# Natural Radioactivity and Radon Exhalation from Building Materials in Underground Parking Lots
## 3 Results and Discussion
### Estimation of Radium, Thorium, and Potassium in Various Samples  
The activity concentration (\(C\), Bq kg\({}^{-1}\)) of potassium, thorium, and radium were calculated using the following Equation (3) [26]:  
\[C=\frac{CPS\times 100\times 100}{B.I.\times E_{ff}\times m}\pm\frac{SD_{CPS} \times 100\times 100}{B.I.\times E_{ff}\times m} \tag{3}\]  
where _CPS_ is the net count rate per second, _SD\({}_{CPS}\)_ is the standard deviation of net count rate per second, _B.I._ is the branching intensity, _E\({}_{ff}\)_ is the efficiency of the detector, and \(m\) is sample mass in kg. Table 2 shows the average activity concentrations of the radionuclides \({}^{40}\)K, \({}^{232}\)Th, and \({}^{226}\)Ra in structural materials used for building underground parking lots, as well as the corresponding standard deviation in the materials under investigation. It has been determined a wide range of activity concentrations of natural radionuclides contained in building materials: \({}^{40}\)K--13-1217 Bq kg\({}^{-1}\), \({}^{226}\)Ra--2-124 Bq kg\({}^{-1}\), \({}^{232}\)Th--1-72 Bq kg\({}^{-1}\). The lowest activity concentrations of natural radionuclides have been found in sand, cement, and gravel, while their highest activity concentrations have been measured in ferroc concrete, clay, and concrete. The commonly used building materials samples satisfy the safety criterion of the recommended safety limit for the public [27]. Therefore, these samples do not pose any health hazard for the human. The values of activity indexes \(I_{\gamma}\) and \(I_{\alpha}\) are given in Table 2. These indexes are used for the overall evaluation of building materials from the view of radiation protection. The gamma activity index (\(I_{\gamma}\)) is calculated using the following Equation (4):  
\[I_{\gamma}=\frac{C_{\text{Ra}}}{300}+\frac{C_{\text{Th}}}{200}+\frac{C_{\text{ K}}}{3000} \tag{4}\]  
where \(C_{\text{Ra}}\), \(C_{\text{Th}}\), \(C_{\text{K}}\) are activity concentrations of \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K in Bq kg\({}^{-1}\). The gamma activity indexes of natural radionuclides in building materials varied from 0.14 to 0.67. They did not exceed the values determined by the Lithuanian Hygiene Norm [28] and regulated by the European Commission [29]. Alpha index (\(I_{\alpha}\)) assesses internal hazards originating from the alpha activity of building materials. This parameter evaluates the exposure level due to radon inhalation originating from building materials. The \(I_{\alpha}\) has been proposed by [PERSON] [30]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Building Material**} & \multicolumn{2}{c}{\({}^{40}\)**K**} & \({}^{232}\)**Th** & \({}^{226}\)**Ra** & \\ \cline{2-5}  & **M.V. \(\pm\)**\(\sigma\)** & **M.V. \(\pm\)**\(\sigma\)** & **M.V. \(\pm\)**\(\sigma\)** & **I\({}_{\gamma}\)** & **I\({}_{\alpha}\)** \\  & **(Range)** & **(Range)** & **(Range)** & **(Range)** & \\ \hline \multirow{2}{*}{Clay} & 493 \(\pm\) 16 & 8 \(\pm\) 2 & 24 \(\pm\) 2 & \multirow{2}{*}{0.28} & \multirow{2}{*}{0.12} \\  & (108–734) & (2–16) & (10–41) & & \\ \hline \multirow{2}{*}{Cement} & 126 \(\pm\) 17 & 5 \(\pm\) 1 & 39 \(\pm\) 4 & \multirow{2}{*}{0.20} & \multirow{2}{*}{0.20} \\  & (13–362) & (1–8) & (7–66) & & \\ \hline \multirow{2}{*}{Sand} & 232 \(\pm\) 21 & 5 \(\pm\) 1 & 12 \(\pm\) 1 & \multirow{2}{*}{0.14} & \multirow{2}{*}{0.06} \\  & (137–460) & (1–19) & (5–17) & & \\ \hline \multirow{2}{*}{Gravel} & 301 \(\pm\) 11 & 5 \(\pm\) 1 & 18 \(\pm\) 1 & \multirow{2}{*}{0.19} & \multirow{2}{*}{0.09} \\  & (118–342) & (1–9) & (2–23) & & \\ \hline \multirow{2}{*}{Concrete} & 581 \(\pm\) 27 & 29 \(\pm\) 3 & 44 \(\pm\) 3 & \multirow{2}{*}{0.48} & \multirow{2}{*}{0.22} \\  & (18–1217) & (2–47) & (3–92) & & \\ \hline \multirow{2}{*}{Ferroconcrete} & 603 \(\pm\) 21 & 34 \(\pm\) 4 & 90 \(\pm\) 4 & \multirow{2}{*}{0.67} & \multirow{2}{*}{0.45} \\  & (47–1108) & (1–72) & (4–124) & & \\ \hline \hline \end{tabular}
\end{table}