Half-Lives Activity

Before you start answer the following, when finished check with your teacher and you will receive supplies.

1)  What is isotope dating (carbon dating) used for?

2)  If you toss 100 pennies in the air, when they land, how many heads would you expect to see on average?

3)  Do you know in advance which will land as heads and which will land as tails?

When you receive your materials:

1)  Count to be sure you have 100 pennies to start with.

2)  Give the pennies a good shake then toss them (gently try not to drop any) on the table

3)  Remove all pennies that are tails up.

4)  Count remaining pennies and enter this data on your data table

5)  Repeat 2-4 until you have no pennies left

Data Table:

Toss 1
Toss 2
Toss 3
Toss 4
Toss 5
Toss 6

Note there are 6 tosses here, if it takes more please continue the table.

When you are finished return to your seats, send one member of your group to report your data to the front.

Now use a ruler to draw a neat line graph of your data in the space below. Put the tosses on the x axis and the amount of pennies on the y axis and don’t forget to label your axis and graph

Now copy the completed data table from the board and average the results:

Now make a line graph of the average data:

Science Questions:

1. How many shakes did it take you to get rid of all of your pennies? How did this compare to the other groups?

2. Whyshould you average your data with the data from other groups?

3. Sodium-24 (Na-24) has a half life of 15 hours. Fill in the following table showing the decay of a 100g sample.

grams of Na -24 / hours passed
100 / 0
50 / 15
30
12.5
6.25
75

4. Graph your data table from #3.

5. How does this graph compare to the graph for your pennies?

6. Using your graph approximate how many hours have passed if you have 75 grams of your original sample of Na-24 left.

7. If 40 hours have passed how much of the original 100 gram sample should be left?

8. Carbon 14 has a half life of 5770 years. If you start out with 100 grams of carbon 14 in how many years will you only have 25 grams left?

9. In what way is the penny toss like the decay of a radioactive element?