Alternative Detector Methods for Upper-Division Physics-Laboratory Accuracy

Measuring naturally occurring radioactive material is of great interest in monitoring soil and rocks, which are important in assessing health risks to a population and serves as a reference in documenting changes to environmental radioactivity. These measurement practices are taught to upper division physics students in laboratory. Physics students study gamma spectroscopy and isotopes that produce decays using Ge detectors, whose operation require liquid nitrogen cooling and is therefore costly. The use of an affordable and more portable detector, the NaI detector, without sacrificing the precision needed in upper division physics courses is being studied. Known decay products from sources containing 40-K, 238-U, and 232-Th were used for calibration. The gamma energy peaks that were measured include: 1440 keV for K-40, 1764 keV for the Uranium-238, and 2614 keV for the Thorium-232 series. A secular equilibrium was used to assume that the activity of each isotope within their decay series were the same. The results from the calibration sources indicate using the NaI detector for monitoring soil samples is efficient, cost effective and promising.