Half-life of ¹³⁷Ba by Beta Emission
Obj: Determine T_½ of a radionuclide using a Geiger counter.

Materials: Geiger counter, Apple II computer, ¹³⁷Cs source (IsoGenerator)
Methods and Analysis
1.  Determine the background radiation for 15 second intervals using the Geiger-Mueller tube.
2.  Extract ¹³⁷Ba^* from the ¹³⁷Cs source following the methods described and place the elution onto a planchet.
3.  Record the count every 15 seconds on the computer for approximately 6-8 minutes.
4.  Subtract the background count from each value if significant (>5% of total counts)
5.  Graph the disintegration counts vs time.  Draw a smooth curved best-fit line.
6.  Determine on the graph where the number of counts is 2 the original counts, then estimate the half life.  Compare with the known T₂ of ¹³⁷Ba* and calculate a % error.
7.  Write the entire nuclear decay of ¹³⁷Cs to ¹³⁷Ba by beta and gamma photon emission.
8.  Which nucleus is more stable, ¹³⁷Ba* or ¹³⁷Ba.  Explain your answer.

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