Download Teacher Materials - Scope, Sequence, and Coordination

Scope, Sequence & Coordination
A National Curriculum Development and Evaluation Project for High School Science Education
A Project of the National Science Teachers Association
This project was suppported in part by the National Science Foundation.
Opinions expressed are those of the authors and not necessarily those of the Foundation.
The SS&C Project encourages reproduction of these materials for free distribution.
Scope, Sequence & Coordination
SS&C Research and Development Center
Iowa Coordination Center
Bill G. Aldridge, Principal Investigator
and Project Director*
Dorothy L. Gabel, Co-Principal Investigator
Erma M. Anderson, Associate Project Director
Nancy Erwin, SS&C Project Editor
Rick McGolerick, Project Coordinator
Robert Yager, Center Director
Keith Lippincott, School Coordinator
University of Iowa, 319.335.1189
Evaluation Center
Frances Lawrenz, Center Director
Doug Huffman, Associate Director
Wayne Welch, Consultant
University of Minnesota, 612.625.2046
Houston SS&C Materials Development and
Coordination Center
Linda W. Crow, Center Director
Godrej H. Sethna, School Coordinator
Martha S. Young, Senior Production Editor
Yerga Keflemariam, Administrative Assistant
Baylor College of Medicine, 713.798.6880
Houston School Sites and Lead Teachers
Jefferson Davis H.S., Lois Range
Lee H.S., Thomas Goldsbury
Jack Yates H.S., Diane Schranck
Iowa School Sites and Lead Teachers
Pleasant Valley H.S., William Roberts
North Scott H.S., Mike Brown
North Carolina Coordination Center
Charles Coble, Center Co-Director
Jesse Jones, Center Co-Director
East Carolina University, 919.328.6172
North Carolina School Sites and Lead Teachers
Tarboro H.S., Ernestine Smith
Northside H.S., Glenda Burrus
Puerto Rico Coordination Center**
Manuel Gomez, Center Co-Director
Acenet Bernacet, Center Co-Director
University of Puerto Rico, 809.765.5170
Puerto Rico School Site
UPR Lab H.S.
California Coordination Center
Tom Hinojosa, Center Coordinator
Santa Clara, Calif., 408.244.3080
California School Sites and Lead Teachers
Lowell H.S., Marian Gonzales
Sherman Indian H.S., Mary Yarger
Sacramento H.S., Brian Jacobs
Pilot Sites
Site Coordinator and Lead Teacher
Fox Lane H.S., New York, Arthur Eisenkraft
Georgetown Day School, Washington, D.C.,
William George
Flathead H.S., Montana, Gary Freebury
Clinton H.S., New York, John Laffan**
Advisory Board
Dr. Rodney L. Doran (Chairperson),
University of Buffalo
Dr. Albert V. Baez, Vivamos Mejor/USA
Dr. Shirley M. Malcom, American Association
for the Advancement of Science
Dr. Shirley M. McBay, Quality Education for Minorities
Dr. Mary Budd Rowe, Stanford University
Dr. Paul Saltman, University of California, San Diego
Dr. Kendall N. Starkweather, International
* Western NSTA Office, 394 Discovery Court, Henderson, Nevada 89014, 702.436.6685
** Not part of the NSF-funded SS&C project.
Technology Education Association
Dr. Kathryn Sullivan, NOAA
National Science Education Standard—
Physical Science and Earth and Space
Teacher Materials
Learning Sequence Item:
966
Structure of Atoms
The nuclear forces that hold the nucleus of an atom together, at nuclear
distances, are usually stronger than the electric forces that would make it
fly apart. Nuclear reactions convert a fraction of the mass of interacting
particles into energy, and they can release much greater amounts of energy than atomic interactions. Fission is the splitting of a large nucleus
into smaller pieces. Fusion is the joining of two nuclei at extremely high
temperature and pressure, and is the process responsible for the energy
of the sun and other stars.
Radioactive isotopes are unstable and undergo spontaneous nuclear reactions, emitting particles and/or wave-like radiation. The decay of any
one nucleus cannot be predicted, but a large group of identical nuclei
decay at a predictable rate. This predictability can be used to estimate the
age of materials that contain radioactive isotopes.
Energy in the Earth System
Two primary sources of internal heat (as Earth’s sources of energy) are
the decay of radioactive isotopes and gravitational energy from the Earth’s
original formation.
Radioactivity, Time
and Age
March 1996
Adapted by: Nancy Reclusado, Don Warner,
Dorothy Gabel, Thomas Goldsbury and
Linda W. Crow
The Origin and Evolution of the Universe
Early in the history of the universe, matter, primarily the light atoms
hydrogen and helium, clumped together by gravitational attraction to form
countless trillions of stars. Billions of galaxies, each of which is a gravitationally bound cluster of billions of starts, now form most of the visible
mass in the universe.
Stars produce energy from nuclear reactions, primarily the fusion of hydrogen to form helium. These and other processes in stars have led to the
formation of all the other elements.
Radioactivity and its Applications. (a) Students should develop an understanding of average lifetime for a radioactive material expressed in terms
of half-life (1.433T1/2). They should use results of such calculations for various radioactive materials to consider implications for radioactive wastes.
(Chemistry, A Framework for High School Science Education, p. 81.)
Earth’s Internal Energy Sources: Radioactivity and Gravitational Potential Energy. (b) Students should be able to use radioactive count data in
a graph to determine half-life and mean lifetime of a radioactive sample. (Earth and Space Sciences, A Framework for High School Science Education,
p. 135.)
Nuclear Fission and Fusion. (c) Students should create and examine macroscopic analogs to chain reactions, like mousetrap/Ping Pong ball
arrangements, to gain the concept of a chain reaction. (Chemistry, A Framework for High School Science Education, p. 79.)
Origin and Age of Earth: Rock Sequences, Fossils, and Radioactive Dating: (d) Students should learn to use the concept of geologic time in
relationship to fossils. (Earth and Space Sciences, A Framework for High School Science Education, p. 149.)
Contents
Matrix
Suggested Sequence of Events
Lab Activities
1. Stand 'Em Up, Knock 'Em Down
2. Snapping Traps
3. Crumpled Paper
4. Light My Fire
5. Radioactivity
6. "Seeing" the Invisible
7. Half-life of Peas
8. Getting Shorter All the Time
9. Rocks with a Past
Continued
This microunit was adapted by Nancy Reclusado (Sacramento H.S., Sacramento, Calif.), Don Warner (Sacramento H.S., Sacramento),
Dorothy Gabel (Indiana Univ., Bloomington), Thomas Goldsbury (Lee H.S., Houston, Texas), and
3 of Medicine, Houston)
Linda W. Crow (Baylor College
Contents (continued)
Lab Activities
10. The Case of the Melting Ice
Assessment
1. Bowling
2. Nuclear Weapons
3. Science or Alchemy?
4. Radiation, I
5. Bean Counters
6. Eating the Difference
7. Radioactive Controls
8. Radiation, II
9. Age Correlations, I
10. Age Correlations, II
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Learning Sequence
Radioactivity and its Applications. (a) Students should develop an understanding of average lifetime for a radioactive material
expressed in terms of half-life (1.433T1/2). They should use results of such calculations for various radioactive materials to
consider implications for radioactive wastes. (Chemistry, A Framework for High School Science Education, p. 81.) Earth’s
Internal Energy Sources: Radioactivity and Gravitational Potential Energy. (b) Students should be able to use radioactive
count data in a graph to determine half-life and mean lifetime of a radioactive sample. (Earth and Space Sciences, A Framework
for High School Science Education, p. 135.) Nuclear Fission and Fusion. (c) Students should create and examine macroscopic
analogs to chain reactions, like mousetrap/Ping Pong ball arrangements, to gain the concept of a chain reaction. (Chemistry, A
Framework for High School Science Education, p. 79.) Origin and Age of Earth: Rock Sequences, Fossils, and Radioactive
Dating: (d) Students should learn to use the concept of geologic time in relationship to fossils. (Earth and Space Sciences, A
Framework for High School Science Education, p. 149.)
Science as Inquiry
Stand 'Em Up, Knock 'Em Down
Activity 1
Snapping Traps
Activity 2
Science in Personal
and Social Perspectives
Science and Technology
Chain Reaction:
The First Half-Century
Reading 1
The Birth of the Nuclear Age
Reading 2
Bowling
Assessment 1
Science or Alchemy?
Assessment 3
Nuclear Weapons
Assessment 2
Marie Curie: A Pioneer
in the Study of
Radioactivity
Reading 3
Crumpled Paper
Activity 3
Radiation, II
Assessment 8
Light My Fire
Activity 4
Chain Reaction:
The First Half-Century
Reading 1
Radioactivity
Activity 5
The Birth of the Nuclear Age
Reading 2
"Seeing" the Invisible
Activity 6
Half-Life of Peas
Activity 7
Getting Shorter All the Time
Activity 8
Rocks With A Past
Activity 9
The Case of the Melting Ice
Activity 10
Radiation, I
Assessment 4
Bean Counters
Assessment 5
Eating the Difference
Assessment 6
Radioactive Controls
Assessment 7
Age Correlations, I
Assessment 9
Age Correlations, II
Assessments 10
The Dating Game
Reading 6
5
History and Nature
of Science
Madame Curie and
Radioactivity
Reading 5
Modern Alchemy
Reading 6
Suggested Sequence of Events
Event #1
Lab Activity
1. Stand 'Em Up, Knock 'Em Down
Event #2
Lab Activity
2. Snapping Traps
Event #3
Lab Activity
3. Crumpled Paper
Event #4
Lab Activity
4. Light My Fire
Event #5
Lab Activity
5. Radioactivity
Event #6
Lab Activity
6. "Seeing the Invisible
Event #7
Lab Activity
7. Half-life of Peas
Alternative or Additional Activities
8. Getting Shorter All the Time
Event #8
Lab Activity
9. Rocks with a Past (55 minutes)
Event #9
Lab Activity
10. The Case of the Melting Ice (55 minutes)
Event #10
Readings from Science as Inquiry, Science and Technology, Science in Personal and Social Perspectives,
and History and Nature of Science
Reading 1
Reading 2
Reading 3
Reading 4
Reading 5
Reading 6
Chain Reaction: The First Half-Century
The Birth of the Nuclear Age
Marie Curie: A Pioneer in the Study of Radioactivity
The Dating Game
Madame Curie and Radioactivity
Modern Alchemy
Readings can be found in the student version of this publication.
Assessment items are at the back of this volume.
6
Assessment Recommendations
This teacher materials packet contains a few items suggested for classroom assessment. Often, three
types of items are included. Some have been tested and reviewed, but not all.
1. Multiple choice questions accompanied by short essays, called justification, that allow teachers to
find out if students really understand their selections on the multiple choice.
2. Open-ended questions asking for essay responses.
3. Suggestions for performance tasks, usually including laboratory work, questions to be answered,
data to be graphed and processed, and inferences to be made. Some tasks include proposals for
student design of such tasks. These may sometimes closely resemble a good laboratory task, since
the best types of laboratories are assessing student skills and performance at all times. Special
assessment tasks will not be needed if measures such as questions, tabulations, graphs, calculations,
etc., are incorporated into regular lab activities.
Teachers are encouraged to make changes in these items to suit their own classroom situations and to
develop further items of their own, hopefully finding inspiration in the models we have provided. We
hope you may consider adding your best items to our pool. We also will be very pleased to hear of
proposed revisions to our items when you think they are needed.
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Activity 1
Teacher Sheet
Science as Inquiry
Stand ‘Em Up, Knock ‘Em Down
How do dominoes simulate nuclear fission?
Overview:
Students set up a chain reaction with dominoes.
Materials:
Per lab group:
25 dominoes per group of four
1 large table or floor space
1 stopwatch or clock with second hand
Procedure:
Have students set up the dominoes in two different arrangements—a straight line and as shown in the
figure below.
Students measure how long it takes for the entire arrangement of dominoes to fall over and record their
data for each design. They then compare the number of dominoes being knocked over per second
according to the design. Finally, have students make a sketch of their design.
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Activity 1
Background:
If you gave the flu to two people, they could give the flu to two more people, who would continue to
share the flu with others. You would set off a chain reaction. A unique result of fission is the release of
two or three neutrons from the nucleus. Neutrons begin the fission process by splitting nuclei, and
splitting nuclei keep the reaction going by releasing more neutrons.
“Expanding” chain reactions are out of control; “limited” chain reactions are controlled. Expanding
chain reactions characterize nuclear weapons, where a lot of energy is released in a short period of time.
Limited chain reactions are found in a nuclear plant, where the energy released is under control and
released over a longer time period. When you control the rate of fission in a chain reaction, the heat
released can be used to generate electricity.
Further Variations:
Have students design a different way of modeling this process.
Adapted from American Chemical Society, "Chemistry in the Community," Chem Com, 2nd edition.
Kendall Hunt, 1993.
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Activity 2
Teacher Sheet
Science as Inquiry
Snapping Traps
How do snapping mousetraps simulate a nuclear chain reaction?
Overview:
Students set up linked mousetraps that simulate a nuclear reaction.
Materials:
Per lab group:
7 mouse traps
4 ft. of string
stop watch or clock with second hand
Procedure:
Have students attach the mousetraps together with string. The strings from the gate of the first trap
can be attached to one or two triggers of one or more traps. Continue until all the mousetraps have been
used (see figure).
The strings need to be fairly taut, otherwise the first trap may not spring the others. Students should
design and set off at least two different arrangements, timing how long each reaction took and the
number of traps that sprang.
Background:
By setting off mousetraps, you can demonstrate how the fission of one nucleus emits neutrons that
can cause fission of other nuclei. “Expanding” chain reactions are out of control; “limited’ chain reactions are controlled. Before a chain reaction occurs, a large enough mass of fissionable material must be
present in order for sufficient neutrons to be captured to sustain the reaction. This is called the critical
mass.
Caution: Mousetraps are extremely sensitive. Do not place fingers in the way of the gate.
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Activity 2
Further Variations:
The class can work as a whole to demonstrate a dynamic result.
Adapted from Wind, Water, Fire and Earth, NSTA,1986.
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Activity 3
Teacher Sheet
Science as Inquiry
Crumpled Paper
How can crumpled paper be used to illustrate
a nuclear chain reaction?
Overview:
Illustrate a chain reaction by having students throw wads of paper in turn as each is hit with a wad.
Materials:
Per class:
two pieces of paper per student
Procedure:
Each student, and you, has two pieces of paper he or she crumples. Instruct students to stand and shut
their eyes. Begin the chain reaction by standing in the same direction as the students and throwing your
paper wads over your shoulder in their direction. If hit by a wad, a student must toss his/her paper wads
in any direction. It normally takes a few attempts to get this started and dies out before all students are
hit by a crumpled paper wad.
Repeat the process after students have moved closer together. Relate this to the critical mass needed
for a sustained nuclear reaction. Have students diagram the positions of the participants at the beginning
of the activity and again at the end.
Background:
Nuclear fission occurs when a large atom is split into two fragments of about the same mass. A
unique result of fission is the release of two or three neutrons from the nucleus. Since neutrons begin the
fission process, splitting nuclei keep the reaction going by releasing more neutrons. “Expanding” chain
reactions are out of control; “limited” chain reactions are controlled.
Expanding chain reactions characterize nuclear weapons, where a lot of energy is released in a short
period of time. In order for a chain reaction to begin, enough neutrons must be captured by the surrounding atoms. This is called the critical mass of the substance. Limited chain reactions occur in a nuclear
plant, where the energy released is under control and released over a longer time period. When you
control the rate of fission in a chain reaction, the heat released can be used to generate electricity.
Adapted from American Chemical Society, "Chemistry in the Community," Chem Com, 2nd edition.
Kendall Hunt, 1993.
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Activity 4
Teacher Sheet
Science as Inquiry
Light My Fire
How does a spreading fire simulate nuclear fission?
Overview:
In this demonstration, students set up and light matches to simulate a chain reaction.
Materials:
Demonstration per class:
3 or 4 lids from shoe boxes
1 small nail
1 box of wooden matches
1 metal container to extinguish the flames
Warning: Make certain the metal container completely covers this demonstration before you start.
Procedure:
With a small nail, students punch a square pattern of holes about one centimeter apart from one
another in a shoe box lid (see figure).
They plug the holes with wooden matches and light one corner match. That match will set off the rest (a
chain reaction). Make sure that the metal container completely covers the demonstration so the flames
can be easily extinguished. Try other arrangements and distances.
Further Variations:
This should be done as a demonstration. You might want to make a permanent demonstration board
out of wood in which you drill holes for the matches.
Background :
Fission (splitting apart) of one nucleus emits neutrons than can split apart other nuclei—a chain
reaction. A critical mass of the fissionable material must be present so that sufficient neutrons are
captured to create the sustainable chain reaction.
Adapted from Christensen, J.W. Energy Resources and Environment, Iowa: Kendall Hunt, 1981.
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Activity 5
Teacher Sheet
Science as Inquiry
Radioactivity
Materials:
Per lab group:
100 pennies
shoe box with lid
graph paper
Procedure:
Students place pennies “heads-down” in a shoe box, cover the box with the lid and shake it. They
open the box and remove all the “changed” pennies (those that landed “heads-up”). Students count the
number of “unchanged” pennies remaining in the box and record this information on a data table. Students repeat the procedure until all the pennies have changed, recording each trial and each result.
Background:
The nuclei of radioactive atoms break down, releasing particles and radiation. Radioactive decay goes
on like clockwork, at an even and continuous pace. As the nuclei of radioactive atoms break down, the
radioactive element changes to a stable new element.
The rate of radioactive decay is measured by half-life—the time it takes for half of the parent element
to change into atoms of the daughter element. The element radium-126, has a half-life of 1,622 years.
What happens to 20 grams of radium after 1,622 years? Ten grams of radium remain, and 10 grams have
changed into lead.
Variations:
Use M&Ms or brass fasteners in place of the pennies.
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Activity 6
Teacher Sheet
Science as Inquiry
"Seeing" the Invisible
Can scientists see the particles emitted by radioactive substances?
Demonstration
Materials:
cloud chamber
10 mL isopropyl alcohol
1 lb dry ice ice (thin slab)
high intensity light (20+ watt)
squeeze bottle (for alcohol)
1 pr disposable gloves
crucible tongs
radiation source or Colman Lantern mantle
flashlight with tape
Procedure:
In order to see while fog is produced in the cloud chamber, 1) paint the bottom of the chamber black,
and 2) prepare a high intensity light source by covering a flashlight with tape—leaving a small hole
(pencil-sized) for light to shine through. Wearing heavy gloves and using
forceps, wet the felt band encircling the inside top of the chamber with
alcohol. Insert the radioactive source into the chamber by placing it on the
end of the needle projecting into the chamber. The needle should be supported by a cork stopper inserted into a hole in the wall of the cylinder. (If
using the Colman Lantern mantle, rest it on the bottom of the cylinder.)
Cover the cylinder. To minimize student contact with the radiation source,
place the source in the cloud chamber prior to class. Set the chamber on the
smooth block of dry ice. (If block-dry ice is not available, crush the ice
pellets so that the surface is even and there is good contact between the
cylinder and the surface of the dry ice.) Turn on the light source—from the
Sample tracks (in reverse) in
side of the chamber—and note the tracks that are emitted from the radioactive
a cloud chamber.
source.
The tracks must be viewed from the top, so only a few students at a time
can gather around the chamber to view them. An alternative is to have one cloud chamber for each group
of students. Note: students should not handle or touch the radioactive source—these should be in place
before class begins.
Cloud chamber kits and radiation sources may be purchased from Sargent-Welch. For best observation,
the room should be darkened and the light source directed into the side of the chamber.
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Activity 6
Background:
Elements occurring in nature that are radioactive emit alpha, beta and gamma radiation. Alpha
particles are actually the nuclei of helium atoms containing two neutrons and two protons. They usually
travel only a few centimeters through air before being absorbed. Moving at relatively slow speeds (about
1/10 the speed of light), they ionize the air as they pass through it—but can be stopped by a single sheet
of paper or deflected by a magnet.
Beta particles are electrons. Because of their negative charge, they also can be deflected by magnets.
They move at the speed of light, have a greater penetrating power than alpha particles—but do not
readily ionize air. They can be stopped by a thin sheet of aluminum.
Gamma radiation is a type of radiation similar to X-rays, but with greater penetrating power than
either x-rays, alpha particles or beta particles. Gamma rays ionize atoms they strike, can be stopped by
several centimeters of lead—and because they are not charged, are not deflected by magnets.
The major source of radioactivity that is seen in the cloud chamber is due to alpha particles, although
some beta particles are undoubtedly being emitted. Differences in the intensity of the tracks are due
primarily to the difference in the mass of the alpha particles (He nuclei) and, hence, lower speed vs. beta
particles (electrons). Differences in direction and length can also be due to variations in temperature and
degree of saturation with alcohol vapor.
The tracks that form are actually clouds of alcohol that form on the particles being emitted from the
radioactive source. As the dry ice sublimes, it absorbs heat from the air in the chamber creating a very
cool environment. This allows more alcohol vapor to evaporate forming a supersaturated gaseous solution. As the particles are emitted from the radioactive source, this solution is disturbed and the excess
alcohol forms on the particles—and is seen in the form of clouds.
Adapted from:
Haberschaum, et al., IPS, 4th Ed., Prentice-Hall, 1982.
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Activity 7
Teacher Sheet
Science as Inquiry
Half-Life of Peas
Can the half-life of a radioactive element be illustrated with peas?
Materials:
Per lab group:
1 cup split peas
empty cup
tray (or piece of paper)
clock with second-hand
Procedure:
Students first count the number of peas or “atoms” in their cup and record this number as the initial
number of radioactive atoms. After noting the time, students pour the cup full of peas into a tray (or onto
a piece of paper). They then separate them into two categories, radioactive or decayed (or stable). If the
flat side of the pea is up, the “atom” is still radioactive. These radioactive atoms are counted, recorded
under “Trial 1” on a data table, and placed back in the now empty cup. If the flat side of the pea is down,
then the atom has decayed. These decayed atoms are placed in the other cup. Students repeat the process
by emptying the cup of radioactive atoms on the tray, removing the decayed atoms (adding them to the
cup of decayed atoms from Trial 1), counting the radioactive atoms, and recording the results under
“Trial 2.” This sequence is repeated until no more radioactive atoms remain. The final time and total time
are then recorded. The students will need to set up a data table similar to the one below:
Trial number
Number of Radioactive Atoms
0
1
2
3
4
5
6
[etc.]
Initial atoms in cup
Initial time:
Final time:
Total time (in sec.):
When the activity is completed students calculate the half-life of their peas by dividing the total
time in seconds by the number of trials it took until all of the atoms had decayed (become stable).
Students also make a graph of the half-life versus the number of radioactive atoms present at each
half-life interval.
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Activity 7
Background:
The half-life of a radioactive element is the time it takes for half the nuclei present to decay. The
amount of that nucleus remaining is halved after each half-life. The half-life of an isotope of an element
is not changed by changes in temperature or pressure, and different isotopes of a given element have
different half-lives or may be stable and not disintegrate. For example, Be-10 has a half-life of 1.6 ¥ 106
years whereas B-8 has a half-life of 6.7 ¥ 10-17 seconds. C14 which is used in radiocarbon dating has a
half life of 5,730 years, After carbon-14 decays to nitrogen-14, the carbon is not longer present. Hence an
analysis of changes of mass of carbon-14 present in a given sample of a substance can be used to calculate the age of the substance.
A material containing 1 gram of carbon-14 in the year 2000 will contain 1/2 gram 5,730 years from
the year 2000, and 1/2 of 1/2 gram (or 1/4 gram) in 13,460 A.D. graph paper
Adapted from:
Nancy Russo.
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Activity 8
alternative/extension activity for Event 7
Teacher Sheet
Science as Inquiry
Getting Shorter All the Time
Can the half-life of a radioactive element be illustrated with licorice?
Materials:
Per lab group:
length of licorice (vine type or whip—the longer the better)
scissors (or knife—to cut licorice)
metric ruler
paper towel (to put licorice on)
clock with second-hand
Procedure:
Students measure and record the length of the entire piece of licorice. They also note the beginning
time to the nearest second. They then cut the piece of licorice in half and record the trial number and the
remaining length. (They may eat the other half or save it and form a licorice graph.) It represents the
mass of the radioactive element that has disintegrated. With the remaining piece, students repeat the
halving process, recording the length and trial number until the remaining piece is too small to be cut in
half. Students then record the final time.
Trial number
Length of Licorice
0
1
2
3
4
5
6
[etc.]
Initial length
Initial time:
Final time:
Total time (in sec.):
When the activity is completed the groups calculate the half-life of the licorice by dividing the total
time in seconds by the number of trials it took until all of the licorice had become stable (decayed or was
eaten). Students also make a graph of the half-life versus the number of radioactive length present at each
half-life interval.
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Activity 8
Background:
The half-life of a radioactive element is the time it takes for half the nuclei present to decay. The
amount of that nucleus remaining is halved after each half-life. The half-life of an isotope of an element
is not changed by changes in temperature or pressure, and different isotopes of a given element have
different half-lives or may be stable and not disintegrate. For example, Be-10 has a half-life of 1.6 x 106
years whereas B-8 has a half-life of 6.7 x 10-17 seconds. C-14 which is used in radiocarbon dating has a
half life of 5730 years, After carbon-14 decays to nitrogen-14, the carbon is not longer present. Hence an
analysis of changes of mass of carbon-14 present in a given sample of a substance can be used to calculate the age of the substance.
A material containing 1 gram of carbon-14 in the year 2000, will contain 1/2 gram 5,730 years from
the year 2000, and 1/2 of 1/2 gram (or 1/4 gram) in 13,460 AD.
Adapted from:
SS&C, Bozeman participant Carole Magnussen.
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Activity 9
Teacher Sheet
Science as Inquiry
Rocks With a Past
What do rocks look like that can be radioactive?
Overview:
This simple, observational activity provides students some direct experiences with rocks that can be
used in the radioactive dating process.
Materials:
Per class:
Samples of:
charcoal
tuff
volcanic ash
monzonite
quartz monzonite
granite
rhyolite
gneiss
magnifying glasses (or hand lenses)
Procedure:
Have students examine these different rocks. Tell them that these are the rocks that can be used in
radioactive dating. The students will describe the rocks, determine its density and also used rock keys to
identify their component parts. A rock key has been included for your use with these rock types. Also
have them associate a rock type with each of these samples . You may want to emphasize the color and
texture for igneous rocks. Keep in mind that color is related to the amount of quartz (light-colored) and
the amount of the ferromagnesium minerals (dark-colored). Texture refers to the size of the grains and is
directly related to cooling time. Please note that igneous and metamorphic rocks are the primary rocks
used for this dating process. A good question to pose is why these particular rocks are the ones that can
be used in this process?
Background:
Determining the age of rocks using radioactive dating is simple in theory, but in practice it becomes
very difficult. The difficulty lies primarily in measuring the very tiny amounts of the isotopes. When
possible, two or more methods of analysis are used on the same rock specimen to
crosscheck the results.
The potassium-argon method is often used to determine ages of most rocks samples. The rocks used
in this lab have the minerals that contain this important combination.
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Activity 9
Variations:
Relative time and the use of sedimentary rocks could be added to this lab to connect the use of
absolute and relative time techniques.
IGNEOUS ROCKS
Composition
and
Color
Texture
Very coarse-grained
Light
Intermediate
Dark
Very Dark
10–20% quartz
no quartz
no quartz
10% ferromagnesian
minerals
25–40% ferromagnesian
minerals
50% ferromagnesian
minerals
100% ferromagnesian
minerals
pegmatite
—
—
—
Coarse-grained
granite
diorite
gabbro
peridotite
Fine-grained
rhyolite
andesite
basalt
—
Glassy
obsidian
Frothy or cellular
pumice
—
scoria
Volcanic tuff (fragments <4 mm)
Pyroclastic or fragmental
Volcanic breccia (fragments >4 mm)
METAMORPHIC ROCKS
Foliated Rocks
Crystal size
Rock name
Very fine, not visible
Fine grains, not visible
Coarse, visible with unaided eye;
mostly micaceous minerals
slate
phyllite
Coarse
gneiss
s
c
h
i
s
t
Comments
muscovite schist
biotite schist
garnet schist
staurolite schist
kyanite schist
sillimanite schist
Cleavage crosses sedimentary layers
Foliation well developed; rock has “sheen”
Types of schist, recognized on mineral content,
reflect increasing intensity of metamorphism from
top downward
Well-developed color banding or streaking
Nonfoliated Rocks
Precursor rock
quartz sandstone
limestone
conglomerate
basalt or gabbro
Metamorphic rock name
quartzite
marble
stretched-pebble
conglomerate
greenstone
amphibolite
Comments
Composed of interlocking quartz grains
Composed of interlocking calcite grains
Original pebbles distinguishable, but strongly
deformed
Composed of epidote and chlorite
Composed of amphibole and plagioclase
Adapted from:
Crow, Linda W., "Rock of Ages," Geologic Methods, 1988.
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Activity 10
Teacher Sheet
Science as Inquiry
The Case of the Melting Ice
How is the transition of ice to water like the radioactive decay of materials?
Materials:
Per lab group:
ring stand setup
funnel
graduated cylinder
ice
Procedure:
The following is a creative and memorable way to introduce the concept of decay and mother/daughter relationship (in this case, ice and water) as well as establish an analogy to radiometric dating. It is
purely qualitative and introductory—and can be a lot of fun.
Set up each lab station as shown and fill the funnel with ice at least 1/2 hour before class starts. Note
the time at which this is done, but do not reveal this time to the students until the end of the activity. As
soon as students enter the room, have them take note of the time and volume of water in their graduated
cylinder. Tell them that they are detectives working on the murder of Frosty the Snowman—and that it is
crucial to know the exact time of the placement of the ice so alibis can be checked. Students should
determine a time interval and record the volume of water at each interval on a chart until the ice is nearly
(not completely) melted. They will record this information as points on a “time vs. volume” graph (a
reasonably linear plot will emerge after about 45 minutes), and working backwards, determine the exact
time the ice was placed in the funnel (time-zero, when the volume was zero)—or the exact time of the
crime. Set up a competition among the lab groups to see which group comes closest to time-zero.
While waiting for the decay curve to be determined, discuss how any dating system can work by
projection of the product vs. time curve back to the time of zero progeny; the assumptions involved in
this system (i.e., constant room temperature, closed- or open-system, melting occurring at a constant rate,
etc.); and/or what factors in this investigation have direct analogies to radiometric dating.
Background:
The most important concept for the student to grasp is the ability to project the “decay curve” back to
time-zero. The time vs. volume plot of melting ice is linear. There are, however, some factors which will
skew the plot. The key factor in determining the rate of melting is the rate of heat transfer from the
surroundings through the funnel to the ice. Until the system has reached thermal equilibrium, the “decay”
will be non-linear. This is the reason for placing the ice in the funnel at least 1/2 hour before class starts.
Only late in the melting process (when too little ice remains to keep the funnel at constant temperature)
does the temperature of the funnel rise and the rate of heat transfer to the surroundings drop.
Large volume, thin-walled, thermally conductive (metal) funnels work best. It is a good idea to
“super-cool” the ice and allow as little time as possible between removing the ice from the freezer and
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Activity 10
filling the funnels. As the students are doing the graph, lead them in choosing a large enough vertical
scale to produce a steep slope to facilitate the projection back to time-zero.
After the investigation, after the basic discussion of how to use the time vs. progeny plot is completed, the class can be led to the assumptions being made the the analogous assumptions required to
date, for example, a uranium mineral having radiogenic lead in it. For example:
Parent and progeny represent a direct transition of one form to another. Ice converts to water and uranium238 converts to lead206.
This is a closed system. Nothing escaped and nothing was added. Only with this assumption is it
possible to calculate time-zero when no progeny were present.
All the water in the cylinder came from the melting of the ice. Was there condensation on the outside
of the funnel? Did it drop into the graduated cylinder? Was this significant?
Evaporation and sublimation of ice and water are negligible. Did the cylinder leak? Did anyone
remove any melt water or ice? (In a uranium-bearing rock, this requires that none of the uranium or lead
was dissolved or diffused out of the rock.)
The rate of change from parent to progeny can be determined. Of course, the rate of change of
melting ice is relatively linear whereas that of radioactive decay is exponential.
Variations:
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Assessment 1
Science in Personal and Social Perspectives
Bowling
Item:
Bowling is a recreational game for many people and a profession for a few. The ideal object of the
game is to knock down all ten pins each time you throw/roll the ball down the lane. There are 10 frames/
times that you get to accomplish this task in one game. You do get a second chance in each frame to
knock the pins down if you were not successful with the first ball. A score is kept to acknowledge a
winner. (Bowling models a chain reaction.) Explain in writing how bowling could be an “expanding” or
“limited” model of a chain reaction.
Answer:
At specific times bowling is expanding, limited, or both. An expanding chain reaction would be when
all 10 pins are knocked down at one time (uncontrolled pin action; the reaction happens in a short period
of time). A score of 300 is the expanding chain reaction goal. A limited chain reaction occurs when only
a few of the original 10 pins are knocked down. This is a controlled reaction and takes a longer period of
time.
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Assessment 2
Science in Personal and Social Perspectives
Nuclear Weapons
Item:
Nuclear weapons have been a controversial worldwide issue. Leaving aside the moral issue of devastation or no devastation, you need to make a plan for the use of an atomic bomb. You will be bombing an
imaginary target area (no people) of 100 square miles. Decide how to deliver the bomb and where to
detonate it. Outline your plan on paper and explain what will happen.
Answer:
Firebombing checklist:
1. Airplane—not a taxi; fueled, recent checkup.
2. Pilot—20/20 vision; top gun trained.
3. Map to imaginary target.
4. Strategy
a. Size of atomic bomb—determined by area detonation will destroy.
b. Time—day and hour.
c. Weather forecast.
d. Location of drop.
1. Detonate above the ground because you want as much
fissionable material available as possible to carry out the chain reaction.
2. Do not detonate on the ground because the ground could stop
the chain reaction.
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Assessment 3
History and Nature of Science
Science or Alchemy?
Item:
During the early years of the 20th century, the Curies, Rutherford and many other scientists were
working on the nature of radioactivity. At one meeting between these scientists, Rutherford said that he
thought that radioactivity was a “nuclear property.” Madame Curie was heard to respond, “Dr. Rutherford, do you believe in science or alchemy?”
Noting Madame Curie’s response to Dr. Rutherford, explain what she was saying and why her comment was relative at the time. In terms of what is known today, who was correct? Explain your answer.
Answer:
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Assessment 4
Science as Inquiry
Radiation, I
Item:
In 1909 Henri Becquerel left his sample of Uranium with some photographic paper. The Uranium was
found to have taken its own picture, in the darkness of the drawer where it was left. From this event and
the observations of the cloud chamber, indicate the proof that something from the Uranium caused the
film to change.
Answer:
The tracks in the cloud chamber were proof that something, although not directly seen was present
due to the tracks left. The photo film also showed that something was present because normally light is
needed to “expose” photographic film.
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Assessment 5
Science as Inquiry
Bean Counters
Item:
C14 is often used to tell the age of formerly living things. C14 has a half-life of about 10,000 years.
Now, a cave is discovered with the remains of burned wood from a fire. The wood was found to be
approximately 50,000 years old. What percent of the original radioactive C14 remains in the charred
wood? For full credit you must indicate the steps of how and why you solved the problem with the
methods you used.
Answer:
3.125% or 1⁄32 × 100%
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Assessment 6
Science as Inquiry
Eating the Difference
Item:
U238 is a potentially dangerous radioactive element produced for use in nuclear reactors. This element
has a half-life of approximately 1,000,000,000 years. If it were to be stored, how long would 1,000 kg
need to be stored in order to reduce its radioactive part to less than 10 kg? Be sure to indicate why you
used the method you did to solve the problem.
Answer:
7 half-lives or 7 billion years
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Assessment 7
Science as Inquiry
Radioactive Controls
Item:
Radioactivity can be detected with use of a Geiger counter—or its presence noted in a cloud chamber.
Radioactive substances’ radioactivity are also controlled by their half-life. If this is true, then what is the
best statement below?
A. The material will stop radiating when it is frozen.
B. The radiation will continue until no matter remains.
C. The matter changes into new substances over a specific amount of time.
D. The time of changing due to radiation depends on what is mixed with the material.
Justification:
Why did you pick your answer? Give good reasons and use drawings as well as explanations to give
proof.
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Assessment 8
Science as Inquiry
Radiation, II
Item:
Iodine131 is a radioactive isotope used in treating abnormal conditions of the thyroid gland in people.
The radiation from the decay of the isotope kills hyperactive cells in the thyroid. A normal thyroid gland
uses iodine as a basis for the production of a very necessary hormone called thyroxine. Iodine seems to
have very little other function in the human body.
Based on this information, why do you think the use of the radioactive iodine is so successful in
treating abnormal thyroid conditions?
Answer.
The iodine is extracted by the thyroid for use in making the hormone. Thus it is highly concentrated
in the gland and doesn’t concentrate anywhere else. This means only thyroid cells are damaged by the
emitted radiation, but not other body cells. This discrimination is highly desirable when using radiation
to kill cells.
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Assessment 9
Science as Inquiry
Age Correlations, I
Item:
Uranium 238 decay, rather than carbon14 decay, is used to date the age of the Earth because uranium238 :
A. Was more abundant than carbon when the earth was formed.
B. Has a longer half-life.
C. Decays at a more constant rate.
D. Is much easier to measure.
Justification:
What is measured when a radioactive substance such as U238 is used in determining the age of a rock?
Answer:
B. C14 has too short a half-life (5730 years) to be useful for billion-year lifetimes needed for the age
of the earth.
Justification answer should include some idea that it is the amount of daughter product formed that is
used to establish how much decay has occurred.
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Assessment 10
Science as Inquiry
Age Correlations, II
Item:
When early humans lived is determined by measuring when the rocks in which their skeletons are
found were formed. Why can the skeletons themselves not be “dated”?
A. Bones contain no carbon to use the carbon14 method.
B. Carbon14 has too short a half-life, so it has all decayed from the bones.
C. The materials in rocks follow physical laws more accurately.
D. There are more rocks available than there are bones, so the measurement is easier.
Justification:
Explain what limits the time period over which a radioactive dating method can be used.
Answer:
B. C14 has too short a half-life (5730 years) to be useful for million-year lifetimes needed for the age
of the early humans found.
Justification answer should include some idea that it is the amount of daughter product formed
relative to the parent present that is used to establish how much time has elapsed. When either of these
(too short, or too long) is too small to be measured, then the method is not useful.
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