Proučavanje emanacije, ekshalacije i mernih tehnika radona
Investigation of radon emanation, exhalation and measuring
Докторанд
Stajić, JelenaМентор
Nikezić, DragoslavЧланови комисије
Udovičić, VladimirStevanović, Nenad
Метаподаци
Приказ свих података о дисертацијиСажетак
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.