## 3 Results
### Activity Ratios of Activity Concentration  
The activity ratio of \({}^{232}\)Th to \({}^{226}\)Ra can indicate the origin and stability of the nuclides within the \({}^{232}\)Th and \({}^{238}\)U decay series [9; 30; 42]. Furthermore, the activity ratios of \({}^{40}\)K/\({}^{232}\)Th and \({}^{40}\)K/\({}^{226}\)Ra can be used to evaluate the presence of heavy or light minerals in the sampling sites [9; 54].  
Figure 4a-c displays the activity ratios of \({}^{232}\)Th/\({}^{226}\)Ra, \({}^{40}\)K/\({}^{232}\)Th, and \({}^{40}\)K/\({}^{226}\)Ra, respectively. The activity ratios of \({}^{232}\)Th/\({}^{226}\)Ra ranged from 0.82 to 1.86, with an average value of 1.43 \(\pm\) 0.22, as shown in Figure 4a. The majority of the ratios (90%) were greater than 1.20, with the exception of the S10 sample which had a ratio of less than 1.0. The activity ratios had a CV value of 15.6%, which indicates a weak variation of ratios. The \({}^{232}\)Th/\({}^{226}\)Ra ratio was greater than 1.0, signifying that the thorium and uranium decay series were at disequilibrium and that Th-bearing minerals were higher than Ra-bearing minerals [9; 54; 55]. The average activity ratio was close to the ratio of the world soil average of 1.41, with mean concentrations of 45 Bq/kg and 32 Bq/kg for \({}^{232}\)Th and \({}^{226}\)Ra, respectively [14]. An average mean activity ratio close to 1.41 has been observed in China [56] and Egypt [30; 57]. The ratio depends on the area's local geological and geochemical settings [9]. Several studies have observed \({}^{232}\)Th/\({}^{226}\)Ra activity ratios higher than those found in the present study [47; 55; 55; 58]. In contrast, some studies have reported lower activity ratios than those found in this study [9; 32].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Nuclide** & **pH** & **EC (μs/cm)** & **OM (\%)** & **Clay (\%)** & **Silt (\%)** & **Sand (\%)** \\ \hline \({}^{40}\)K & 0.03 & 0.00 & 0.02 & 0.59 *** & 0.11 & \(-\)0.52 ** \\ \({}^{232}\)Th & \(-\)0.18 & 0.12 & 0.10 & 0.50 ** & 0.19 & \(-\)0.48 ** \\ \({}^{226}\)Ra & \(-\)0.08 & 0.40 * & 0.05 & 0.44 * & 0.09 & \(-\)0.39 * \\ \hline \hline \end{tabular}  
* \(p<\) 0.05, ** \(p<\) 0.01, *** \(p<\) 0.001.  
\end{table}
Table 6: Linear correlation coefficient of \({}^{40}\)K, \({}^{232}\)Th, and \({}^{226}\)Ra activity concentrations with soil properties.  
The ratios of \({}^{40}\)K/\({}^{232}\)Th (Figure 3b) varied from 8.47 to 15.67, with an average ratio of 13.1 \(\pm\) 1.9. The CV value of 14.4% indicates low variation. The ratios of \({}^{40}\)K/\({}^{226}\)Ra (Figure 3c) varied between 10.2 and 26.8, with an average ratio of 18.8 \(\pm\) 4.1. The CV value of 22.1% indicates moderate variation. Additionally, the \({}^{40}\)K/\({}^{232}\)Th and \({}^{40}\)K/\({}^{226}\)Ra ratios in the soil samples were higher than the world average values of 9.3 and 13.1, respectively [14]. The higher ratios suggest that the mineral composition of the soil samples contained light minerals such as sandstone and limestone [9; 55]. This confirmed the relatively low activity concentrations of natural radionuclides in comparison to world average concentrations in the soil.