Comparison of 222Rn measurement methods in caves

<p>Radon (222Rn) is a naturally inert radioactive gas, originating from the radioactive decay of 226Ra in the 238U radioactive decay chain. 222Rn has a variety of geoscientific applications. 222Rn, however, represents the most significant source of ionizing radiation exposure and can be critical in underground working and living spaces with little or no ventilation. Particularly, caves are recognized as special indoor occupational environments where extremely elevated concentrations of 222Rn may occur during, at least, half-year during its recharged stage.</p><p>The measurement of radon activity concentration in air can be performed using different types of equipment and methodologies. However, it is characterized by the dispersion for relatively short exposition times and depends on the radon activity concentration and environmental parameters. This investigation aims to compare different types of equipment and methodologies to measure 222Rn under real cave conditions.</p><p>Rull Cave is located in Vall d’Ebo, in the south-east of Spain (Alicante province). The host rock of the cave is composed of Miocene conglomerates lying on Cretaceous limestones. Above the cave, the soil has a discontinuous thickness of approximately 1 m. The investigation is performed in winter where the cave remains discharged. During this period, the gas concentration reaches minimum values and presents low fluctuation of radon activity concentration. Temperatures in Rull Cave range between 17 and 20°C, the mean relative humidity reaches about 87%, and the constant pressure of 975 mBar. 222Rn measurements have been taken continually since 2016, ranging from 645 to 3959 Bq/m3.</p><p>We compare, firstly, cave air radon with three devices: AlphaGUARD DF2000, Radim 5WP, and RadonScout Plus. The second method involves the measurement of air radon samples after collecting them in sampling bags. We perform two types of measures: (i) in-situ measures of air samples and (ii) measure of the collected sampling bags 24-hours later (in the laboratory). For this purpose, we use opaque and transparent 1L-gas sampling bags (GSB), and we also evaluate the influence of the air volume (2 or 4 L) on radon activity concentration measurement using AlphaGUARD DF2000 at 0.3 L/min pump flow.</p><p>These findings reveal that i) all devices have similar values of radon activity concentration, with a difference between AlphaGUARD DF2000 with Radim 5WP, and RadonScout Plus of -32% and +19 %, respectively; ii) the use of transparent or opaque GSB provide similar 222Rn concentration; iii) 222Rn concentration after 24-hours is nearly the same than samples tested immediately after collecting; and iv) direct data and the one collected in GSB are equivalent, although 4L GSB often register higher values than 2L. Both methodologies highlight the known problem of radon fluctuations at a short scale. We do recommend collecting air samples in 4L-GSB. It presents practical advantages for cave studies. Thus, 222Rn can be measured in cave areas that are nor not easily accessible areas. In addition, this methodology allows increasing the number of measurements, as well as to safety keep the devices at the lab.</p>

ASSESSMENT OF ANNUAL EFFECTIVE DOSE DUE TO INHALATION AND INGESTION OF RADON IN WATER SAMPLES FROM THE CEMENT INDUSTRIAL AREA OF SOKOTO, NORTH-WESTERN NIGERIA

Water remains the most abundant and critical commodity for guaranteeing the continuity of human lives on earth. Ensuring cleanliness of water for human consumption is of paramount importance. The 222Rn concentration has been assessed in drinking water samples collected from various water resources used by communities around Sokoto Cement Company, with the view of assessing the radiological risk, if any, to human health. The sources of collected water samples were hand pumps and hand dug wells and water seepages. Determination of radon concentration was conducted using liquid scintillation counter (Model: Tri-Carb-LSA1000) following standard procedures. The overall mean value of 222Rn concentration was found to be 34±3.7 Bq/L The resulting mean annual effective doses due to inhalation of radon in the water samples was 41 μSvy-1, while ingestion for adults, children and infants were 248±27 μSvy-1, 372±40 μSvy-1 and 434±47 μSvy-1 respectively. These values are above the recommended benchmarks prescribed by UNSCEAR, WHO, European commission and USEPA guiding the utilization of water for drinking and domestic purposes. This indicates that the water resources around the cement company are not safe for drinking and domestic purposes from the radiological point of view.

Environmental Isotope of Radon-222 for Ciliwung River and Shallow Deep Water Interaction Study

Aquifer in river bank area is mostly susceptive toward pollution occurring in river. One of parameters to determine the interaction process between groundwater and river is a natural isotope of 222Rn. The significant difference of radon concentration in groundwater and river water can be utilized as a scientific basis for investigating groundwater infiltration in river bank. Those studied parameters are residence time and infiltration rate. The research using 222Rn had been conducted in shallow groundwater of Ciliwung river bank - South Jakarta during rainy and dry season. The range of 222Rn concentration in shallow groundwater monitored in dry season was between 666 - 2590 Bq/m3 which was higher than that of rainy season ranging at 440 to 1546 Bq/m3. Otherwise, concentration of 222Rn in river water could not be detected (its 222Rn concentration = 0 Bq/m3) due to its much lower concentration either rainy or dry season. During dry season monitoring, equilibration between groundwater and river water was reached at the distance approximately 98 - 140 m away from river side. Estimating residence time based on 222Rn concentration at nearest site from the river and at equlibration area was 4.2 days such that the infiltration rate from river water into aquifer might be 7.8 m/day.Keywords: 222Rn, groundwater, residence time, infiltration rate.