Radon levels in the volcanic region of La Garrotxa, Spain

Continuous radon monitoring during seven years of volcanic unrest at Campi Flegrei caldera (Italy)

This is a seven-year study (1/7/2011-31/12/2017) of radon monitoring at two sites of Campi Flegrei caldera (Neaples, Southern Italy) that in the last 70 years experienced repeated phases of volcanic unrest. The sites are equipped with devices for radon detection, based on the spectrometry analysis of the α-particles of radon daughters. A hybrid method, as combination of three known methods, is applied for the identification of residuals (anomalies) and trends of the time series of Radon. The results are compared with the following indicators of current caldera unrest: the tremor caused by the major fumarolic vent registered by a seismic station; the cumulative of background seismicity; the maximum vertical deformation acquired by GPS networks during the current phase of uplift; the temperature-pressure of the hydrothermal system estimated based on gas geo-indicators. The comparisons show strong correlation among independent signals and suggest that the extension of the area affected by current Campi Flegrei crisis is larger than the area of seismicity and of intense hydrothermal activity from which the radon stations are 1–4 km away. These results represent an absolute novelty in the study of a such calderic area and mark a significant step forward in the use and interpretation of the radon signal.

Preliminary investigation of 222Rn in the Yakumo Wind-hole, an algific talus deposits, from Izumo, southwest Honshu, Japan

The Yakumo Wind-hole in southwest Japan formed by landslip, and it is known as a cold air blowhole. This wind-hole consists of two parts, which have complementary relationships in regard to the flow of air, namely, topographically upper and lower holes that can be characterized as a warm wind-hole (WWH) and cold wind-hole (CWH), respectively. We carried out a preliminary investigation of radon behavior in the Yakumo Wind-hole. The data showed remarkable seasonal change from high ²²²Rn concentrations reaching to 7.6 ± 0.1 kBq/m³ in the warm season (mid-May to October) to low ²²²Rn concentrations in the cold season (December to early May) at the CWH. The threshold in the regional atmospheric temperature was estimated as 16.2 °C for the beginning and 17.1 °C for the ending periods of air blow with higher ²²²Rn concentrations. These seasonal changes in ²²²Rn were not only associated with the dynamic convection caused by temperature differences in and out of the talus, but were also related to the relative humidity of air that is blown out. High ²²²Rn concentrations were formed in the high humidity environment, and the humidity may possibly be associated with melting ice. According to the known information on ²²²Rn behavior in relation to humidity, a radon trap in the growing ice in spring and in the melted water in summer are suggested. This study revealed that ²²²Rn measurements are a useful tool to understand the air dynamics in the talus.

Characterization of radon levels in soil and groundwater in the North Maladeta Fault area (Central Pyrenees) and their effects on indoor radon concentration in a thermal spa

Radon levels in the soil and groundwater in the North Maladeta Fault area (located in the Aran Valley sector, Central Pyrenees) are analysed from both geological and radiation protection perspectives. This area is characterized by the presence of two important normal faults: the North Maladeta fault (NMF) and the Tredós Fault (TF). Two primary aspects make this study interesting: (i) the NMF shows geomorphic evidence of neotectonic activity and (ii) the presence of a thermal spa, Banhs de Tredós, which exploits one of the several natural springs of the area and needs to be evaluated for radiation dosing from radon according to the European regulation on basic safety standards for protection against ionizing radiation. The average soil radon and thoron concentrations along a profile perpendicular to the two normal faults - 22 ± 3 kBq·m^-3 and 34 ± 3 kBq·m^-3, respectively - are not high and can be compared to the radionuclide content of the granitic rocks of the area, 25 ± 4 Bq·kg^-1 for ²²⁶Ra and 38 ± 2 Bq·kg^-1 for ²²⁴Ra. However, the hypothesis that the normal faults are still active is supported by the presence of anomalies in both the soil radon and thoron levels that are unlikely to be of local origin together with the presence of similar anomalies in CO₂ fluxes and the fact that the highest groundwater radon values are located close to the normal faults. Additionally, groundwater ²²²Rn data have complemented the hydrochemistry data, enabling researchers to better distinguish between water pathways in the granitic and non-granitic aquifers. Indoor radon levels in the spa vary within a wide range, [7-1664] Bq·m^-3 because the groundwater used in the treatment rooms is the primary source of radon in the air. Tap water radon levels inside the spa present an average value of 50 ± 8 kBq·m^-3, which does not exceed the level stipulated by the Spanish Nuclear Safety Council (CSN) of 100 kBq·m^-3 for water used for human consumption. This finding implies that even relatively low radon concentration values in water can constitute a relevant indoor radon source when the transfer from water to indoor air is efficient. The estimated effective dose range of values for a spa worker due to radon inhalation is [1-9] mSv·y^-1. The use of annual averaged radon concentration values may significantly underestimate the dose in these situations; therefore, a detailed dynamic study must be performed by considering the time that the workers spend in the spa.

Soil radon dynamics in the Amer fault zone: An example of very high seasonal variations

Soil radon levels of the Amer fault zone have been measured for a 4 year-period with the aim of checking seasonal fluctuations obtained in previous studies and to understand radon origin and dynamics. In this manuscript additional results are presented: updated continuous and integrated soil radon measurements, radionuclide content of soil materials and a detailed analysis of an urban profile by means of the electrical resistivity imaging technique and punctual soil radon, thoron and CO2 measurements. Integrated and continuous measurements present a wide range of values, [0.2-151.6] kBq m(-3) for radon, [4.5-39.6] kBq m(-3) for thoron and [4.0-71.2] g m(-2) day(-1) for CO2. The highest soil radon levels in the vicinity of the Amer fault (>40 kBq m(-3)) are found close to the fractured areas and present very important fluctuations repeated every year, with values in summer much higher than in winter, confirming previous studies. The highest radon values, up to 150 kBq m(-3), do not have a local origin because the mean value of radium concentration in this soil (19 ± 5 Bq kg(-1)) could not explain these values. Then soil radon migration through the fractures, influenced by atmospheric parameters, is assumed to account for such a high seasonal fluctuation. As main conclusion, in fractured areas, seasonal variations of soil radon concentration can be very important even in places where average soil radon concentration and radium content are not especially high. In these cases the migration capability of the soil is given not by intrinsic permeability but by the fracture structure. Potential risk estimation based on soil radon concentration and intrinsic permeability must be complemented with geological information in fractured systems.

Radon levels in groundwaters and natural radioactivity in soils of the volcanic region of La Garrotxa, Spain

Groundwater radon level and soil radionuclide concentration have been measured in the volcanic region of La Garrotxa (Catalonia, Spain) to further research on the origin and dynamics of high radon levels over volcanic materials found in this region. Water samples from different aquifers have been collected from wells and springs and the water radon levels obtained have been lower than 30 Bq l(-1). Soil samples have been collected from different geological formations (volcanic and non-volcanic), being Quaternary sedimentary deposits those that have presented the highest mean values of (40)K, (226)Ra and (232)Th concentrations (448 ± 70 Bq kg(-1), 35 ± 5 Bq kg(-1) and 38 ± 5 Bq kg(-1), respectively). Additionally, indoor/outdoor terrestrial radiation absorbed dose rate in air have been measured to better characterize the region from the radiological point of view. Terrestrial radiation absorbed dose rates measurement points have been chosen on the basis of geological and demographical considerations and the results obtained, from 27 to 91 nGy h(-1), show a clear relation with geological formation materials. The highest terrestrial gamma absorbed dose rate is observed over Quaternary sedimentary deposits as well. All these results help to better understand previous surveys related with indoor and outdoor radon levels and to reinforce the hypotheses of a radon transport through the fissure network.