2009 Advanced Laboratories Conference Abstract Detail Page

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Abstract Title: Determining the half-life of 40K from the activity of salt substitute
Abstract: Typical half-life experiments in student laboratories involve directly measuring rate vs. time for an isotope that decays on a time scale amenable to laboratory measurement.  For example, in the Modern Physics course at Wittenberg University, students use a 2" NaI(Tl) detector and a multichannel scaler to obtain rate vs time data for isotopes such as 137mBa (obtained from a commercial mini-generator kit) or 56Mn (produced by neutron activation of manganese dioxide). We have recently supplemented these experiences with an experiment making use of a different method of measuring a half-life, in which students determine the half-life of 40K using a container of salt substitute (mostly KCl). Students use the NaI(Tl) detector to obtain the photopeak rate with and without the salt substitute present, determine the background-subtracted rate, and then apply standard correction factors for the photopeak efficiency of the detector to obtain the activity of the sample. Since the mass and chemical composition of the sample and the natural abundance of 40K are known, the decay constant can be obtained from the measured activity. This experiment complements the direct half-life measurements in technique and in conceptual content, and gives students experience with a standard method for measuring very long half-lives.
Abstract Type: Poster
Contributed Poster: Download the Contributed Poster
Session: Session IX - Effective Experiments Poster Session

Author/Organizer Information

Primary Contact: Elizabeth A George
Wittenberg University
Physics Dept
PO Box 720
Springfield, OH 45501
Phone: 937-327-7854
and Co-Presenter(s)
Paul A Voytas, Wittenberg Univ., pvoytas -at- wittenberg.edu