# Natural Radioactivity and Radon Exhalation from Building Materials in Underground Parking Lots
## 3 Results and Discussion
### Evaluation of Radiological Hazard Parameters in Building Materials
#### 3.3.2 Absorbed and Annual Effective Dose Rate  
Gamma radiation hazards related to building materials can be evaluated by calculating the different radiation hazard parameters [34]. One of the parameters to estimate radiation risk to humans is absorbed dose rate (\(D\)). The absorbed dose rate can be calculated by the concentrations of \({}^{40}\)K, \({}^{226}\)Ra, and \({}^{232}\)Th by applying the conversion factors 0.0417, 0.462,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Building Material**} & \multirow{2}{*}{\begin{tabular}{c} \(Ra_{\text{eq}}\) \\ (Bq kg\({}^{-1}\)) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Average Absorbed** \\ **Dose Rate (nGy h\({}^{-1}\))** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Outdoor Annual** \\ **Effective Dose** \\ **(mSv)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Indoor Annual** \\ **Effective Dose** \\ **(mSv)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} \(H_{\text{ex}}\) \\ **(mSv)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} \(H_{\text{in}}\) \\ \end{tabular} } \\ \hline Clay & 73 & 36 & 0.045 & 0.18 & 0.20 & 0.26 \\ \hline Cement & 56 & 26 & 0.032 & 0.13 & 0.15 & 0.26 \\ \hline Sand & 37 & 18 & 0.022 & 0.09 & 0.10 & 0.13 \\ \hline Gravel & 48 & 24 & 0.029 & 0.12 & 0.13 & 0.18 \\ \hline Concrete & 130 & 62 & 0.076 & 0.31 & 0.35 & 0.47 \\ \hline Ferroconcrete & 185 & 87 & 0.107 & 0.43 & 0.50 & 0.74 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The average values of absorbed dose rate, annual effective dose, and hazard parameters for building materials.  
and 0.604 for potassium, radium, and thorium, respectively [32]. These conversion factors were used to calculate the total absorbed gamma dose rate in the air of underground car parks at 1 m above the ground level. The absorbed dose rate has been calculated by using the Monte Carlo method [35]:  
\[D=0.0417\mathrm{C_{K}}+0.462\mathrm{C_{Ra}}+0.604\mathrm{C_{Th}} \tag{7}\]  
where \(D\) is the absorbed dose rate (nGy h\({}^{-1}\)).  
To determine annual effective dose (_AED_) the conversion coefficient from absorbed dose to effective dose and the indoor and outdoor occupancy factor must be taken into account. The conversion coefficient from absorbed dose rate in the air to effective dose is 0.7 Sv Gy\({}^{-1}\), which is used to convert the absorbed dose rate to human effective dose equivalent with an outdoor occupancy of 20% and 80% for indoors, proposed by [32].  
The annual effective doses are calculated as follows:  
\[AED_{outdoor}=0.2\times D\times t\times F\times 10^{-6} \tag{8}\]  
\[AED_{indoor}=0.8\times D\times t\times F\times 10^{-6} \tag{9}\]  
where _AED_ is the annual effective dose (mSv y\({}^{-1}\)); \(D\) is absorbed dose rate (nGy h\({}^{-1}\)); \(t\) is the duration of the exposure (8760 h); \(F\) is the conversion factor of 0.7 Sv Gy\({}^{-1}\).  
Applying Equations (7)-(9), the absorbed and annual effective dose rates from the samples were calculated, as given in Table 3. The average values of the calculated absorbed dose rate in samples ranged from 18.24 nGy h\({}^{-1}\) in the sand to 87.26 nGy h\({}^{-1}\) in ferroc concrete. The values of _AED_indoor were found to vary from 0.09 to 0.43 mSv y\({}^{-1}\). _AED_outdoor varied from 0.022 to 0.107 mSv y\({}^{-1}\). The annual effective dose from ferroc concrete is higher than the other samples. The lowest annual effective dose was found in sand and gravel. However, it was estimated that all these building materials samples satisfy the safety criteria for radiation safety point of view, and hence, these samples do not pose any environmental and health hazard problems. The calculated annual effective dose is below the limit of 1.0 mSv y\({}^{-1}\) recommended by the International Commission on Radiological Protection for the general public.