Speaker
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Exposure of the population to indoor radon is one of the leading causes of lung cancer [1]. Building materials are a recognized source of indoor radon [2], and current national and international regulations [e.g., 3] require consideration of the specific contribution of building materials to indoor radon concentration. This contribution is generally quantified by means of the exhalation rate, i.e., the radon activity that escapes from the surface of a building element (e.g., a wall) per unit of surface area and time. The exhalation rate can be evaluated analytically or measured experimentally.
The first approach involves applying case-specific solutions of the general transport equation for radon in porous media [4]. The main limitation of this approach is the need for a large set of parameters—often very difficult to determine—to accurately characterize the emitting artifact. The second method, on the other hand, involves measuring the radon exhalation rate on a representative sample of the building material [5] and subsequently correlating it theoretically with the actual exhalation rate from the existing artifact [6, 7]. The main criticalities in this case are represented by (i) the difficulty of obtaining a representative sample of the building material due to its often unknown composition, and by the impossibility of considering (ii) the advective contribution to radon transport through the artifact and (iii) the influence on the exhalation rate of installation conditions (e.g., the bonding and covering materials used in the artifact [8]) and environmental conditions (i.e., temperature and humidity [9]).
The limitations of the two currently employed approaches are overcome if the measurement of the radon exhalation rate is carried out directly on the surface of the existing building element (e.g., a wall) using, for example, the method reported in the ISO 11665-7 standard. The main problem related to this technique—and which has most hindered its use—is that of guaranteeing the tightness of the system, especially at the interface between the accumulation chamber and the surface of the exhaling material [10].
An innovative device, called SIREN, was specifically developed, at the Laboratory of Radioactivity of the Italian National Institute of Health, to measure in-situ the radon exhalation rate from the internal surfaces of walls. The equipment has been designed and developed to overcome all the main limitations that have discouraged the use of this approach in the evaluation of the contribution of building materials to indoor radon concentration.
The apparatus has been subjected to commissioning, experimentally evaluating its tightness and repeatability of measurements. The device's sealing system, based on a complex of pressing springs that exploit friction with the underlying surface to exert pressure on the accumulation chamber, has been studied, showing that the results do not differ statistically significantly from destructive accumulation systems based on mechanical clamping techniques (e.g., anchors and expansion screws). The repeatability of the measurements, evaluated for two levels of the measurand, was found to be below 10%. A measurement and data analysis protocol has been specifically developed to guarantee and control the accuracy of the measurement with respect to the main interfering phenomena during measurements.
The developed apparatus is portable and allows for rapid and non-destructive measurements of the effective contribution of building materials to indoor radon concentration, considering both atoms generated by the materials and those produced elsewhere and transported through the building element. The results of in-situ measurements conducted using SIREN can provide a decisive contribution to improving the specificity, and therefore the effectiveness, of remediation interventions to reduce indoor radon concentration.
The project is completely open source to promote the dissemination of the test method and contribute to its standardization: 3D printing models and algorithms will be soon made available online.
References
[1] World Health Organization, WHO handbook on indoor radon: a public health perspective, in: W.H. Organization (Ed.), 2009.
[2] UNSCEAR, Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2008 report: report to the General Assembly, with Scientific Annexes, in, 2008.
[3] European Commission, Council Directive 2013/59/Euratom: basic safety standards for protection against the dangers arising from exposure to ionising radiation, in: E. Commission (Ed.), Official Journal of the European Union, 2014, pp. 1-73.
[4] C. Di Carlo, A. Maiorana, M. Ampollini, S. Antignani, M. Caprio, C. Carpentieri, F. Bochicchio, Models of radon exhalation from building structures: General and case-specific solutions, Sci Total Environ, 885 (2023) 163800.
[5] Y. Ishimori, K. Lange, P. Martin, Y.S. Mayya, M. Phaneuf, Measurement and calculation of radon releases from NORM residues, in: Technical Reports, International Atomic Energy Agency, Vienna (Austria), 2013.
[6] B.K. Sahoo, B.K. Sapra, J.J. Gaware, S.D. Kanse, Y.S. Mayya, A model to predict radon exhalation from walls to indoor air based on the exhalation from building material samples, Sci Total Environ, 409 (2011) 2635-2641.
[7] M. Orabi, Estimation of the radon surface exhalation rate from a wall as related to that from its building material sample, Canadian Journal of Physics, 96 (2018) 353-357.
[8] C. Wang, D. Xie, C.W. Yu, H. Wang, Evaluation of the effect of cover layer on radon exhalation from building materials, Indoor and Built Environment, 30 (2020) 1390-1399.
[9] C. Di Carlo, A. Maiorana, F. Bochicchio, Indoor Radon: Sources, Transport Mechanisms and Influencing Parameters, 2023.
[10] A. Noverques, G. Verdú, B. Juste, M. Sancho, Experimental radon exhalation measurements: Comparison of different techniques, Radiation Physics and Chemistry, 155 (2019) 319-322.