Abstract
It was developed an improved theoretical model capable to estimate the radium concentration in building materials solely measuring the radon-222 concentration in a confined atmosphere.This non-destructive technique is not limited by the size of the samples, and it intrinsically includes back diffusion.The resulting equation provides the exact solution for the concentration of radon-222 as a function of time and distance in one dimension.The effective concentration of radium-226 is a fit parameter of this equation.In order to reduce its complexity, this equation was simplified considering two cases:low diffusion in the building material compared to the air, anda building material initially saturated with radon-222.These simplified versions of the exact one dimension solution were used to fit experimental data.Radon-222 concentration was continuously measured for twelve days with an AlphaGUARD detector, located at the Laboratory of Applied Nuclear Physics at Universidade Tecnologica Federal do Parana (UTFPR).This model was applied to two different materials: cement mortar and concrete, which results were respectively (15.7 +- 8.3) Bq/kg and (10.5 +- 2.4) Bq/kg for the radium-226 effective concentration.This estimation was confronted with the direct measurements of radium in the same materials (same sources) using gamma-ray spectrometry, fulfilled at Centro de Desenvolvimento da Tecnologia Nuclear (CDTN), which results were respectively (13.81 +- 0.23) Bq/kg and (12.61 +- 0.22) Bq/kg.
Highlights
Building materials such as concrete, cement, brick, and gypsum usually present small amounts of radioactive elements
2019 exposure is due to sources in the surroundings, outside the individual’s body. This is the case of radium-226 present in a building material, which decays by alpha emission into radon-222, subsequently emitting a gamma ray
Both advective-diffusive model (ADM) and dusty-gas model (DGM) have the contribution of the pressure and concentration gradients, in DGM the multiplying factors of the gradients are depend on the mole fractions
Summary
Building materials such as concrete, cement, brick, and gypsum usually present small amounts of radioactive elements. In 2002, Ferry et al proposed a non-destructive technique to determine the emanation factor in small rocks using accumulation chambers [31] In this method, the samples must be smaller than the diffusion length. In 2004, Jang et al proposed a mathematical model to estimate the radon-222 mean concentration in a confined atmosphere [32] This model uses the equilibrium concentration along the external atmosphere to derive the exhalation rate as a function of concentration. It is proposed an improved equation to describe the mean radon-222 concentration in a confined atmosphere as a function of time By using this mathematical model, it is possible to estimate the radium-226 effective concentration in materials using experimental data concerning the radon-222 activity
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