Experiment
9.1
Understanding Half-Life
Prelab = 12 Lab Report = 98
Introduction:
grams of carbon-14 today, in 5730 years you would have In any sample of a radioactive isotope, the individual
50 grams of the carbon-14 left. You would have 25 atoms are decaying in a random fashion. It is impossible
grams left after 5730 more years had passed. Half-lives to predict which atom is the next to decay, yet statistically
of radioactive isotopes vary greatly, from much less than you can predict how many atoms will decay in a certain
a second to billions of years. The half-life is a very period of time. Scientists measure how much time
important consideration when choosing a radioactive elapses while half of the atoms of a given radioactive
isotope for a specific application such as a medical sample decay. That time is called the half life. For
tracer. example, the half-life of the carbon-14 isotope is 5730
years. This means that if you were to start with 100
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Objectives:
1. Interpret a model of radioactivity and half-life. 3. Relate half-life and geologic dating. 2. Demonstrate the connection between half-life and a decay graph.
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Apparatus :
Shoe box or equivalent 200 or more pennies•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Procedure:
2. 1. Place at least 200 pennies on the counter tails up.
Then put them into a paper bag. Shake the bag for several seconds. Open the bad and pour the pennies onto the counter and remove all the pennies that have
3. the “heads” side up. Carefully count these pennies
and record the number on Data Table 1. Do not put
4. these pennies back in the box. Put the other pennies
back in the bag.
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Shake the bag again for several seconds. Open the bag and pour pennies onto the counter and again remove all the pennies with “heads” side up. Count the pennies and record in Data Table 1.
Continue this process until one or no pennies remain. Record the number each time.
Put all the materials away and begin the calculations and questions.
(12) Prelab Questions:
(2) 1. Explain what is meant by the term half-life. (2) 2. What is the half-life of carbon-14?
(2) 3. How can carbon-14 help determine the
age of a fossil?
4. Suppose you have a radioactive isotope with
a half-life of two years and you start with 800 grams of this substance today. (14) Data:
(2) a. How much will you have two years from
today?
(2) b How much will you have eight years from
today?
(2) 5. Is the quantity of a radioactive isotope
ever equal to exactly zero? Explain you answer.
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
How many pennies did you begin with? _____ Shake number Number of pennies removed
Experiment 9.2
December 18, 2009
Page 1
(10) Stamp of Approval..…..
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(12) Calculations : Using your data complete the table below.
(2) 1. In this exercise, what is the “half-life” of your “atomic pennies”? (You choose!)
(10) 2. Use this value to calculate “Time passed.”
Time passed Pennies remaining in bag
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(38) Analysis:
(2) 6. Is it possible to predict approximately how many (20) 1. Make a graph of your results using Graphical
pennies will be “heads” up for each shake? Explain Analysis. Plot time on the x-axis and pennies
your answer. remaining on the y-axis.
7. Check with at least two other groups in your class. (2) 2. How would you describe the shape of your graph?
Look at both the data collected and the graphs you (4) 3. Suppose you had started with 1000 pennies.
constructed. Would the shape of the graph be different? Explain
(2) a. Was your data identical to other groups? your answer.
(2) b. Was your graph identical to other groups? (2) 4. Approximately what percent of the pennies were
(2) c. Explain the similarities and differences. removed with each shake?
(2) 5. Is it possible to identify in advance which pennies
will be “heads” up?
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
(12) Real World Connections
(4) 1. The half-life of iodine-125 is 60 days. The half-life
of iodine-131 is 8.05 days. Often iodine is used to help identify diseases of the thyroid gland. Which of these two isotopes do you think would be the best to use in this application? Explain your answer. (4) 2. One of the controversies surrounding the use of
nuclear power is the storage of nuclear waste. Explain how the concept of half-life is an important consideration in this debate.
(4) 3. In a tree or other living organism, the amount of
carbon-14 is quite low. In fact, the number of decays or disintegrations is only about 15.3 disintegrations per minute. This rate remains constant while the tree is alive because the carbon-14 is being replaced in the tree through respiration. When the tree dies, the rate slowly decreases according to the half-life of carbon-14. Suppose a piece of fossil tree is
analyzed and found to be disintegrating at a rate of Experiment 9.2
about 3.8 disintegrations per minute. About how old is this fossil?
No Conclusion
December 18, 2009 Page 2
Experiment
9.1
Understanding Half-Life
Prelab = 12 Lab Report = 98
Introduction:
grams of carbon-14 today, in 5730 years you would have In any sample of a radioactive isotope, the individual
50 grams of the carbon-14 left. You would have 25 atoms are decaying in a random fashion. It is impossible
grams left after 5730 more years had passed. Half-lives to predict which atom is the next to decay, yet statistically
of radioactive isotopes vary greatly, from much less than you can predict how many atoms will decay in a certain
a second to billions of years. The half-life is a very period of time. Scientists measure how much time
important consideration when choosing a radioactive elapses while half of the atoms of a given radioactive
isotope for a specific application such as a medical sample decay. That time is called the half life. For
tracer. example, the half-life of the carbon-14 isotope is 5730
years. This means that if you were to start with 100
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Objectives:
1. Interpret a model of radioactivity and half-life. 3. Relate half-life and geologic dating. 2. Demonstrate the connection between half-life and a decay graph.
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Apparatus :
Shoe box or equivalent 200 or more pennies•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Procedure:
2. 1. Place at least 200 pennies on the counter tails up.
Then put them into a paper bag. Shake the bag for several seconds. Open the bad and pour the pennies onto the counter and remove all the pennies that have
3. the “heads” side up. Carefully count these pennies
and record the number on Data Table 1. Do not put
4. these pennies back in the box. Put the other pennies
back in the bag.
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Shake the bag again for several seconds. Open the bag and pour pennies onto the counter and again remove all the pennies with “heads” side up. Count the pennies and record in Data Table 1.
Continue this process until one or no pennies remain. Record the number each time.
Put all the materials away and begin the calculations and questions.
(12) Prelab Questions:
(2) 1. Explain what is meant by the term half-life. (2) 2. What is the half-life of carbon-14?
(2) 3. How can carbon-14 help determine the
age of a fossil?
4. Suppose you have a radioactive isotope with
a half-life of two years and you start with 800 grams of this substance today. (14) Data:
(2) a. How much will you have two years from
today?
(2) b How much will you have eight years from
today?
(2) 5. Is the quantity of a radioactive isotope
ever equal to exactly zero? Explain you answer.
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
How many pennies did you begin with? _____ Shake number Number of pennies removed
Experiment 9.2
December 18, 2009
Page 1
(10) Stamp of Approval..…..
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
(12) Calculations : Using your data complete the table below.
(2) 1. In this exercise, what is the “half-life” of your “atomic pennies”? (You choose!)
(10) 2. Use this value to calculate “Time passed.”
Time passed Pennies remaining in bag
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
(38) Analysis:
(2) 6. Is it possible to predict approximately how many (20) 1. Make a graph of your results using Graphical
pennies will be “heads” up for each shake? Explain Analysis. Plot time on the x-axis and pennies
your answer. remaining on the y-axis.
7. Check with at least two other groups in your class. (2) 2. How would you describe the shape of your graph?
Look at both the data collected and the graphs you (4) 3. Suppose you had started with 1000 pennies.
constructed. Would the shape of the graph be different? Explain
(2) a. Was your data identical to other groups? your answer.
(2) b. Was your graph identical to other groups? (2) 4. Approximately what percent of the pennies were
(2) c. Explain the similarities and differences. removed with each shake?
(2) 5. Is it possible to identify in advance which pennies
will be “heads” up?
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
(12) Real World Connections
(4) 1. The half-life of iodine-125 is 60 days. The half-life
of iodine-131 is 8.05 days. Often iodine is used to help identify diseases of the thyroid gland. Which of these two isotopes do you think would be the best to use in this application? Explain your answer. (4) 2. One of the controversies surrounding the use of
nuclear power is the storage of nuclear waste. Explain how the concept of half-life is an important consideration in this debate.
(4) 3. In a tree or other living organism, the amount of
carbon-14 is quite low. In fact, the number of decays or disintegrations is only about 15.3 disintegrations per minute. This rate remains constant while the tree is alive because the carbon-14 is being replaced in the tree through respiration. When the tree dies, the rate slowly decreases according to the half-life of carbon-14. Suppose a piece of fossil tree is
analyzed and found to be disintegrating at a rate of Experiment 9.2
about 3.8 disintegrations per minute. About how old is this fossil?
No Conclusion
December 18, 2009 Page 2