emission of a
negatively charged electron that is
created in the nucleus. In positron
decay ( decay), the nucleus emits
a positron, or a positively charged
0
electron ( 1
e). In general, isotopes
that undergo decay have too
many neutrons relative to number of
protons to be stable. Isotopes that
undergo decay typically have too
many protons relative to the number
of neutrons to be stable.
• In electron capture (EC), the nucleus
absorbs an orbital electron. Electron
capture is sometimes referred to as
K-capture. K refers to the innermost
electron shell from which a nucleus
would typically capture an electron.
An electron from a distant orbit,
however, can also be captured by
the nucleus.
Related Resources
Wilson, Jerry D., and
Anthony Buffa. College
Physics, 5th Ed. NJ:
Prentice-Hall, Inc., 2002.
B.C. Probe 10
Computerized
Assessment Bank
TEACHING NOTES
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
1 Getting Started
• Teacher Demo: Modeling Penetrating Abilities
– Guide students to consider the effect of particle (or wavelength) size on
ability to penetrate different materials. If you have the following
materials available, use them to demonstrate. Otherwise, show images or
ask students to visualize the materials: Group A—a piece of window
screen, plastic wrap, and a piece of construction paper; Group B—
popcorn kernels, sand or salt, and light. The mesh on the window screen
should be large enough to allow sand and salt crystals to pass through.
– Ask students to predict which materials in Group B will be able to
penetrate each material in Group A.
NEL
WS 10.3-1 Study Guide
WS 10.3-2 Radioactive Decay
BLM 10.3-1 Alpha, Beta, and
Gamma Decay
BLM 10.3-2 Writing Nuclear
Equations
Nelson Science Probe 10
Website
www.science.nelson.com
Thomson Gale Science
Resource Center
Nelson Science Probe 10
Website
www.science.nelson.com
Animations
– A Geiger Counter
– Half-life and
Radiochemial Dating
Chapter 10 Radioactivity and the Atom
11
– With student volunteers assisting as necessary, alternately try to pour (or
focus) each material in Group B through each material in Group A. Ask
students what they can conclude about particle (or wavelength) size and
ability to penetrate materials. Remind students of this exercise as they
consider the penetrating ability of different kinds of radiation.
• Possible Misconceptions
– Identify: Students might mistake nuclear decay equations for chemical
equations.
– Clarify: Nuclear reactions generally involve an atom’s nucleus (i.e., its
protons and neutrons). Chemical reactions involve only an atom’s
electrons. Therefore, nuclear equations generally show the atomic
numbers and mass numbers of the atoms involved. Chemical equations
generally do not show atomic numbers or mass numbers.
– Ask What They Think Now: Ask, How is a nuclear reaction different from a
chemical reaction?
2 Guide the Learning
• Introduce and explain each type of radioactive decay. Use the general
equation and the sample problem to illustrate the reaction. You can use
BLM 10.3-1 Alpha, Beta, and Gamma Decay as an overhead to refer to as
you describe each type of decay.
• Have students perform Investigation 10A: Penetrating Ability of Nuclear
Radiation. (See teaching notes for Investigation 10A on page 15.)
Connections: Personal
Planning
Spending your career
studying radioactive
isotopes might not seem
glamorous at first, but
physicists who specialize in
nuclear medicine might
disagree. These scientists
save lives with their
knowledge of radioactivity
and radioactive decay.
• Sample Problem 1—Practice problem solution
We can find the symbol and atomic number for radium on the Periodic
Table (Ra; 88). When an atom undergoes alpha decay, the products are a
daughter nucleus and an alpha particle, 42He. The total charge and total
numbers of protons and neutrons must be equal on both sides of the
equation.
226
88
Ra
៮៬
222
86
Rn 42He
Radium has been transmuted into radon.
• Sample Problem 2—Practice problem solution
We can find the symbol and atomic number for xenon on the periodic
table (Xe; 54). When an atom undergoes beta decay, the products are a
daughter nucleus and a beta particle.
133
54
Xe
៮៬
133
55
Cs 01e
Xenon has been transmuted to cesium.
• Sample Problem 3—Practice problem solution
We can find the symbol and atomic number for cobalt on the periodic
table (Co; 27). When an atom undergoes gamma decay, the product is an
atom in the ground state and a gamma ray.
៮៬ 2860Ni* 0 1e
60
28Ni*
៮៬ 28Ni 0
60
27
Co
60
0
Cobalt has been transmuted to Nickel.
12
Unit C: Radioactivity
NEL
3 Consolidate and Extend
• For students who need extra practice working methodically through
nuclear equations, you can use as a handout BLM 10.3-2 Writing Nuclear
Equations.
• Have students complete the Check Your Understanding questions.
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. When a radioactive atom undergoes radioactive decay, its nucleus emits radiation (alpha particles, beta
particles, and/or gamma rays).
2. It would take 7 000 beta particles to equal the mass of one alpha particle.
3. Gamma rays are not particles because they do not have mass. They are waves of electromagnetic radiation.
When a nucleus emits gamma rays, its mass does not change; it only loses energy.
4. Sample response: In transmutation, an atom changes from one element to another.
5. During alpha decay, the atomic number (Z ) decreases by 2 and mass number (A) decreases by 4.
6. A helium atom has electrons, but an alpha particle does not. A helium atom is stable, but an alpha particle is
not.
7. (a)
(b)
(c)
180
72 W
147
62Sm
20
11Na
176
4
70 Hf 2He
៮៬ 143
4
៮៬16 60Nd4 2He
៮៬ 9F 2He
8. Sample response: In beta decay, the nucleus emits an electron (a beta particle).
9. The electron came from the decay of a neutron into a proton, an electron, and a neutrino. Because the
nucleus gains a proton, it becomes a different element.
10. (a)
(b)
(c)
64
28 Ni
3
1H
59
26 Fe
64
0
៮៬3 29Cu 01e
1e
៮៬ 2He
59
0
៮៬ 27Co 1e
11. Atomic number and mass number do not change as a result of gamma decay. An atom emits gamma
radiation to return to a ground state from an excited (high energy) state.
12.
60
26Fe
60
27Co*
60
0
៮៬ 2760Co 10e
៮៬ 27Co 0
13. (a) beta
(e) alpha
14. (a)
(d)
(g)
239
94Pu
0
0
0
1e
(b) alpha
(f) gamma
(b)
(e)
(h)
228
88Ra
4
2He
239
93Np
(c) alpha and beta
(d) gamma
(g) alpha
(h) alpha, beta, and gamma
(c)
(f)
(i)
0
1e
213
83Bi
99
43Tc*
15. In a cloud chamber, a radioactive source emits charged particles that cause the gas in the chamber to
become ionized. The ions cause vapor to condense and leave visible tracks. In a bubble chamber, a charged
particle passes through a superheated liquid, leaving tracks that show the direction of deflection of the
particle. A Geiger counter registers bursts of electric current created by radiation.
16. Gamma rays are not charged particles, so they cannot produce ions inside a gas chamber (which leads to the
formation of tracks).
17. Alpha particles leave larger tracks than beta particles because they produce a great deal of ionization over a
shorter distance.
18. Both Geiger counters and cloud chambers detect radiation by utilizing the ability of some forms of radiation
to ionize atoms.
19. Some Geiger counters cannot detect alpha radiation because alpha particles cannot penetrate the window at
the end of the cylinder.
NEL
Chapter 10 Radioactivity and the Atom
13
Reading and
Thinking Strategies
Adjusting Reading Pace
• Remind students that adjusting their reading rate for sections of difficult text can help with understanding.
Have students work with partners to identify areas of text they found difficult. Then have students reread
these sections more slowly. Students should then summarize and explain these sections to their partners.
Strategies for Success
Summarizing
• Have students write brief summaries for each type of radioactive decay. Use BLM 10.3-1 Alpha, Beta, and
Gamma Decay as an overhead that students can referece as they write their summaries.
Meeting Individual Needs
Extra Support
• Encourage students to make flash cards for the three main types of radioactive decay (e.g., a card with
“alpha particle” on one side and “a helium nucleus, 42He” on the other side) and for characteristics such as
“does not change mass number or atomic number (gamma decay)” and “emits a negatively charged particle
(beta decay).” Students can work in pairs to find relevant characteristics from the text to use for their flash
cards.
Extra Challenge
• Introduce these students to an additional decay process: positron emission.
A positron is a positively charged particle represented by the symbol 10. Challenge students to write the
equations for the positron emission of polonium-207:
207
207
0
84Po
៮៬ 83Bi 1
Have students explain how the result of positron emission differs from that of beta decay. (The atomic
number decreases by one following positron emission and increases by one in beta decay.)
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Evidence that students can
• define alpha particle, beta particle, and gamma ray
• determine whether a nuclear equation represents alpha, beta, or gamma decay
• write nuclear equations for alpha, beta, and gamma decay
• identify materials that can stop the penetration of alpha particles, beta particles, and gamma rays
• explain why mass number and atomic number do not change during gamma decay
14
Unit C: Radioactivity
NEL
10A Investigation: Penetrating Ability
of Nuclear Radiation
PRESCRIBED LEARNING OUTCOMES
•
•
•
•
explain radioactivity using modern atomic theory
perform experiments using the scientific method
demonstrate safe procedures
demonstrate competence in the use of technologies specific to investigative
procedures and research
• demonstrate scientific literacy
Page 298
Time
30–45 min
Key Ideas
The atoms of some elements
are radioactive, which means
that they undergo radioactive
decay.
• radioactivity
• elements of a valid experiment
There are three basic types
of radioactive decay and
these processes can be
written as nuclear equations.
SKILLS AND ATTITUDES
Skills and Processes
• recognize dangers
• use the Internet as a research tool
Conducting
Recording
Analyzing
Evaluating
Synthesizing
Communicating
KNOWLEDGE
SCIENCE BACKGROUND
Ionization
• An ion is an atom with a positive or
negative charge. Ions with opposite
charges attract each other.
• When a charged particle, such as an
alpha or beta particle, enters the gasfilled tube of the Geiger counter, the
particle ionizes gas atoms. In
ionization, a particle removes an
electron from an atom, creating
an ion.
• In a Geiger counter, ions are
attracted to particles or areas of
opposite charge. The ions that form
in the gas-filled tube are attracted to
charged plates, creating an electric
current that produces the pulse or
“count.”
Detecting Radiation
• The activities of some industries
expose workers to high levels of
radiation. Workers in these industries
typically wear dosimeters, devices
that monitor radiation exposure. The
simplest dosimeters are film badges.
Upon exposure to radiation, the film
darkens. The degree of darkening
indicates the level of exposure.
• A rad is a unit used to express the
amount of radiation absorbed by a
NEL
certain quantity of material. A rem is
the unit used to express the effects
of radiation on living things.
Electromagnetic Spectrum
• Unlike alpha and beta radiation,
gamma rays are not particles.
Gamma rays are electromagnetic
radiation, which is a form of energy.
Electromagnetic radiation travels in
waves and can be described in
terms of wavelength, or the distance
between two consecutive wave
peaks. The electromagnetic
spectrum includes all the
wavelengths of electromagnetic
radiation.
• The visible part of the spectrum
includes those wavelengths of
electromagnetic radiation (“light”)
that humans can detect.
• Gamma rays are high energy rays
with very short wavelengths. X-rays
have longer wavelengths than
gamma rays, but both types of rays
are beyond the visible part of the
spectrum.
Lesson Materials
For teacher demo
• set of radioactive samples
(alpha, beta, and gamma
sources)
• Geiger counter
• 10 sheets of paper
• 10 sheets of aluminum foil
• 10 lead sheets
Program Resources
BLM 10.3-1 Alpha, Beta, and
Gamma Decay
Investigation BLM 10A
Penetrating Ability of Nuclear
Radiation
Rubric 18: Conduct an
Investigation
Rubric 19: Conduct an
Investigation—
Self-Assessment
SSP Rubrics 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, & 20
Nelson Science Probe 10
Website
www.science.nelson.com
• Visit the Nelson Science Probe 10
website for links to more information
about the electromagnetic spectrum.
Chapter 10 Radioactivity and the Atom
15
INVESTIGATION NOTES
Student Safety
• The radioactive sources used are very weak. However, care needs to be
taken around any radioactive sources. Do not come any closer to them
than needed, and keep them in storage until needed.
• Do not allow students to handle the radioactive sources. Do not allow
the radioactive source to come into contact with bare skin.
Related Resources
B.C. Probe 10
Computerized
Assessment Bank
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
Thomson Gale Science
Resource Center
Nelson Science Probe 10
Website
www.science.nelson.com
• Review the section on Radiation Hazards in the BC Science Safety
Resource Manual. A link to this document is available at:
www.science.nelson.com.
• Remind students not to allow watches anywhere near the Geiger counter.
Some watches (typically older watches) contain radioactive materials that
allow the watch faces to glow in the dark. The Geiger counter will detect the
radiation given off by such watches, producing a false reading.
Question
• Ask students how much of each type of material they think will be needed to
stop alpha, beta, and gamma radiation.
Experimental Design
History Connections
The harmful effects of
radiation have not always
been known. Once they
were recognized, however,
it became important to
learn how to prevent
radiation from affecting
people working with
radioactive materials. Have
students research the
history of radiation safety
protocols and procedures.
• During the investigation, be sure to hold the Geiger counter at the same
distance from the radioactive source for every reading. Point out to students
that you are doing this, and ask them why this is important. (During an
investigation, one should keep all conditions except one—here, type of
material—constant.)
Materials
• Some Geiger counters come equipped with a holder that has a place for the
radioactive source. If the Geiger counter you have available does not,
maintain consistency during the investigation by using two ring stands with
clamps to hold the radiation sources and the Geiger counter.
Procedure
• For Step 2, guide students to conclude that the acceptable “blocked”
radiation should be equal to the level of background radiation they
determined in Step 1. Ask students why they are unable to block
background radiation in this instance. (The Geiger counter is detecting
radiation from all sides of the “blocking” material.)
Analysis
(a) The
decay rate seemed to decrease. The radiation travels outward from the
source in all directions. The farther from the source the Geiger counter is,
the less radiation will strike its detector.
(b) Although
everyone was exposed to some radiation, the teacher was probably
exposed to more because he or she was handling the radioactive sources.
(c) alpha
16
Unit C: Radioactivity
particles, beta particles, gamma rays
NEL
Evaluation
(d) Sample
answer: The Geiger counter “counted” even when no sources were
nearby. We took this to be background radiation and used the average
number of clicks as a control. We subtracted this average number of clicks
from the counts we recorded for each source. We considered a type of
radiation to be blocked when no more counts were registered than for the
control (no source nearby).
(e) Sample
answer: The tube should be placed in the holder instead of the
teacher’s hand so that the teacher’s hand does not interfere with the reading.
Synthesis
(f)
Background radiation could account for counts when none of the sources
was nearby.
(g) X-rays
are more penetrating than alpha and beta particles but less
penetrating than gamma rays.
(h) Sample
answer: If I worked in a hospital that used radioactive sources,
I would try to protect myself with lead-lined protective clothing, because
enough lead will stop alpha, beta, and gamma radiation.
Meeting Individual Needs
ESL
• Be sure students understand the meaning of penetrate before they begin the investigation. Tell students that
penetrate means “move into” or “move through.” For beginning ESL students, reinforce the meaning by
pouring water through a thin piece of cloth while nodding your head and saying The water penetrates. Pour
popcorn kernels or other small objects onto the cloth while shaking your head and saying The popcorn does
not penetrate.
Extra Support
• Remind students of the demonstration carried out at the beginning of Section 10.3. Before students begin
their analyses of the investigation, have them work with partners to create analogies by matching the
materials and types of radiation used in this investigation to the materials (screen, plastic wrap, paper,
popcorn kernels, sand, light) used in the demonstration.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Evidence that students can
• describe the relative penetrating abilities of alpha, beta, and gamma radiation
• explain the importance of controls in investigations
NEL
Chapter 10 Radioactivity and the Atom
17
10.4 Half-Life
Time
90–120 min
Key Ideas
The rate of decay of a
radioactive sample is
predictable and is described
by the half-life of the
radioactive isotope.
Vocabulary
• half-life
• decay series
Program Resources
BLM 10.4-1 Radioactive
Decay and Half-Life
WS 10.4-1 Study Guide
WS 10.4-2 Half-Life
WS 10.4-3 Half-Life
Calculations
WS 10.4-4 TechConnect:
Brachytherapy
Nelson Science Probe 10
Website
www.science.nelson.com
Related Resources
B.C. Probe 10
Computerized
Assessment Bank
Page 290
PRESCRIBED LEARNING OUTCOMES
• explain radioactivity using modern atomic theory
• demonstrate scientific literacy
• represent and interpret information in graphic form
KNOWLEDGE
• radioactivity
SKILLS AND ATTITUDES
• use the periodic table and ion charts
• use line graphs to extract and convey information
• deduce relationships between variables given a graph or by constructing
graphs
ICT OUTCOMES
• demonstrate the ability to formulate questions and to use a variety of sources
and tools to access, capture, and store information
SCIENCE BACKGROUND
Calculating Half-Life and Decay
Equations
• The number of parent nuclei in a
sample decays exponentially over
time. At any time t, one can
calculate the number of parent nuclei
remaining in a sample (P ) using the
equation P Poe–t, where is a
constant that is unique to the
particular parent isotope and Po is
the number of parent nuclei initially
present in the sample. The decay
constant is equal to the natural
logarithm of two (ln 2) divided by the
half-life of the isotope.
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
Thomson Gale Science
Resource Center
Nelson Science Probe 10
Website
www.science.nelson.com
18
Unit C: Radioactivity
• Because each parent nucleus decays
to form a daughter nucleus, the
number of parent nuclei is inversely
proportional to the number of
daughter nuclei in a sample, once
the number of initial daughter nuclei
in the sample is accounted for. One
can calculate the number of
daughter nuclei present (D ) at time t
using the equation D Do P
(et 1), where Do is the number of
daughter nuclei initially present in
the sample. If there were no
daughter nuclei initially present and if
no parent or daughter nuclei are lost
during decay, then D P Po at
any time t.
TEACHING NOTES
1 Getting Started
• Teacher Demo: Modeling Half-Life
– Have all of the students in the class stand in a line. The students should
all be facing the same direction. (If there is an odd number of students
in your class, stand in line with the students so that there is an even
number of people in line.) Explain that, every minute, one-half of the
people in line will sit down. Ask students to predict how many minutes
it will take for three-quarters of the people in line to be sitting down.
(You may wish to convert the fraction into an actual number. For
NEL
example, if your class contains 24 students, you would ask how many
minutes it will take for 18 of the students to be sitting down.)
– Once students have made their predictions, carry out the demonstration.
Have the class time one minute, and then choose half the students at
random to sit down. After another minute, choose half of the remaining
students at random to sit down. At this point, one-quarter of the
original number of students should be standing. If your class is large
enough, continue for one more minute.
– Have the remaining students return to their seats, and explain to the
entire class that they just modeled the behaviour of a radioactive
substance with a half-life of 1 minute. Ask students to volunteer what
they know about the term half-life. Explain that the half-life of a
radioactive substance is the time required for one half of the radioactive
atoms present to decay
Math Connections
Radioactive decay follows
an exponential curve
(a curve with the equation
y ex). Have students
make graphs of
exponential functions and
compare them to the
decay curves shown in
this section. Have
students research other
reactions and processes
that follow exponential
curves.
• Possible Misconceptions
– Identify: Carbon dating can be used to study all things that were alive in
the past. Students may apply knowledge of carbon dating to situations in
which it would be impossible to carbon date, such as when studying
ancient life such as dinosaurs.
– Clarify: Carbon-14 has a relatively short half-life. Although students may
have heard of carbon dating, they may not understand that carbon-14
can only be used to accurately date organic materials that are younger
than 60 000 years.
– Ask What They Think Now: Ask students if it would be appropriate to
carbon date the remains of an organism that lived 150 000 years ago.
They should recognize that carbon dating would not be an effective
dating method for that particular organism.
2 Guide the Learning
• You can use BLM 10.4-1 Radioactive Decay and Half-Life as an overhead to
illustrate half-life.
• Sample Problem 1––Practice problem solution
(a) First, determine how any half-lives have passed. The fraction left is
12.5 mg
50 mg
1
4
1
22
We can see that 2 half-lives have passed. Now, calculate the total
amount of time that has passed: 2 1.8 h 3.6 h
From the graph, we can see that at about 3.6 hours, the mass is
reduced to 12.5 mg.
(b)
Since the half-life of fluorine-18 is 1.8 h, we can determine the
number of half-lives:
5.4 h
1.8 h
3 half-lives
Now calculate the mss remaining.
1
m 冢 23 冣 (50 mg) 冢
1
8
冣 (50 mg) 6.25 mg
The mass remaining is 6.25 mg. We can also see on the graph that the
approximate mass remaining after 2 half-lives is about 6 mg.
• Sample Problem 2—Practice problem solution
(a) First, determine the number of half-lives represented by 320 years.
NEL
Chapter 10 Radioactivity and the Atom
19
One half-life is 160 years, so 320 years is 2 half-lives. Then, calculate
the activity level of the sample after two half-lives.
1
a 冢 22 冣 (80 MBq) 冢
1
4
冣 (80 MBq) 20 MBq
The activity of the sample after 320 years will be 20 MBq.
(b) First, determine how many half-lives have passed since the activity of
the sample was 640 MBq.
640
80
8 23
So, three half-lives have passed since the activity was 640 MBq. Three halflives is equal to 3 160 years 480 years. The activity level of the
sample was 640 MBq 480 years ago.
• Sample Problem 3—Practice problem solution
From the graph, we can see that 25 % of the original carbon-14 remained
after about 11 000 to 12 000 years.
The decrease from 100 % to 25 % is a ratio of
Therefore, the time it takes is 5730
years
half–life
25 %
100 %
1
4
1
22
2 half-lives 11 460 years.
The bone fragment is about 11 000 years old.
• Use WS 10.4-3: Half-Life Calculations to check student learning.
• Have students perform Investigation 10B: The Half-Life of Popcorn to
apply what they have learned about rate of decay. (See teaching notes for
Investigation 10B on page 22.)
3 Consolidate and Extend
• Students have now had a chance to study radioactive decay and how this
phenomenon can be used by scientists to learn more about Earth’s past.
Have students reflect on how scientific discoveries lead to new
technologies, and that these new technologies in turn lead to more new
scientific discoveries.
• Have students complete the Check Your Understanding questions.
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. Activity (the number of decays per second) is measured in becquerels. One Bq equals one decay per second.
2. (a) 86 Bq
(b) 1.7 102 Bq
3. (a) about 160 000 atoms
(c) 1.0 102 Bq
(d) 1.1 101 Bq
(e) 75 Bq
(b) about 400 000 atoms
(c) about 10 minutes
(d) about 30 000 atoms
(b) 14 Bq
(c) about 106 days (2 half-lives)
4. 1.9 g
5. (a) 448 Bq
(d) 1792 Bq
(e) 159 days
6. Carbon-14 has a relatively short half-life. After a few half-lives (a few tens of thousand of years), only tiny
amounts of C-14 would remain. In addition, carbon-14 dating is used to date materials from sources that
were once living. Granite was never alive, so carbon-14 cannot be used to date a granite rock.
7. about 4 000 years
8. about 11 000 years (11 460 years)
9. about 3 % (3.125 %)
20
Unit C: Radioactivity
NEL
Reading and
Thinking Strategies
Reading Graphs
• Have students examine Figure 5 and describe the trend shown in the graph. Ask them to predict what the
curve might look like if it extended to 6 minutes. Students should be able to predict that the line will
continue to curve downward, but it will become less steep as time passes.
Meeting Individual Needs
ESL
• To visually indicate the meaning of half-lives, give ESL students a series of tiles or squares of paper, and
have them illustrate half-life by moving half, then half again, then half again, (each in a specific period of
time). Then, have students repeat the activity, labeling the stable isotope tiles as they work through each
half-life.
Extra Support
• Remind students as they work through the problems that the type of radioactive compound in each
problem does not change the underlying mathematical formulas they should apply. Each compound has its
own half-life, but half-life itself is always a standard percentage or fraction of the total.
TechCONNECT: Brachytherapy
PAGE 297
• Radiation treatments themselves are not painful, although the side effects of radiation therapy can be
difficult to manage for some patients. After treatment, patients may worry that they themselves are
radioactive. After brachytherapy, some radiation may temporarily be passed through urine or saliva, but the
amounts passed are small and generally not harmful to healthy adults.
• Brachytherapy kills cancer cells by destroying the cells’ genetic material, DNA. The energy given off by
radioactive isotopes damages the DNA of cancer cells, making them unable to grow and divide. In fact,
radiation therapy affects all types of body cells, not just cancer cells. However, most normal body cells are
able to withstand the effects and repair themselves. Cancer cells are affected much more profoundly.
Brachytherapy is a particularly effective cancer therapy because it targets cancer cells while minimizing the
amount of genetic damage done to healthy body cells.
• Scientists and medical researchers are looking for other ways to use brachytherapy. There is some promising
evidence that brachytherapy may be helpful in treating abnormal narrowing of the arteries after angioplasty.
• Have students complete WS 10.4-4 TechConnect: Brachytherapy.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Evidence that students can
• define the term half-life
• use given information related to a sample’s half-life and amount of parent and daughter isotopes to determine the age of a sample
• use given information related to the age of a sample to determine the ratio of parent to daughter isotopes
NEL
Chapter 10 Radioactivity and the Atom
21
10B
Investigation: The Half-Life of Popcorn
Time
45–60 min
Key Ideas
The rate of decay of a
radioactive sample is
predictable and is described
by the half-life of the
radioactive isotope.
Skills and Processes
Predicting
Conducting
Recording
Analyzing
Evaluating
Synthesizing
Communicating
Lesson Materials
per group
• 100 popcorn kernels
• container such as an empty
film canister or a Petri dish
Program Resources
BLM 10.4-1 Radioactive
Decay and Half-Life
Investigation BLM 10B The
Half-Life of Popcorn
Rubric 18: Conduct an
Investigation
Rubric 19: Conduct an
Investigation–
Self-Assessment
SSP Rubrics 5, 6, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19,
& 20
Nelson Science Probe 10
Website
www.science.nelson.com
Page 300
PRESCRIBED LEARNING OUTCOMES
• explain radioactivity using modern atomic theory
• perform experiments using the scientific method
• represent and interpret information in graphic form
KNOWLEDGE
• radioactivity
• elements of a valid experiment
SKILLS AND ATTITUDES
• communicate results
• use bar graphs, line graphs, pie charts, tables, and diagrams to extract and
convey information
• deduce relationships between variables given a graph or by constructing
graphs
SCIENCE BACKGROUND
Radioactive Decay
• The decay of a specific radioactive
nucleus cannot be predicted.
However, when large numbers of
nuclei are present, the overall decay
of the sample can be predicted
statistically.
• The half-life of an isotope is the time
required for one half of the parent
nuclei present to decay to daughter
nuclei. Note that half-life cannot be
used for single nuclei. It applies only
to large numbers of nuclei.
• Although the half-life of a particular
isotope is a constant, the rate of
decay of a sample is not. This is
because the rate of decay is an
absolute number, but the half-life is a
relative number. The rate of decay is
defined as the number of decays per
minute or per second. It is a function
of how many parent nuclei are left.
When there are many nuclei left,
there will be many decays per
second. When few nuclei are left,
the decay rate will be lower. The
half-life is constant, however,
because the time required for the
number of nuclei to decrease by half
is fixed.
INVESTIGATION NOTES
Related Resources
B.C. Probe 10
Computerized
Assessment Bank
B.C. Science Probe 10
Create and Present:
Modifiable Presentations
and Illustrations CD
Thomson Gale Science
Resource Center
Student Safety
• Clean-up following the activity should involve sweeping the floor.
Kernels could be a slipping hazard.
• Make sure students do not eat unpopped kernels. They could be a
choking hazard. To discourage students from eating the raw popcorn,
remind them that the kernels have been handled by other students and
have probably been on the floor.
Nelson Science Probe 10
Website
www.science.nelson.com
22
Unit C: Radioactivity
NEL
Question
• Note that the rate of radioactive decay is a function of the number of parent
nuclei present. However, unlike the “decay” modeled in this activity,
radioactive decay follows a constant half-life curve.
Prediction
• Sample answer: The rate of decay will decrease when there are fewer parent
nuclei left.
Materials
• If popcorn is unavailable, you may substitute coins, M&Ms, dice, or any
other objects with distinctive sides. If this substitution is made, you should
tell students what state corresponds to decay (e.g., for M&Ms, the side with
the M could be undecayed and the side without the M could be decayed).
• You may wish to count out the popcorn kernels for each group ahead of
time and then store kernels in small containers such as 35 mm film canisters
for future use.
Procedure
• Some kernels will land such that their “points” face straight up in the air.
You may instruct students to count these kernels as decayed or undecayed as
you see fit.
• Make sure students separate the parent and daughter kernels after each
shake.
Analysis
(a) Over
(b) The
time, the number of parent kernels decreased.
Social Studies
Connections
Nuclear power plants
produce radioactive waste
with a fairly long half-life.
The long half-life
complicates decisions
about where to store the
waste. Have students
research some of the
proposed storage
solutions for radioactive
waste and discuss the
pros and cons of each
solution.
rate at which daughter kernels were produced decreased with time.
(c) Sample
answer: It took 11 shakes for all the parent kernels to decay. This is
about the same as the rest of the groups.
answer: Based on the graph, it took about 1.8 shakes to reduce the
number of parent kernels to about 50. It took about 3.6 shakes to reduce
the number of parent kernels to about 25.
Number of Parent Kernels Remaining
(d) Sample
100 •
90
80
70
60
50
40
30
20
10
0
0
(e) Sample
NEL
Number of Parent Kernels vs. Time
♦
♦
♦
♦
1
2
3
4
♦
5
♦
♦
♦
♦
6
7
8
9
♦
10
•
11
Time (shakes)
answer: The half-life of the popcorn is about 1.8 shakes.
Chapter 10 Radioactivity and the Atom
23
Evaluation
(f)
The popcorn was similar to parent nuclei because its “decay rate” depended
on the number of parent kernels remaining. It is different because popcorn
kernels are not radioactive, they are much larger than radioactive nuclei,
and the definition of decay in the investigation is arbitrary.
Synthesis
(g) Sample
answer: No, my results are not exactly the same as my classmates’.
This is probably because the orientation of the popcorn kernels is random.
(h) Sample
answer: If this experiment had been performed with 10 000 kernels
of popcorn, the results from different students would probably have been
more similar.
(i)
Sample answer: Because the criteria for “decaying” would be narrower, fewer
kernels would qualify each round. If kernels take longer to decay, the halflife will be longer.
(j)
Sample answer: If we used a computer to generate random numbers, we
could assign a certain range of numbers to represent decayed nuclei, and
record how many decayed nuclei were produced at each iteration. Each
iteration would also have to contain a smaller number of random numbers
than the previous iteration. The number of undecayed numbers in the
previous iteration would determine the number of numbers generated in
the next iteration.
Meeting Individual Needs
ESL
• Allow beginning ESL students to respond to Conclusion questions by drawing simple pictures to
accompany or to replace text.
Extra Support
• To support the students in writing their conclusions, encourage them to use graphic organizers to organize
the information before composing responses. For example, have students create a Venn diagram for the
Evaluation question.
• Use BLM 10.4-1 Radioactive Decay and Half-Life as an overhead for students to refer to complete their
analyses.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Evidence that students can
• explain half-life in terms of rates of radioactive decay
• use half-life graphs to determine the half-lives of substances and to determine how many parent nuclei and daughter nuclei were
present in a sample after a given amount of time
• define concepts operationally in the design and analysis of their radioactive decay models
• create graphs with appropriate scale and axes
24
Unit C: Radioactivity
NEL
CHAPTER
10
Review
Page 302
Time
Chapter 10 Review Chart
45–60 min
• Have students complete WS 10.0-1 Matching Challenge: Radioactivity to
review the chapter vocabulary.
Skills and Processes
The Chapter Review provides
an opportunity for students to
demonstrate their
understanding of and their
ability to apply the key ideas,
vocabulary, and skills and
processes.
Program Resources
BLM 10.0-1 Radioactivity
Concept Map
WS 10.0-1 Matching
Challenge: Radioactivity
WS 10.0-X Chapter Key Ideas
Chapter 10 Quiz
Nelson Science Probe 10
Website
www.science.nelson.com
• For extra support, have students use the vocabulary list for the chapter to
complete BLM 10.0-1 Radioactivity Concept Map showing how all the
vocabulary terms are related.
• Have students review their Study Guides to recall what they have learned in
this chapter.
• Have students complete the Chapter 10 Quiz to review the vocabulary and
concepts in this chapter.
• Encourage students to visit the online quiz centre on the Nelson Science
website and complete the Chapter 10 Self-Quiz.
• Have students use BLM 10.0-X Chapter Key Ideas to review the key ideas in
the chapter.
Review Key Ideas and Vocabulary—Suggested Answers
1.
Diagram should contain a nucleus with 6 protons and 8 neutrons. There
should be 6 electrons outside the nucleus. Added together, the number of
protons and the number of neutrons equals the mass number. The number
of electrons and the number of protons are equal.
2.
Isotopes are atoms of the same element that have different masses due to different numbers of neutrons
in their nuclei.
3.
A
4.
During alpha decay, the nucleus emits a helium nucleus, decreasing its atomic number by 2 and its
atomic mass by 4. During beta decay, the nucleus emits a beta particle (an electron), adding a proton to
the nucleus and thereby increasing its atomic number by 1.
5.
C
6.
D
Use What You’ve Learned—Suggested Answers
7.
One molecule of heavy water is two atomic mass units heavier than one molecule of normal water. (This
could also be described as a ratio:
16 2 2
16 1 1
1.11. Therefore, heavy water is 1.11 times greater in mass
than normal water.)
8.
NEL
232
90Th
228
88Ra
228
89Ac
228
90Th
224
88Ra
228
4
88Ra 2He
៮៬ 228
0
៮៬ 22889Ac 10 e
90Th 1e
៮៬ 224
4
88Ra 2He
៮៬ 220
4
៮៬ 86Rn 2He
1.4 1010 year
5.8 year
6.1 h
1.9 year
3.6 d
Chapter 10 Radioactivity and the Atom
25
220
88Rn
216
84Po
212
82Pb
212
83Bi
212
84Po
216
4
៮៬ 21284Po 42He
82Pb 2He
៮៬ 212
0
៮៬21283Bi 10e
84Po 1e
៮៬ 208
4
៮៬ 82Pb 2He
9.
0.16 s
10.6 h
60.5 min
0.3 s
C
10. (a)
11.
54 s
6
(b)
9.4 g
(c)
1600 Bq
(b)
about 7.5 days
(d)
13.5 days
B
12. (a)
47
20
Ca
៮៬ 21Sc 47
0
1
e
(c)
about 4.5 days
(e)
110 decays per second
13.
C
14.
C
Think Critically—Suggested Answers
15.
Radiation is emitted from an atom’s nucleus. Chemical changes involve electrons. Involving a radioactive
atom in a chemical reaction will not change the amount of radiation emitted.
16.
Possibilities for student research include: determining ages of rocks and fossils; determining ages of
organic materials, such as preserved human remains, cloth, and ancient “campfires”; using radioactive
elements as tracers in medical diagnoses; and using radiation in cancer therapies.
17.
Sample answer: Carbon-14 dating could not be used for dinosaur bones because the half-life of carbon-14
is far too short. To determine the age of dinosaur fossils, scientists can use radioactive dating to find the
age of the rock surrounding a fossil.
Reflect on Your Learning—Suggested Answers
18.
Sample answer: I know now that radiation does not just exist in science labs. There are many natural
sources of radiation. Radiation can be harmful, but there are some beneficial applications of radioactivity,
such as cancer treatments, dating many materials, and detecting smoke in homes.
Meeting Individual Needs
ESL
• Write the Key Ideas on the board or write them on sentence strips and post the strips on the wall. Write the
vocabulary terms on sentence strips or cards. Have students post the vocabulary words under the applicable
Key Idea. If students think a term belongs with more than one Key Idea, have them make additional
vocabulary cards and post them. Allow students to express whether or not they agree or disagree with the
placement of vocabulary terms. Once all vocabulary terms have been posted, have students explain how
each vocabulary term relates to the Key Idea. Allow beginning ESL students to express their ideas with
drawings or simple words and phrases.
Extra Support
• Have students work with partners to describe what concept each diagram or equation in the Key Ideas
Summary represents. Encourage them to cover the given notes as they try to come up with their explanations.
Have them identify the vocabulary words from the list on page 32 that apply to each diagram.
26
Unit C: Radioactivity
NEL
Chapter
10
Blackline Masters
Blackline Master 10.3-1
Name:
Date:
Alpha, Beta and Gamma Decay
ALPHA DECAY
BETA DECAY
GAMMA DECAY
Copyright © 2009 by Nelson Education Ltd.
Chapter 10 Blackline Master 10.3-1
29
Blackline Master 10.3-2
Name:
Date:
Writing Nuclear Equations
Complete or write the nuclear equations as indicated.
1. alpha decay of radon-217
What is the symbol for an alpha particle?
The atomic number of radon (Rn) is
The mass number of radon-217 is
Radon-217 has
, so radon has
.
neutrons.
During alpha decay, the number of protons
mass number
protons.
by
by
, and the
.
Write the complete equation for the alpha decay of radon-217:
42
Cl ៮៬ ? 10e.
2. 17
The atomic number of chlorine (Cl) is
The mass number of chlorine-42 is
and neutrons.
Chlorine-42 has
, so chlorine has
protons.
, so chlorine-42 has
total protons
neutrons.
During beta decay, the number of protons increases/decreases (circle one).
During beta decay, the number of neutrons
.
Write the complete equation for the beta decay of chlorine-42:
30
Chapter 10 Blackline Master 10.3-2
Copyright © 2009 by Nelson Education Ltd.
Blackline Master 10.3-2
Name:
Date:
Writing Nuclear Equations (continued)
3. beta decay of silver-106
The atomic number of silver (Ag) is
, so silver has
The mass number of silver-106 is
Silver-106 has
protons.
.
neutrons.
During beta decay, the number of protons
neutrons
by 1, and the number of
.
Write the complete equation for the beta decay of silver-106:
4. the gamma decay of titanium-44
The atomic number of titanium (Ti) is
protons.
, so titanium has
The mass number of titanium-44 is
Titanium-44 has
.
neutrons.
What is the symbol for a gamma ray?
During gamma decay, the number of protons
number of neutrons
, and the
.
Write the complete equation for the gamma decay of titanium-44:
Copyright © 2009 by Nelson Education Ltd.
Chapter 10 Blackline Master 10.3-2
31
Blackline Master 10.4-1
Name:
Date:
Radioactive Decay and Half-Life
Consider a sample of matter containing radioactive material. The sample initially contains
16 radioactive nuclei. The half-life of the parent isotope is 10 minutes.
At the start, the sample has 16 parent
nuclei and no daughter nuclei.
During the first 10 minutes, half the
parent nuclei decay:
16
2
8 parent nuclei remaining
After 10 minutes, 50 % of the original
parent nuclei remain.
During the next 10 minutes, half the
remaining parent nuclei decay:
During the next 10 minutes, half the
parent nuclei decay:
8
4
2
4 parent nuclei remaining
After 20 minutes, 25 % of the original
parent nuclei remain.
32
Chapter 10 Blackline Master 10.4-1
2
2 parent nuclei remaining
After 30 minutes, 12.5 % of the original
parent nuclei remain.
Copyright © 2009 by Nelson Education Ltd.
Blackline Master 10.4-2
Name:
Date:
Radioactivity Concept Map
Complete the concept map to show the relationships among the Chapter 10 vocabulary.
Begin with the box that has already been filled in.
radioactivity
nucleus
protons
neutrons
isotopes
radioactive decay
parent nucleus
daughter nucleus
alpha particle
radioactivity
involves
changes in
an atom’s
beta particle
gamma ray
half-lives
decay series
Atoms with the same
number of protons but
different numbers of
which is
made up of
are called
some of which have
unstable nuclei, causing
them to undergo
during
which a
which can involve
elements with different
may emit radiation in
the form of a(n)
which may decay
further to form
another daughter
nucleus as part of a
to produce
a
Copyright © 2009 by Nelson Education Ltd.
Chapter 10 Blackline Master 10.4-2
33
Chapter 10: Radioactivity BLM and WS Answer Key
BLM 10.0-1 Radioactivity Concept Map
radioactivity
involves
changes in
an atom’s
nucleus
Atoms with the same
number of protons but
different numbers of
which is
made up of
neutrons
protons
are called
some of which have
unstable nuclei, causing
them to undergo
radioactive decay
during
which a
isotopes
which can involve
elements with different
parent nucleus
half-lives
decay series
may emit radiation in
the form of a(n)
which may decay
further to form
another daughter
nucleus as part of a
alpha
particle
beta
particle
or
to produce
a
gamma
ray
BLM 10.3-2 Writing Nuclear Equations
1. 42He; 86; 86; 217; 131; decreases; 2; decreases; 4;
217
213
4
86Rn
84Po 2He
៮៬
2. 17; 17; 42; 42; 25; increases; stays the same;
42
42
0
71Cl
18Ar 1e
៮៬
34
Unit C: Radioactivity
daughter
nucleus
3. 47; 47; 106; 59; increases; stays the same;
106
106
0
47Ag
48Cd 1e
៮៬
0
4. 22; 22; 44; 22; 0; stays the same; stays the same;
44
44
0
22Ti*
22Ti 0
៮៬
NEL
WS 10.4-3 Half-Life Calculations
1. (a)
152 d
38 d/half-life
WS 10.0-1 Matching Challenge: Radioactivity
1. (e); 2. (g); 3. (i); 4. (c); 5. (l); 6. (f );7. (j); 8. (b); 9. (a);
10. (d); 11. (k); 12. (h)
4 half-lives
(1296 Bq) 冢 24 冣 (1296) 冢 16 冣 81 Bq
(b)
1
1
38 d/half-life
5 half-lives
190 d
(25)(1296 Bq) 41 472 Bq
(c)
324 Bq
1296 Bq
0.25 1
4
1
22
The activity
will be 324 Bq in two half-lives, or 76 d.
2. (a) approximately 18 hr
(b)
72 Hr
18 Hr
4 half-lives
(5 108) 冢 24 冣 (5 108) 冢 16 冣 ⬇ 3 107 atoms
1
1
WS 10.4-4 Tech Connect: Brachytherapy
1. (c); With other types of radiation therapy, radiation has
to penetrate healthy tissues to reach a tumour,
damaging many healthy cells in the process.
2. (c); Radioactive isotopes used in the body need to
decay quickly enough so that the body does not
experience long-term exposure to concentrated
sources of radiation. Seconds or microseconds
would be too short for the radiation to have the
desired effect.
3. (d); If the half-life of the radioactive isotope is long
enough, the sample can be reused for other
patients.
NEL
Chapter 10 Quiz
Part A: Modified True/False
1. True
2. False; possible responses: mass number, numbers of
neutrons, radioactive particles
3. False; 4
Part B: Completion
4. electrons
5. 122
6. excited
Part C: Matching
7. (c); 8. (a); 9. (b)
Part D: Multiple Choice
10. A; 11. D; 12. B; 13. D; 14. A;
15. D; 16. B; 17. B
Part E: Short Answer
18. (a) The nucleus consists of protons and neutrons, but
no electrons. (b) During beta decay a neutron
breaks down and turns into a proton, an electron,
and a neutrino. The proton stays in the nucleus.
The electron and neutrino are emitted.
121
0
19. 121
50Sn
51Sb 1e
៮៬
Chapter 10 Answer Key
35