## 3 Results and Discussion  
The Activity Concentrations of Naturally Occurring Radiomuclides (\({}^{238}\)U, \({}^{232}\)Th and \({}^{40}\)K) in Soil  
The statistical parameters for the specific activity of \({}^{238}\)U, \({}^{232}\)Th and \({}^{40}\)K in the collected samples from the Lisava uranium mining sector are presented in Table 2. Appendix A shows the individual results of the gamma spectroscopy of the analyzed soil samples from the study area. The specific activity or activity concentration (activity per unit mass) is expressed in Bq/kg of radionuclides in soil, and the conversions recommended between Bq/kg and ppm are: 1 ppm U = 12.35 Bq/kg, 1 ppm Th = 4.06 Bq/kg and 1% K = 313 Bq/kg [10]. The histograms, Q-Q plots and box plots for these elements are presented in Figure 4. The frequency distribution charts were used to assess the normality distribution of the \({}^{238}\)U, \({}^{232}\)Th and \({}^{40}\)K data sets, and the patterns displayed were multimodal for \({}^{234}\)U and \({}^{40}\)K and unimodal for \({}^{232}\)Th. The fitting curves in the histograms show that the distribution was asymmetrical; they were skewed towards the right for all three elements, but the skewness was more significant for thorium compared to uranium and potassium (the distribution's peak is off center toward the limit, and a tail stretches away from it to the right). The Q-Q plots confirmed the asymmetric distribution for \({}^{238}\)U, \({}^{232}\)Th and \({}^{40}\)K, with the actual data shown on the x-axis and the predicted values for a normal distribution shown on the y-axis. The concavity in the plots denote the lognormal distribution, with low and high values placed below the regression line. The box plots depict the average, minimum and maximum values of the data sets for \({}^{238}\)U, \({}^{232}\)Th and \({}^{40}\)K. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Radiological Parameter** & **Equation** & **References** \\ \hline RRadium equivalent activity (Raeq) & Raeq = A\({}_{\text{U}}\) + 1.43A\({}_{\text{Th}}\) + 0.077A\({}_{\text{K}}\) (Bq/kg) & [27; 28] \\ Absorbed gamma dose rate (DR) & D\({}_{\text{R}}\) = 0.462A\({}_{\text{U}}\) + 0.604A\({}_{\text{Th}}\) + 0.042A\({}_{\text{K}}\) (nGy/h) & [28; 29] \\ External hazard index (Hex) & H\({}_{\text{ex}}\) = (A\({}_{\text{U}}\)/370) + (A\({}_{\text{Th}}\)/259) + (A\({}_{\text{K}}\)/4810) & [27; 30] \\ Representative level index (RLI) & RLI = (1/150A\({}_{\text{U}}\)) + (1/100A\({}_{\text{Th}}\)) + (1/1500A\({}_{\text{K}}\)) & [30; 31] \\ \hline \hline A\({}_{\text{U}}\), A\({}_{\text{Th}}\) and A\({}_{\text{K}}\): specific activity of \({}^{238}\)U, \({}^{232}\)Th and \({}^{40}\)K (Bq/kg); recommended values: Raeq\({}_{\text{-}}\) 370 Bq/kg; D\({}_{\text{R}}\) = 84 nGy/h; Hex \(>\) 1; and RLI \(>\) 1 [27]. \\ \hline \hline \end{tabular} N—no. of samples.  
\end{table} 
Table 1: The calculation equations for radiological parameters. The specific activity of naturally occurring radionuclides varied significantly in the studied area due to the geological features and human activity (uranium mining practices). In all the soil samples, the specific activities were in the following order: \({}^{40}\)K \(>\)\({}^{238}\)U \(>\)\({}^{232}\)Th. The activity concentration of \({}^{238}\)U in all the soil samples showed the biggest variation, ranging from 32.12 to 396.23 Bq/kg with a mean concentration of 197.21 Bq/kg. The calculated statistical parameters (Table 2) and graphic representations for \({}^{238}\)U (Figure 4) indicated a large variation in uranium in the soil and suggested a spatially inhomogeneous distribution. The standard deviation (SD) value for \({}^{238}\)U was relatively high (92.49 Bq/kg) and indicated an asymmetric distribution of the \({}^{238}\)U in the investigated surface soils. The skewness had a positive value, which revealed a positive asymmetry to the right for uranium, whereas the kurtosis parameter had a negative value.