# Natural Radioactivity and Radon Exhalation from Building Materials in Underground Parking Lots
## 2 Materials and Methods  
The measurements were undertaken in typical parking lots, located one floor below dwellings or shopping centers. Samples were taken in several ways. Some samples were collected from manufacturers and suppliers. Other samples, if it was possible, were taken at underground parking lots. For the statistical evaluation of the activity concentration distribution of natural radionuclides, 20 to 50 samples of the same material were taken.  
To identify gamma radionuclides \({}^{40}\)K, \({}^{232}\)Th, \({}^{226}\)Ra and measure their activity concentration the samples of the main building materials used for the construction of underground parking lots (clay, cement, sand, gravel, concrete, and ferroc concrete) were prepared for spectrometric analysis. The samples were dried at 105 \({}^{o}\)C in a laboratory oven, then crushed and homogeneously put into measuring containers of 200 mL and left for four weeks to reach secular equilibrium between \({}^{226}\)Ra and its progeny. The samples were analyzed with the gamma spectrometry system Canberra, USA, with the semiconductor Hyper Pure germanium (HPGe) detector (model GC2520). HPGe detector has an energy resolution full width at half-maximum (FWHM) of 1.9 keV at 1330 keV (\({}^{60}\)Co). The detector has a high peak to Compton ratio of 58:1 and relative efficiency of 30%. The samples of building materials were measured spectrometrically for at least 90 000 s. \({}^{226}\)Ra activity concentration in the samples was defined based on its decay products \({}^{214}\)Pb (352 keV) and \({}^{214}\)Bi (609 keV), while \({}^{232}\)Th was defined based on \({}^{228}\)Ac (911 keV) and \({}^{208}\)Tl (583 keV). \({}^{40}\)K was determined directly according to the 1460 keV energy gamma-radiation peak.  
The radon exhalation rate was measured by hermetically closing the sample in a container and observing the radon activity growth as a time function [3; 15; 16]. The samples were kept in cylindrical containers of 400 mL capacity. LR-115 track detector was used in this study. The detector is exposed to the exhaled radon from the sample and fixes \(\alpha\)-particles resulting from the radon progeny in the volume of the container and \({}^{218}\)Po and \({}^{214}\)Po deposited on the inner walls of the container. Following the long-term exposure, the LR-115 detector was chemically etched for developing the tracks registered in the films and the concentrations of radon and its decay products were determined.  
The equivalent dose rate (EDR, nSv h\({}^{-1}\)) caused by natural radionuclides in underground parking lots building materials was measured. Dosimetric measurements were performed using an InSpector 1000 a high-performance digital handheld multichannel analyzer with a NaI detector (IPROS-3), energy range 50 keV to 3 MeV [17]. The analyzer has computer interface software Genie 2000. The equivalent dose results are updated once per second. The parking lot where the EDR was measured (no closer than 50 cm from the wall) was split into imaginary squares with an edge length of 2 m. The average EDR value of the five measurements was recorded at the center of each imaginary square with the detector held at a height of 1 m. The number of measurement points depends on the size of the parking lot.  
At the same time, radon concentration was measured using radon and thoron measurement system SARAD RTM2200. The monitor is based on \(\alpha\)-spectrometry forming \({}^{222}\)Rn progeny (\({}^{218}\)Po and \({}^{214}\)Po) inside the high-quality silicon radiation detector chamber. Radon progeny deposit on the surface of the semiconductor detector and alpha radiation was registered. Measurement upper range of the radon concentration is 10 MBq m\({}^{-3}\), device sensitivity--3 or 7 ppm/(kBq\(\cdot\)m\({}^{-3}\)) for fast or slow mode. Radon concentrations can be registered at different time intervals.