Name:_________________________________Date:_____________________Period:_____
Graphing Nuclear Decay
Worksheet
Directions
Cesium-137 is a radioactive isotope which is produced in fission reactions. It emits beta
particles to decay into barium-137. The half-life for this decay is approximately 30 years. You
are given a 128 gram sample of cesium-137 which you analyze every 30 years for 180 years.
Using this information, complete the table below (assume the atomic mass of cesium-137 and
barium-137 are identical), plot the data, and answer the following questions:
Grams of Cesium-137
128 grams
Grams of Barium-137
0 grams
Grams of Cesium-137
Remaining
Time
0 years
30 years
60 years
90 years
120 years
150 years
180 years
Time in years
Questions
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© 2004 High School Technology Initiative (HSTI) Educational Materials: The ATOM: Nuclear
Name:_________________________________Date:_____________________Period:_____
1. How long will it take for all of the cesium-137 to decay into barium-137?
______________________________________________________________________________
______________________________________________________________________________
2. Using your graph, how many years will it take for only 75 grams of cesium-137 to be
remaining?
______________________________________________________________________________
______________________________________________________________________________
3. After 10 half-lives, the radioactivity of an isotope is considered negligible. How many years
will it take for the sample of cesium-137 to reach this point?
______________________________________________________________________________
______________________________________________________________________________
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© 2004 High School Technology Initiative (HSTI) Educational Materials: The ATOM: Nuclear