Lab 1.3 – Carbon-14 Half-life and Radioactive Dating
Background: The nuclei of unstable atoms disintegrate by decay spontaneously, emitting alpha or beta particles and gamma radiation. Types of atoms that undergo this process are called radioactive isotopes. A decaying isotope is referred to as a parent atom and the atom produced is a daughter atom.
In this activity, simulates will be used to represent atoms of carbon-14, a common radioisotope produced in the upper atmosphere and consumed by living creatures. Its radioactive properties make it ideal for use in estimating age.
Simulates + C-14
· The black side of the simulate will represent individual parent atoms of carbon-14,
· The white side will represent the daughter atoms of the decay.
PURPOSE of Activity: To MODEL the decay characteristics of carbon-14 and determine the age of materials from the amount of the model carbon-14 remaining.Question: Can radioactive simulates be used to model C-14 decay and therefore be used to estimate the age of a fossil?
Equipment: One set of 200 simulates, one shaker, graph paper
Procedure:
1. Write your Hypothesis/Claim for this lab
2. Place the entire set of 200 simulates in the shaker. Place hand over the open end and mix contents. Four really good shakes should do it.
3. Carefully toss or spill the entire contents of the shakers on a flat surface in front of you.
· Carefully separate out all of the simulates that are white side up. [ Remember, these are the daughter atoms of carbon-14 that have decayed]
· Count the number of black simulates and record this number in Table 1.
4. Place only the black simulates in the shaker
5. Repeat procedure #2 until all of the stimulates are moved to one side.
· Record the number of black simulates remaining each time and in Table 1.
6. Convert the number of simulates for each toss into a percentage.
# of black simulates in toss
200 (total of simulates) X 100 = ______%
7. On a graph paper, plot the toss number (x-axis) against the percentage of carbon-14 remaining (y-axis).
8. Use the graph and your knowledge of the half-life of carbon-14, to estimate the age of each of the fossils in the analysis section of the lab.
9. Answer all of the questions below, in your analysis and conclusion section.
10. Develop the next logical question to investigate
11. Work with your partner to construct your posters for peer review
Data/Evidence: Include Table and Graph
Table 1
Toss # = Half-life(1 = 5730 years) / Carbon-14
(black side of simulate) / Percentage of
Carbon-14
0 / 200 / 100%
1
2
3
4
5
6
7
8
9
10
Analysis and Conclusion:
1. Does exactly the same fraction of carbon-14 decay during each half-life? What does this suggest about half-life? Why are such variations not likely to be obvious when actual atoms are involved?
2. Use your graph to determine the age of the following based on the amount of carbon-14 remaining.
a. A mammoth frozen in a glacier that has only one eighth (12.5%) of the original carbon-14.
b. The charcoal burned in a primitive man’s campfire that has only 20% of the original carbon-14.
c. The bee pollen found in a piece of amber. Assume that only one eighth (3.4%) of the original carbon-14 remains in the pollen.
3. Can carbon-14 decay be used to date items from Precambrian times (60,000,000 years ago)? Why or why not?
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