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Natural Science - Year II

Unit 53 Lab: Determining Half-Lives

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Unit 53 Lab: Electromagnetic Radiation


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Unit 53 Laboratory Activity: Half-Lives

Goal: To demonstrate the principle of half-lives using pennies

Materials:

Procedure:

  1. Put all the pennies in the box, tails up.
  2. Shake the box throughly.
  3. Remove all the pennies that are now heads up. These represent pennies that have decayed during one half-life. Set them aside. Put the tails-up pennies back in the box, keeping them tails up.
  4. Record the number of heads-up pennies, and the step.
  5. Repeat steps 2-3 until all the pennies are removed from the box. For each trial, record the total number of heads-up pennies removed, and the trial step.

Data Analysis

  1. On graph paper, plot the trial number along the horizontal axis (1, 2, 3,.....last trial).
  2. On the vertical axis, plot the total number of "decayed pennies" removed as of that step above each trial with a SQUARE. For example, if you removed 37 pennies in trial 1 and 22 pennies in trial 2, the square above the number 2 should be at 59 pennies.
  3. Plot the number of "undecayed pennies" for that step with a circle.

Report

  1. Describe your materials and procedure in sufficient detail that another student could complete the lab to test your results.
  2. Include your data in a table, and your graph.
  3. Are the "decayed" function and "undecayed" function lines straight lines or curves? What does this indicate about predicting decay rates for large numbers of "penny atoms" after 2, 3, or 4 half-lives?