Rapid Screening for Uranium in Soils Using Field-Portable X-ray Fluorescence Spectrometer: A Comparative Study

Abstract

Depleted uranium (DU) armor-penetrating munitions are used on testing and training ranges leading to elevated concentrations of U in range soils. To prevent exposure from secure areas contaminated with DU hotspots, easy and rapid screening methods are needed. This study explores the feasibility of field-portable X-ray fluorescence (FPXRF) spectrometry as a fast screening tool for locating hotspots of DU in the field. Direct comparisons of results were made for U concentrations in the soil obtained using FPXRF spectrometry and measurement of U using inductively coupled plasma mass spectrometry (ICP–MS) after acid digestion. The environmental samples included both field-range contaminated soils collected at a munition testing facility and soils spiked with uranium dioxide, uranium trioxide, and uranyl nitrate. Using U concentrations measured with ICP–MS from split samples, FPXRF operating procedures and conditions such as analysis time, soil moisture content, sample amount, and sample packing factors were optimized. Results showed that the FPXRF technique yielded similar U concentrations as ICP–MS measurements after acid digestion in both standard soil (NIST) samples and DU-contaminated range soils. In field-contaminated soils, U values with FPXRF were 88.8% of the measurements with ICP–MS with a significant correlation (R2: 0.98, n = 8). Sample preparation affected the uranium concentration measurements made with FPXRF in the laboratory and in the field. A loose packing of the samples in the sample containers, higher sample occupancy, and low soil moisture yielded significantly higher U concentrations by 4–5, 15–50, and 43%, respectively. The measured soil U concentrations were not affected by the variation of the sample analysis time. This study suggests that FPXRF is a promising fast screening tool for field DU hotspots as well as detection/location of penetrators in the fields that can increase the ability to rapidly and inexpensively manage DU on ranges and help ensure sustainable use of DU munitions on testing and training ranges.