Alpha spectrometric analysis and environmental assessment of uranium concentrations in soil and vegetation from the Tafila District, Jordan

This study aims to determine the specific activity of natural uranium isotopes, including uranium-238 (²³⁸U), uranium-234 (²³⁴U), and uranium-235 (²³⁵U), in soil and vegetable samples - specifically tomato, potato, onion, carrot, and radish - collected from the Tafila district, Jordan, and to assess the soil-to-plant transfer factors using alpha spectrometry with a passivated implanted planar silicon (PIPS) detector. A total of eight soil samples and eight corresponding vegetable samples were obtained from eight distinct locations. The results revealed considerable spatial variability in uranium activity concentrations, reflecting the influence of geological formations and environmental conditions. The average activity concentrations were 251.6 ± 14.2 Bq/kg for ²³⁸U, 10.5 ± 1.9 Bq/kg for ²³⁵U, and 248.8 ± 13.9 Bq/kg for ²³⁴U in soil samples, while vegetable samples showed lower concentrations of 3.2 ± 0.16, 0.21 ± 0.05, and 3.1 ± 0.17 Bq/kg for ²³⁸U, ²³⁵U, and ²³⁴U, respectively. The calculated transfer factors ranged from 4.4 ± 0.4 × 10⁻³ to 29.1 ± 1.8 × 10⁻³ for ²³⁸U, 6.4 ± 1.4 × 10⁻³ to 33.0 ± 15.7 × 10⁻³ for ²³⁵U, and 4.3 ± 0.4 × 10⁻³ to 28.7 ± 1.9 × 10⁻³ for ²³⁴U, which reflects notable differences in uranium uptake efficiency among the studied plant species. A strong correlation (R² = 0.99) was observed between ²³⁸U and ²³⁴U in both soil and vegetable samples, suggesting isotopic equilibrium through natural decay. These findings provide essential baseline data for future studies on uranium mobility, bioavailability, and potential radiological risks in agricultural systems within the Tafila District.