The Caliper

Nuclear Radiation with Computers and Calculators

By John Gastineau

Nuclear Radiation with Computers and Calculators, which was introduced earlier this year, includes some exciting new experiments for physics, chemistry, and physical science teachers. Each of the six experiments has a computer version (for LabPro or ULI) and a calculator version (for LabPro or CBL 2). The Nuclear Radiation CD included with the book contains the word processing files for the six student experiments:

• Alpha, Beta, and Gamma
• Distance and Radiation
• Lifetime Measurement
• Counting Statistics
• Background Radiation Sources
• Radiation Shielding

In each of these experiments, you can use either the Vernier Radiation Monitor or the Student Radiation Monitor.

The six experiments cover a broad spectrum of topics in high school and college nuclear radiation curriculum. One of our favorites is Lifetime Measurement. In this experiment, students use a source called an isogenerator that contains cesium-137, which decays to an isotope with a short half-life, barium-137. Using a simple chemical separation process, the isogenerator allows you to easily remove a sample of barium with a half-life of 2.552 minutes by gamma emission, making this system an ideal one for classroom study. A 30-minute experimental run covers almost 12 half-lives, so the observed activity drops to about 0.3% of the initial value. The cesium-137 source in the isogenerator will last for years and can be reused many times.

Shown here are some sample data from this experiment. Notice that the exponential curve fit done on the first 15 minutes of data yields a decay constant equal to 0.277 min -1 (the value of C in the curve fit). Using the formula t1/2 = ln 2 / ë , the half-life, t1/2, is found to be 2.50 minutes for these data. The final five minutes of data can be used to determine the background count rate from the combination of cosmic rays and leaked cesium. (With time, isogenerators will sometimes leak small amounts of the cesium-137 isotope.) The calculator data below show an exponential fit done after background levels are subtracted from the data. The decay rate value of 0.00444 s -1 yields a half-life value of 156 seconds, or 2.60 minutes.

Nuclear Radiation with Computers and Calculators
Order Code NRCC	$25
Student Radiation Monitor (detects β and γ only)
Order Code SRM-BTD	$145
Radiation Monitor (detects α, β and γ)
Order Code RM-BTD	$205