Proučavanje emanacije, ekshalacije i mernih tehnika radona
Investigation of radon emanation, exhalation and measuring
Committee membersUdovičić, Vladimir
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An algorithm for theoretical calculation of radon 222Rn emanation fraction in granular materials was presented. The emanation based on radon recoil following the decay of 226Ra and alpha particle emission was considered. Monte Carlo method and analytical approach were both applied. The results of the calculations were quite low in comparison to the experimental data, especially in the case of uniform distribution of 226Ra within a grain. This could be explained by inhomogeneous distribution of radium in a solid grain, the existence of pores inside the grain structure and the contribution of other mechanisms of emanation. The rates of radon 222Rn exhalation from some building materials were measured experimentally using a chamber connected to RAD7 device. Fitting the growth curves of radon concentration in the chamber provided the information on radon exhalation rates. The values ranged from 1.4 mBq m-2 h-1 to 855 mBq m-2 h-1 for solid samples and from 1.3 mBq kg-1 h-1 to 11.4 mBq kg-1 ...h-1 for powdered samples. Gamma-spectrometry of the samples was performed using HPGe detector. The average specific activities of 226Ra, 232Th and 40K were 35, 39 and 368 Bq kg-1, respectively. No significant correlation was found between radon exhalation rates and the specific activities of 226Ra in the samples. An analytical approach for calculating the geometrical efficiency of a circular detector for particles with a finite range, emitted from a point-like source, was presented. The problem of critical detection angle was also considered. The method can be applied to measuring the concentrations of radon and its decay products using solid state nuclear track detectors. The results of analytical calculation were compared to the values obtained by Monte Carlo Method. Computer software for calculation of the calibration coefficient of a CR-39 detector for radon concentration measurements was also described. The detector closed in a cylindrical or conical diffusion chamber was analyzed. The software may be used for optimization of the diffusion chamber, detector dimensions and the complete measurement procedure. The results obtained for five different V functions were compared with some experimental values found in the literature. The well-known method of radon and thoron progeny concentration measurements, based on air filtration followed by total alpha counting, was analyzed in order to assess the reliability of the method. The reasons for obtaining unrealistic or incorrect results were examined. Due to the system sensitivity to statistical errors the method appears to be quite unreliable, especially in the case of low progeny concentrations in air. Radon activity concentrations in all public schools and kindergartens located in the city area of Kragujevac were measured. UFO passive discriminative radon/thoron detectors were used and radon calibration coefficient was obtained using RAD7 device. The obtained values are relatively low and they do not exceed the proposed limit of 200 Bq m-3.