PURPOSE: Measure the half-life of Ba 137, approximately 156 seconds.

DESCRIPTION: The 660 keV gamma ray from a Cesium 137 source is actually from its beta decay daughter, Barium 137. The cesium decays into a metastable state of barium with a half-life of about 156 seconds. Using a chemical technique the barium is separated out from the sample of radioactive powdered cesium. The 660 keV gamma rays from the decaying barium daughter are detected by a Geiger tube and a graph of counts versus time plotted for equal time intervals using a Macintosh computer with the Universal Lab Interface and the radioactivity and graph plotting software.

SUGGESTIONS: Think about this one before you do it and get instruction on operation of the system.

REFERENCES: (PIRA 7D10.20) See Demonstration Reference File for further information about the ULI and the nuclear physics involved.

EQUIPMENT: Macintosh IIci computer with Universal Laboratory Interface, radioactivity detector, and radioactivity and graph plotting software, with cesium/barium minigenerator.

SETUP TIME: 1 hour.

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