Teacher’s Notes

Teacher’s Notes
Purpose:
The purpose of this activity is to help students discover, through a model,
how scientists determine the age of a rock sample by way of radioactive
decay. It is important to discuss with the students the use of models in
science with its pitfalls and the advantages. This activity also incorporates
several reading comprehension strategies throughout the lesson.
Science Benchmarks:
SC.7.N.3.2 Identify the benefits and limitations of the use of scientific models.
SC.8.N.3.1 Select models useful in relating the results of their own investigations.
SC.6.N.1.4 Discuss, compare, and negotiate methods used, results obtained, and explanations among groups of
students conducting the same investigation.
SC.7.N.1.4 Identify test variables (independent variables and outcome variables (dependent variables) in an
experiment.
SC.7.E.6.3 Identify current methods for measuring the age of Earth and its parts, including the law of
superposition and radioactive dating.
Science Process Skills:
Inferring
Identifying variables
Organizing and analyzing data
Observing/measuring/graphing
Interpreting and communicating results
Using a model to communicate
Reading Standards:
The student uses multiple strategies to develop grade appropriate vocabulary.
Use new vocabulary that is taught directly.
Listen to, read and discuss conceptually challenging words.
The student uses a variety of strategies to comprehend grade level text.
use background knowledge of subject and related content areas, prereading
strategies, graphic representations, and knowledge of text structure to make
and confirm complex predictions of content, purpose, and organization of a
reading selection;
use strategies to repair comprehension of grade-appropriate text when selfmonitoring indicates confusion, including but not limited to rereading,
checking context clues, predicting, note-making, summarizing, using graphic
and semantic organizers, questioning, and clarifying by checking other
sources.
Anticipation Guide
Directions: Go back through your notes and review what we have done on
radioactivity. Then, read each statement below. If you believe that a statement is
true, place a check in the Agree column. If you believe the statement is false,
place a check in the Disagree column. Be ready to explain your choices. You will
repeat the activity after we do the lab.
Agree
Disagree
Agree
Radiation is the energy or product
given off from an unstable nucleus.
A half-life is the time it takes
for ½ of an unstable substance to
break down.
In living matter radiation damages
cells that can lead to serious
burns and death.
The length of an element’s halflife depends on how much of it you
have.
Gamma rays have a short half-life
and can pass easily through paper
and the human body.
If 80 grams of a substance has a
half-life of 8 days, after the
first half-life there would be 10
grams remaining.
Radioactivity does not transform
matter.
Disagree
Grade 8
Chapter 13, Section 1
Pg 380-386
What is
radioactivity?
What are the kinds
of radioactive
decay?
1.
2.
a.
b.
3.
What is an isotope?
What are the
effects of radiation
on matter?
1. living
2. non-living
What is a half-life?
How do we use
radiation?
Summary:
Name:________________________________
Period: ________
Lab- Candium Detected in Sample from Mars
Introduction:
Candium, a radioactive substance, has been accidentally
brought back to Earth by a recent mission to Mars. It was
found in a contaminated sample of rock. NASA believes that
the only thing that can be done is send a sample of the
substance to the most educated experts on radioactive decay
and half lives. (Which is YOU). You have been assigned to
the following task. You must study Candium decay and report
back to headquarters within one day with a report that
details the decay of Candium and the possible effects Candium
will have on Earth and its inhabitants.
What is the question you are trying to answer?
_____________________________________________________________________________
_____________________________________________________________________________
Assignment:
Complete the following procedure to discover more about the half-life
of Candium. As stated before, this is only for the most educated experts. DO
NOT EAT THE CANDIUM (Mm) BEFORE YOUR DATA IS REVIEWED AND CHECKED BY THE
LABORATORY ADMINISTRATOR! Remember, only a limited amount of Candium atoms
available to the planet. Following is a procedure to conduct the experiment
for NASA:
Materials:
100 Atoms Candium (Skittles)
2 Cups
Graph Paper
Foil
Procedure:
1. Obtain cup with 100 atoms of Candium.
2. Cover the cup and gently shake for 10 seconds (the pre-determined
half-life of Candium is 10 seconds).
3. Gently pour out Candium on to the high-tech receptacle.
4. Count the number of atoms with the “S” decay marker side facing up—
and record the data. These atoms have “decayed”, however there is no
gamma radiation so your skin will not turn green and you will not
become angry.
5. Return only the pieces not showing the “S” marker to the cup.
6. Store the “decayed” atoms in decay receptacle.
7. Gently shake the cup for 10 seconds and repeat steps 3-6.
8. Continue shaking, counting, and storing until all the atoms have
decayed.
9. Graph the number of undecayed atoms vs. time on a separate graph
paper.
10.Repeat this procedure with 80 atoms.
Remember a half-life is similar to a trial run in an experiment. To find the
decayed atoms, use the half-life number (trial run).
100 Atom Data:
Half Life
Initial
1
2
3
4
5
6
7
8
9
10
# Undecayed Atoms
Total Time (sec)
80 Atom Data:
Half Life
Initial
1
2
3
4
5
6
7
8
9
10
# Undecayed Atoms
Total Time (sec)
1. Graph the half-life verses the number of undecayed atoms. Use different
colors for each trial (100atoms and 80 atoms)
Do the following on a separate sheet of paper:
2. At the end of 2 half-lives, what fraction of Candium had not decayed?
_____________________________________________________________________________
After 5 half-lives and 9 half-lives, what fraction of Candium had not
decayed? Show your work.
_____________________________________________________________________________
3. We used a model of radioactive decay. What did the candy represent?
_____________________________________________________________________________
What represented the radioactive decay in the model?
_____________________________________________________________________________
What was the limitation of this model?
_____________________________________________________________________________
4.List the variables that affected your results.
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
Communicate Your Results
Use the following words to complete the sentences below. Use the completed
sentences to write your conclusion. In order for your paragraph to make
sense, the sentences must be in correct order.
radioactive decay
half
atoms
decayed atoms
model
cup
pieces
process
repeated
simulates
1. The results show that approximately ____________ of the total amount of
the element decayed within the first half-life.
2. The experiment began by using 100 candy pieces to represent __________.
3. The purpose of this activity was to use a __________ to demonstrate
radioactive decay of certain elements.
4. Scientists can use __________ __________ of elements to determine the age
of rocks.
5. All the pieces with the “S” facing up represented __________ __________
and were removed.
6. This __________ continued for 10 half-lives.
7. The candy pieces were placed in a __________ and were shaken for 10
seconds.
8. The experiment was __________ using 80 “atoms”.
9. The __________ were dropped into a tray.
10. The __________ __________ were counted and recorded.
11. This __________ radioactive decay of real atoms.
Conclusion answer key
The purpose of the activity was to use a model to demonstrate
radioactive decay of certain elements. Scientists can use radioactive decay
of elements to determine the age of rocks.
The experiment began by using 100 candy pieces to represent atoms. The
candy pieces were placed in a cup and were dropped into a tray. All the
pieces with the “S” facing up represented decayed atoms and were removed. The
undecayed atoms were counted and recorded. This process continued for 10 half
lives. The experiment was repeated using 80 “atoms”.
The results show that approximately half of the total amount of the
element decayed within the first half-life. This simulates radioactive decay
of real atoms.
Dear Scientist,
I am a teacher at Sligh Middle School in Tampa, Fl. My students have been
working with samples of canedeum and I have been very concerned about the
safety of the substance. Please send me a letter that outlines your findings
complete with pictures and diagrams. We are most interested in the possible
effects that canedeum will have on the Earth’s atmosphere and the living
creatures here.
Thank you so much for all of your help!