7Be measurements in agricultural soil using a low resolution NaI(Tl) detector

Abstract

⁷Be is a cosmogenic radionuclide used in gamma-ray spectrometry to trace short-term sediment movements, such as soil mobilization. Gamma-ray detectors with low resolution cannot distinguish photons with similar energies, making it challenging to detect ⁷Be using these instruments. When ⁷Be decays, it emits gamma rays with an energy of 477 keV, similar to those of other radioisotopes (²²⁸Ac, 462 keV; ²⁰⁸Tl, 511 keV) and of the annihilation effect (511 keV). For this reason, high-resolution detectors, such as HPGe, are typically used, as they can differentiate photons and distinguish the mentioned radionuclides which emit similar energies. However, unlike low-resolution detectors, HPGe detectors are much more expensive than other gamma detectors, both in purchase and maintenance costs. These constraints make the widespread use of ⁷Be measurements for soil erosion studies impractical on a global scale. In this study, we propose a method for analyzing ⁷Be using a low-resolution scintillation detector, specifically a NaI(Tl) detector. The method eliminates the influences on the ⁷Be energy window using reference from other spectral regions. The approach was applied to evaluate soil mobilization in two agricultural plots, one with terraces and the other without terraces. The results of ⁷Be were supported by the measurement of its half-life. Most of the ⁷Be activity in agricultural soil samples was above the minimum detectable activity, allowing an assessment of the spatial distribution of erosion and deposition rates across the landscape. Soil redistribution was quantitatively evaluated, indicating that terraced soil experiences less erosion than nonterraced soil.