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- Copy of Half-life SE biology
Developmental Biology (BIO 324)
College of Staten Island CUNY
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Name: Andrew Date: 2/6/
Student Exploration: Half-life
Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes.
Vocabulary: daughter atom, decay, Geiger counter, half-life, isotope, neutron, radiation, radioactive, radiometric dating
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
- Have you ever made microwave popcorn? If so, what do you hear while the popcorn is in the microwave?
popping
- If you turn the microwave on for two minutes, is the rate of popping always the same, or does it change? Explain.
changes
Gizmo Warm-up Like an unpopped kernel in the microwave, a radioactive atom can change at any time. Radioactive atoms change by emitting radiation in the form of tiny particles and/or energy. This process, called decay , causes the radioactive atom to change into a stable daughter atom.
The Half-life Gizmo allows you to observe and measure the decay of a radioactive substance. Be sure the sound is turned on and click Play ( ).
- What do you see and hear? There is popping at different rates and locations
Note: The clicking sound you hear comes from a Geiger counter , an instrument that detects the particles and energy emitted by decaying radioactive atoms.
What remains at the end of the decay process? only daughter atoms
Is the rate of decay fastest at the beginning, middle, or end of the process?
beginning
Activity A:
Decay curves
Get the Gizmo ready:
● Click Reset ( ). Be sure that User chooses half-life and Random decay are selected. ● Check that the Half-life is 20 seconds and the Number of atoms is 128.
Question: How do we measure the rate of radioactive decay?
Observe: Select the BAR CHART on the right side of the Gizmo and click Play.
What happens to the numbers of radioactive and daughter atoms as the simulation proceeds?
radioactive decreases and daughter increases
- Do the numbers of radioactive and daughter atoms change at the same rate throughout the simulation? Explain.
No, it gets slower
Experiment: Click Reset , and select the GRAPH tab. Run a simulation with the Half-life set to 5 seconds and another simulation with the Half-life set to 35 seconds. ✏ Sketch each resulting decay curve graph in the spaces below.
Interpret: How does the Half-life setting affect how quickly the simulated substance decays?
When its at 5 seconds it goes faster
- Collect data: Click Reset. Change the Half-life to 10 seconds and click Play. Select the TABLE tab and record the number of radioactive atoms at each given time below.
0 s: 128 10 s: 55 20 s: 28 30 s: 11 40 s: 6 50 s: 3
Activity B:
Measuring half-life
Get the Gizmo ready: ● Click Reset. ● Select Isotope A from the left drop-down menu. ● Check that Theoretical decay is selected.
Introduction: Different isotopes of the same element have the same number of protons but different numbers of neutrons in the nucleus. Some isotopes are radioactive.
Question: How do we find the half-life of a radioactive isotope?
- Observe: Select the GRAPH tab, and click Play. Based on the graph, what is your estimate of the half-life of isotope A?
15
- Measure: Turn on the Half-life probe. Use the probe to measure how long it takes for exactly one-half of the original radioactive atoms to decay.
What is the exact half-life of isotope A?
31
- Collect data: In the first row of the table below, write how many seconds represent one half-life, two half-lives, and so forth. On the next row, predict the number of radioactive atoms that will be present at each time. Then use the probe to find the actual values.
Half-life 0 1 2 3 4 5
Time (seconds) 0 31 62 94 125 155
Predicted # radioactive atoms 12864321684 Actual # radioactive atoms
128 64 32 16 8 4
- Calculate: Calculate the percentage of radioactive atoms that are left after each half-life.
Half-life 0 1 2 3 4 5
Percentage radioactive atoms 1005025 12 6 3.
- Apply: Suppose you found a material in which 12% of the original radioactive atoms were present. If the half-life is 47 years, how old is the material?
196 yers old
- Apply: Use the Gizmo to find the half-life of Isotope B. What is it?
17
- Practice: Click Reset. Select the Mystery half-life from the left menu. In this setting, the half-life will be different each time you run the simulation. Run at least three experiments. In each experiment, measure the half-life using the Half-life probe on the graph. (The half-life will be different each time.)
When you have found the half-life, click the camera (📷) icon. Right-click the image, and click Copy. Then paste the image below, and label each image with the half-life.
å
Explore: Use the Gizmo to explore whether the numberof atoms present affects the half-life that you measure. Describe your findings below:
Extend your thinking: The slow decay of radioactive materials can be used to find the age of rocks, fossils, and archaeological artifacts. In a process called radiometric dating , scientists measure the proportions of radioactive atoms and daughter atoms in an object to determine its age. Carbon-14 is a useful isotope because it is found in wood, ash, bone, and any other organic materials.
You can use the Half-life Gizmo to model the decay of Carbon-14, which has a half-life of approximately 6,000 years (actual value is 5,730 years). In the Gizmo, select User chooses half-life and Theoretical decay. Set the Half-life to 6 seconds (to represent 6,000 years) and the Number of atoms to 100.
Use the Gizmo to estimate the age of each of the objects below. For these questions, each second in the Gizmo represents 1,000 years.
Description Age (years)
Egyptian papyrus with 63% of its original carbon-14 atoms
Aboriginal charcoal with 22% of its original carbon-14 atoms.
Mayan headdress with 79% of its original carbon-14 atoms
Neanderthal skull with 3% of its original carbon-14 atoms
- Copy of Half-life SE biology
Course: Developmental Biology (BIO 324)
University: College of Staten Island CUNY
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