Thickness of radon emitting layer in building materials

• Published in: Radiation physics and chemistry (Oxford, England : 1993) Vol. 172; p. 108786
• Main Authors: Corrêa, J.N., Silva, A.C.M., Paschuk, S.A., Barreto, R.C., Denyak, V., Schelin, H.R., Narloch, D.C., Hashimoto, Y., Martin, A.C.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.07.2020; Elsevier BV
• Subjects: Building materials; Cement; Cement mortar; Construction materials; Diffusion length; Emitting layer; Exhalation; Mortars (material); Radon; Sand; Thickness measurement; Cement mortar; Radon; Emitting layer
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/j.radphyschem.2020.108786

Human exposure to 222Rn usually occurs in closed environments due to the gas exhaled from the soil and building materials. Since the 222Rn must diffuse through the material before reaching the atmosphere, some of the product decays before. This implies that there is an effective maximum thickness associated with the diffusion length in which the 222Rn exhalation could be neglected. The aim of this research is to identify the effective maximum thickness of exhalation for cement mortar, which is commonly used in civil constructions. With this purpose, the concentration of 222Rn in air produced by 19 cylindrical samples of cement mortar with 5 different thickness was measured. CR-39 detectors mounted in diffusion chambers were used for radon activity measurements. The measured 222Rn activity varied between 214 Bq/m³ and 478 Bq/m³ for the 14 samples of common cement mortar, and between 12.4 × 10³ Bq/m³ and 41.6 × 10³ Bq/m³, for the 5 samples of cement mortar with the addition of radioactive sand, while the thickness of the samples varied between 1.3 cm and 4.5 cm. For the samples from common cement mortar the 222Rn concentration tends to achieve equilibrium plateau when the thickness reaches 2 cm. For samples with radioactive sand the values of radon activity presented a linear growth, indicating that such stability plateau must occur in larger thickness. •Effective value of Radon emitting layer was found for 1.4–4.5 cm thick cement samples.•Radon activity for common cement mortar was 0.2–0.5 kBq/m³.•Radon activity for cement mortar with radioactive sand was 12–41 kBq/m³.•The thickness of Radon emitting layer in common cement mortar was about 2 cm.•In radioactive cement mortar, the thickness of emitting layer is greater than 4.5 cm.