# Natural Radioactivity and Radon Exhalation from Building Materials in Underground Parking Lots
## 3 Results and Discussion  
### Radon Exhalation Rate  
Radon surface and mass exhalation rates were calculated using Equations (1) and (2), respectively [15; 18]. \[E_{\rm S}=\frac{CV\lambda/A}{T+(1/\lambda)\big{(}e^{-\lambda T}-1\big{)}} \tag{1}\]  
and  
\[E_{\rm M}=\frac{CV\lambda/M}{T+(1/\lambda)\big{(}e^{-\lambda T}-1\big{)}} \tag{2}\]  
where \(E_{\rm S}\) is surface exhalation rate (Bq m\({}^{-2}\) h\({}^{-1}\)); \(E_{\rm M}\) is mass exhalation rate (Bq kg\({}^{-1}\) h\({}^{-1}\)); \(C\) is integrated radon exposure (Bq m\({}^{-3}\) h\({}^{-1}\)); \(V\) is the volume of air (m\({}^{3}\)); \(\lambda\) is radon decay constant (h\({}^{-1}\)); \(T\) is the exposure time (h), \(A\) is the surface area (m\({}^{2}\))m and \(M\) is the mass (kg) of the sample, respectively. Radon surface and mass exhalation rates and other parameters of the most commonly used building materials are presented in Table 1.  
Radon surface exhalation rates vary from 10.2 \(\pm\) 0.5 to 26.2 \(\pm\) 0.4 mBq m\({}^{-2}\) h\({}^{-1}\); radon mass exhalation rates vary from 1.12 \(\pm\) 0.06 to 2.95 \(\pm\) 0.07 mBq m\({}^{-2}\) h\({}^{-1}\) (uncertainties are given with coverage factor \(k\) = 2). The maximum rate of radon exhalation was observed in the concrete and ferroconcrete samples. It is worth mentioning that the radon exhalation rate changes with the age of the concrete. Various researchers [3; 19; 20; 21] estimated that the radon exhalation rate was decreased with the increasing age of concrete. Additionally, it was estimated that the radon exhalation rate of concrete is reduced by low humidity conditions. Therefore, the results show that radon exhalation from samples of concrete measurements is dependent on the humidity and age of the sample and should be standardized. Radon surface exhalation and mass exhalation rates found for sand are the lowest values and for concrete and ferroconcrete are found to be the maximum. The emanation fraction varies from 5 to 16%. The results obtained in this work are within the values measured in other countries [18; 22; 23; 24; 25]. Correlation analysis showed a strong positive correlation (0.88) between radon concentration and radium activity concentration in various samples, which may be due to the radium content and porosity in the samples (Figure 1). Research of radon activity concentrations in underground parking lots with workplaces has shown that people work in a safe environment in terms of radiation safety. The radon activity concentration varied from 22 \(\pm\) 3 to 270 \(\pm\) 18 Bq m\({}^{-3}\) (the average value was 83 \(\pm\) 7 Bq m\({}^{-3}\)). Indoor radon activity concentration did not exceed the level of the Lithuanian hygiene standard [11]. However, several cases were close to the maximum level. Such results may have been due to the fact that no mechanical ventilation systems were installed that do not allow radon to accumulate on the lower floors of the building. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Building Material**} & **Rn Surface** & **Rn Mass** & & & \\  & **Exhalation Rate** & **Exhalation Rate** & **Emanion Factor (\%)** & **Porosity (\%)** & **Bulk Density** \\  & **(mBq\(\cdot\)m\({}^{-2}\)\(\cdot\)h\({}^{-1}\))** & **(mBq\(\cdot\)kg\(\cdot\)1\(\cdot\)h\({}^{-1}\))** & **(**)** & **(**)** \\ \hline Sand & 10.2 \(\pm\) 1.5 & 1.12 \(\pm\) 0.16 & 5 \(\pm\) 0.7 & 32 \(\pm\) 3.5 & 1620 \\ \hline Clay bricks & 18.3 \(\pm\) 1.3 & 1.22 \(\pm\) 0.15 & 3 \(\pm\) 0.5 & 23 \(\pm\) 3.2 & 1950 \\ \hline Cement & 19.9 \(\pm\) 1.6 & 1.19 \(\pm\) 0.13 & 11 \(\pm\) 1.9 & 12 \(\pm\) 2.2 & 2020 \\ \hline Concrete & 24.3 \(\pm\) 1.2 & 2.93 \(\pm\) 0.18 & 10 \(\pm\) 1.3 & 16 \(\pm\) 2.6 & 2200 \\ \hline Ferroconcrete & 26.2 \(\pm\) 1.4 & 2.95 \(\pm\) 0.17 & 16 \(\pm\) 2.1 & 18 \(\pm\) 2.9 & 2400 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Radon surface and mass exhalation rates and other parameters of studied building materials (M.V. \(\pm\) \(\sigma\)). Figure 1: The correlation between radon concentration and radium activity concentration.