|M.Sc Student||Levit Aviel|
|Subject||Effect of Ambient Conditions on the 222Rn Exhalation Rate|
from Cementitious Building Blocks
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Konstantin Kovler|
|Professor Rachel Becker|
|Full Thesis text - in Hebrew|
The current research deals with various radon exhalation measurement techniques, methods for analyzing the experimental data and the effect of ambient conditions such as temperature and relative humidity on radon exhalation. Two types of building blocks have been examined: (1) Pumice Block "P " - made with pumice and scoria light-weight aggregates and (2) Regular Concrete Block "R " - made with normal-weight dolomite aggregate.
The technique applied for the exhalation rate measurements is based on the enclosure of the sample under analysis inside a chamber for about 96 hours, and monitoring the radon activity growth inside the chamber as a function of time. Radon concentration inside the chamber has been monitored using two different detectors: a continuous monitor (RAD7 - Solid State Alpha Detector) and integrative monitors (E-perm Electrets).
Four different analysis methods were applied to the continuous monitoring results in order to identify the most reliable one. In the first method, non-linear fitting was used for estimation of the three unknown parameters: initial 222Rn concentration in the chamber, equivalent 222Rn decay rate in the chamber and maximal 222Rn concentration in the chamber. In the second analysis method, the initial concentration was determined first, using a linear regression on the initial period results, and then the exponential regression was applied, using the formerly derived initial concentration as an input. The third method of analysis is radically different from the first two. In this method, only a short part of the accumulation curve was analyzed and the Radon Exhalation Rate was determined by the initial slope. Since the equivalent radon decay rate can not be determined by this method, its value was assumed to be equal to the natural 222Rn decay rate, i.e. the chamber leakage and so called “back diffusion” were neglected. The fourth method is a combination of the second method and the third.
Continuous monitoring and non-linear analysis of the results seem to be the most appropriate measurement and analysis methods. They enable evaluation of the initial radon concentration in the chamber and of the equivalent radon decay rate, and lead to the most accurate estimate of radon exhalation rate. Although, the integrative measurement is a simple and a convenient method, but is associated with a serious uncertainty, that may lead to a non-conservative estimate of radon exhalation due to the lack of information on initial radon concentration in the chamber and on the equivalent radon decay rate.