Study On Inhabitant Radiation Dose Model Induced By Building Material And Fast Measurement Of Radon Emanation Coefficient

BackgroundWith the accelerating of industrialization and urbanization in China, the demand of building materials is getting huge. In addition, new type of building materials develop rapidly and are used widely following the implementing of "energy conservation and emission reduction, resource protection" policies. However, the huge change in manufacturing process and raw materials results in a certain deviation of inhabitant dose indued by building materials based on tranditional model, which could go against the effective protection of inhabitant health or hinder the development of new type of building materials and rational utilization of slag.ObjectiveTo study and analyze the influence on the calculation of inhabitant dose by building materials imposed by several parameters, such as density, thickness, type of building materials and dose reference point as well as radon emanation coefficient. To assess the radiological hazard of building materials by establishing a new model of inhabitant dose from building materials by introducing the correcting parameters those suggesting relatively higher influence. To establish a fast method to measure radon emanation coefficient of building materials, and study the changing rule between radon emanation coefficient and the moisture content, temperature and humidity.Methods(1) Based on Monte Carlo method, a classical room structure(4m×5m×2.8m, with window and door) was set up to calculate the specific effective dose rate to the inhabitant, while4walls, ceiling and floor of the room filled with different types of building materials of different densities and thicknesses by MCNPX code. The equation between specific effective dose rate and surface density of building materials was obtained through nonlinear regression analysis and was introduced to external dose calculation model which is validated by on-site measurement. The equation between inhabitant internal dose rate and radon emanation coefficient, density and thickness was obtained by theoretical analysis of radon transport mechanism in building materials.(2) A math equation to rapidly measure radon emanation coefficient of building materials was obtained by analyzing the radon transportation law inside the building materials itself and sealed chamber. By taking aerated concrete as sample, the optimized measure time is determined, and the influence of sample thickness and reproducibility of the method were studied using continual radon monitor and sealed chamber as well as vacuum cement. The reliability of the fast method was validated through comparing with long time measuring method suggested by standard.(3) The radon emanation coefficient of aerated concrete with different moisture content (0%,2%,5%,10%,20%,25%,30%,35%,40%,45%,53%and60%)and under different temperature (10,17,20,25,30,35and40℃)and humidity (12%,33%,60%,79%and95%)was measured by the fast method established above. The changing rule between radon coefficient and moisture, temperature and humidity was analyzed by regression method.Results(1) The type of building materials, positions of dose reference point impose no significant influence to inhabitant dose. However, the density, thickness and radon emanation coefficient show significant influence to inhabitant dose by building materials, suggesting that correcting is needed to be carried out. The specific effective dose rates to habitant by40K、238U series�'�232Th series contained in building materials, show an exponential growth trend following the increase of surface density(density×thickness).(2) By merging inhabitant external and internal dose, a model of inhabitant dose induced by building materials was established as following:where E is the specific dose rate to inhabitant by building materials, nSv·h-1. Ck, CRa and CTh is the specific effective dose rate induced by40K、238U series and232Th series radioisotope contained in building materials,(nSv·h-1)·(Bq·kg-1)-1. Ak, ARa and ATh is the specific activity of40K、226Ra and232Th, Bq-kg-1.ε is radon emanation coefficient of building materials. ρ is density, kg·m-3. d is thickness, m. In addition, inhabitant external dose model is validated by on-site measurement results, suggesting a certain level of reliability of the model.(3) For the fast method of radon emanation coefficient, the measuring time of24～60h produce relative stable results and can be chose as optimized measure time. The radon coefficients of sample with different thicknesses show no significant difference (P>0.05) on condition that sample thickness less than diffusion0.4×length. The results from fast method show a good accordance with that from long time measurement proposed by standard (P>0.05)。(4) Radon emanation coefficient of aerated concrete shows a logarithmic growth following the increase of moisture content: ε=0.096·ln(s>+2.43)+0.037(R2=0.952); Radon emanation coefficient of aerated concrete shows a linear growth with the increase of temperature:ε=0.00245·T+0.0601(R2=0.987). The results under different humidity differs no significantly (P>0.05)Conclusion:In this thesis, a new model of inhabitant dose induced by building materials was established by introducing3parameters such as thickness, density and radon emanation coefficient to correct the calculation, so as to provide precise and rational assessment of inhabitant dose with dosimetric basis, to provide the formulating and revising of standard to assess and control the radiological hazard of building materials and to not only protect the inhabitant health but also promote the development of new type of building material and rational recycle of industrial slag.The fast method to measure the radon emanation coefficient was established, so as to improve the measuring efficiency and promote the development radiation protection measurement technology, is a good supplement for the popularization and application of dose model newly established.