Soil analysis using a 2″ NaI gamma detector

Abstract

We describe an undergraduate physics laboratory experiment that uses a 2-inch diameter NaI gamma detector to measure natural radiation in soils. Students first calibrate the detector for the source-detector geometry, energy-dependent detection efficiency, and sample self-absorption. Then, the activity of the 238U and 232Th decay series, as well as the activity of 40K in the soil, are measured. The results are comparable in accuracy to those obtained using a high-resolution germanium gamma detector.

Low budget gamma spectroscopy

“…The KCl sample provides a peak at 1461 keV, and the Fiestaware a peak at 186 keV. To determine the peak center and area, we use the Gaussian peak fitting method described in references [1,6]. In figure 3 we plot these eight energies as a function of bin number.…”

“…To calculate the energy dependence of the detector's efficiency, we use the methods of references [1,7]. For a gamma of energy E, the count rate C is related to the yield Y (given in table 1) and the activity A through the empirical formula [8,9]…”

“…Gamma spectroscopy experiments are a valuable exercise in undergraduate physics and engineering laboratories [1][2][3]. They offer students the opportunity to learn about detector calibration and to perform measurements of environmental gamma radiation, and they illustrate and supplement material on nuclear physics covered in the classroom.…”

“…The methods of calibration and analysis we use are similar to those of reference [1], where the radioactive sources used for both energy and efficiency calibration do require licensing. In contrast, in our experiments presented here, energy and efficiency calibration is performed with sources whose activity is low enough that no restrictions apply in acquiring them, and no licensing is required.…”

“…In contrast, in our experiments presented here, energy and efficiency calibration is performed with sources whose activity is low enough that no restrictions apply in acquiring them, and no licensing is required. In addition, shielding of the background radiation in reference [1] was provided by lead bricks, which are common in radiation laboratories, but not usually available in the general student lab. As lead bricks are expensive, not easy to obtain, and difficult to deal with, we devised an experimental method without lead shielding.…”