# Natural Radioactivity and Radon Exhalation from Building Materials in Underground Parking Lots
## 1 Introduction  
Ionizing radiation is one of the factors that can have a negative impact on human health. Natural radiation such as cosmic radiation, radionuclides in the soil and construction materials, radon gas are the highest sources of human radiation exposure. Even low doses of ionizing radiation can cause chronic diseases, cancer can also lead to various negative health effects. Negative consequences can occur many years after exposure. It is impossible to avoid the impact of radiation, but it can be reduced. \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K in construction materials is an important source of human exposure [1, 2]. Gamma radiation of these natural radionuclides causes external exposure. Building materials can be radioactive for various reasons, mostly due to the raw materials with a high activity concentration of natural radionuclides that are used for their production. Therefore, it is important to control the activity concentration of radionuclides in construction materials. One of the ways to reduce the external exposure dose is to select building materials with the low-level activity of radionuclides. Calculation of doses due to radionuclides in building materials is important from the point of radiation safety. High activities of natural radionuclides in building materials may be the cause of higher dose rates indoors, especially when products from various industries are used in the production process [3]. Radon exhalation from building materials is also an important problem as this radioactive inert gas is the most important source of internal exposure. According to some studies, radon and its decay products determine about 50% of the total dose from naturalradiation [4; 5]. Although the main source of radon indoors is soil, in some cases, the main sources of indoor radon can be construction materials--contribution is estimated to be up to 30% [6]. Radon is an alpha emitter; therefore, radon radiation is easily absorbed by human skin. However, radon gas can be inhaled by humans, and radon decay products (\({}^{218}\)Po, \({}^{214}\)Pb, and \({}^{214}\)Bi) can cause internal exposure [7]. The main risk posed by radon and its progeny is that it can cause respiratory tract and lung cancer. Radon disperses rapidly outdoors and is not a health issue. Most radon exposure occurs indoors where radon can have high activity concentration. It has been evaluated that the equivalent dose rate caused by ionizing radiation of radon progeny \({}^{214}\)Pb and \({}^{214}\)Bi can vary from 2 to 20% of the total equivalent dose rate [8; 9]. The average annual effective dose from natural sources is 2.4 mSv: 1.1 mSv of it is due to the basic background radiation, 1.3 mSv due to exposure to radon [10]. According to Lithuanian Hygiene Norms and European Union directives, the indoor radon concentration must not exceed 300 Bq m\({}^{-3}\)[11; 12]. The exposure of radon progeny concentration in underground parking lots is determined by the ventilation intensity and radon exhalation from the soil and building materials. To reduce the amount of radioactive inert gas in parking places, it is necessary to study and use emanation blocking means in building materials; it is also important to know and control the activity concentration of \({}^{226}\)Ra in soil and building materials, as the intensity of radon exhalation depends on it [13]. It has been evaluated that the used quantity of building material and its particular place in a building determines the exposure [14]. In order for the population to be exposed to less radiation from radionuclides in construction materials, the activity concentration of radionuclides in building materials used in the construction must not exceed predefined limit values. Indoor radon research is carried out regularly. After assessing the exposure to ionizing radiation from radionuclides in building materials and the change and formation of this exposure, it is possible to plan measures that must be taken to optimally reduce the exposure.