Get a half-life. (Hands-on Activity and Math Skills).
1,000 pennies * container large enough to hold the pennies * graph paper * pencil * ruler
1. Find a large, flat surface, such as a large table or floor.
2. Randomly toss the pennies onto the surface.
3. Remove all pennies that land tail-side up--representing decayed atoms--and place them in a pile away from your work surface.
4. Collect all the remaining pennies and toss again. Remove the decayed atoms and place in a second pile.
5. Repeat the experiment until all the pennies have been removed; start a new pile after each toss.
6. Construct a data table. Count up each pile of pennies to record the number of decayed and undecayed atoms for each half-life.
7. Use your data to create a line graph. On the x-axis, plot the number of half-lives, and on the y-axis, undecayed atoms.
The chance that any penny will come up tails is always 50 percent.
Approximately half the pennies remain after the first toss, about 1/4 after the second, and then 1/8, 1/16, etc. When a quantity decreases by a fixed fraction--here 1/2--it's known as exponential decay. The time it takes for 1/2 the pennies to be removed is called the half-life. This is analogous to the time it takes for a radioactive substance to lose half its radioactivity.
1. Gold-198 has a half-life of 2.69 days. If you start with 200 grams, how much remains after 10.76 days?
2. Iodine-131 has a half-life of 8.1 days. There are 5 grams left after 32.4 days. How many grams were there to begin with?
3. If a 100-gram sample of nitrogen-16 decays to 12.5 grams in 21.39 seconds, what is its half-life?
1. 12.5 grams 2. 80 grams 3. 7.13 seconds
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|Date:||Dec 13, 2002|
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