Exploring statistical and machine learning techniques to identify factors influencing indoor radon concentration.

Radon is a radioactive gas with a carcinogenic effect. The malign effect on human health is, however, mostly influenced by the level of exposure. Dangerous exposure occurs predominantly indoors where the level of indoor radon concentration (IRC) is, in its turn, influenced by several factors. The current study aims to investigate the combined effects of geology, pedology, and house characteristics on the IRC based on 3132 passive radon measurements conducted in Romania. Several techniques for evaluating the impact of predictors on the dependent variable were used, from univariate statistics to artificial neural network and random forest regressor (RFR). The RFR model outperformed the other investigated models in terms of R2 (0.14) and RMSE (0.83) for the radon concentration, as a dependent continuous variable. Using IRC discretized into two classes, based on the median (115 Bq/m3), an AUC-ROC value of 0.61 was obtained for logistic regression and 0.62 for the random forest classifier. The presence of cellar beneath the investigated room, the construction period, the height above the sea level or the floor type are the main predictors determined by the models used.

The FIRST large-scale mapping of radon concentration in soil gas and water in Romania.

In the framework of the last Council Directive 2013/59 (Euratom, 2014) laying down basic safety standards for protection against the dangers arising from exposure to ionizing radiation, the problem of radon was assumed in Romania at national level by responsible authorities through the design and development of a National Radon Action Plan and an adequate legislation (HG nr. 526/2018). In order to identify radon risk areas, however, it is necessary to perform systematic radon measurements in different environmental media (soil gas, water, indoor air) and to map the results. This paper presents an atlas of up-to-date radon in soil and water levels for central and western part of Romania. The radon in soil map includes data from 2564 measurements carried out on-site, using Luk3C radon detector. The Luk-VR system was used to measure radon activity concentration from 2452 samples of drinking water. The average radon activity concentration was 29.3 kBq m-3 for soil gas, respectively 9.8 Bq l-1 for water dissolved air. Mapping of radon can be a useful tool to implement radon policies at both the national and local levels, defining priority areas for further study when land-use decisions must be made.

THE CHALLENGE IN USING THE RETROSPECTIVE ASSESSMENT OF RESIDENTIAL RADON CONCENTRATION.

In the present study, the contemporary indoor radon activity concentration and the surface-deposited 210Po activity were measured in 65 Romanian dwellings. The activity of trapped 210Po on the glass surface was measured using the (CR-LR) difference technique. The retrospective radon activity concentration estimated on the basis of age-adjusted 210Po activity was found to have a geometric mean of 318 Bq m-3, being higher than the geometric mean (250 Bq m-3) of the contemporary indoor radon measurements, measured with two types of track detectors (RSKS and Radtrak2®). By applying Lin's concordance correlation coefficient, a substantial strength of agreement (rC = 0.94) was obtained between RSKS and Radtrak2® results, respectively a poor agreement (rC = 0.71) between the retrospective and contemporary methods. The ratio between contemporary and retrospective radon concentrations has a geometric mean of 0.8 and range from 0.2 to 3.9.

DISTRIBUTION OF RADON GAS IN ROMANIAN SHOW CAVES AND RADIATION SAFETY.

In many countries, caves can pose an economic interest for the authorities and stakeholders. The development of a show cave requires, apart from the conservation issues, to ensure the human safety by minimising the exposure to radon for cave personnel and visitors. Radon levels can vary widely from cave to cave, being directly correlated with different internal and external factors. It is therefore important to monitor radon levels before establishing the number of personnel required, so that they are not exposed to health-threatening levels of radiation. A long-term radon survey was carried out for this purpose in five show caves of Romania. The study pointed out the existence of high-radon potential areas inside the caves with concentrations reaching up to 4024 Bqm-3, thus posing radiological hazard to cave personnel and researchers who develop activities underground. Further research focused on personal dosimetry will be necessary for an efficient management of occupational risk.

COMPARATIVE STUDY OF RADON AND THORON MEASUREMENTS IN FOUR ROMANIAN SHOW CAVES.

Measurements have been carried out using four types of passive detectors in four of the most popular show caves in Romania. Three types of detectors (RSKS, RadTrak and CD) were used for radon measurements and two (Raduet and CD) for thoron measurement. Activity concentrations in air were measured in the same locations for two seasons, autumn and winter. Measured values for the different caves varied between below detection limit (5 Bq m-3) and 4024 Bq m-3 for radon and from below 10 to 583 Bq m-3 for thoron. The results indicate a very good correlation between RSKS and RadTrak detectors (r = 0.96). The most significant difference between radon concentrations measured with different types of detectors (RSKS and CD) was higher than 150%. The study suggests that the activity concentration of radon in caves, measured using track detectors, could not be influenced by the type of detector used if the microclimate factor is acknowledged.