Effectiveness Analysis of Filters Used with Radon Detectors under Extreme Environmental Conditions for Long-term Exposures

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.

Continuous monitoring of radon gas as a tool to understand air dynamics in the cave of Altamira (Cantabria, Spain)

The use of radon as an atmospheric tracer in the Altamira Cave over the past 30years has provided relevant information about gaseous exchanges between the Polychromes Room, the adjoining Chambers inside the cave, and the outside atmosphere. The relatively simple physico-chemical behaviour of radon gas provides a marked advantage over other tracer gases that are usually present in high concentrations in hypogeous environments, such as CO₂. Two types of continuous radon measurement were undertaken. The first involves active detectors located in the Hall and Polychromes Room, which provide radon concentration values at 1-hour intervals. In addition, nuclear solid track etched detectors (CR-39) are used in every chamber of the cave over 14-day exposure periods, providing average radon concentrations. In this paper we show some of the specific degassing and recharge events identified by anomalous variations in the concentration of radon gas in the Polychromes Room. In addition, we update knowledge regarding the degree of connection between chambers inside the cave and with the outside atmosphere. We verify that the connection between the Polychromes Room and the rest of the cave has been drastically reduced by the installation of the second closure in 2008. Except for point exchanges with the Crossing zone generated by a negative temperature gradient in that direction, the atmosphere of the Polychromes Room remains stable, or else it exchanges matter with the outside atmosphere through the karst interface. The role of radon as a tracer is demonstrated to be valid both to reflect seasonal cycles of degassing and recharge, and to analyse shorter (daily) period fluctuations.

Dose assessment to workers in a dicalcium phosphate production plant

The production of dicalcium phosphate (DCP) uses phosphate rock (PR) as a raw material. Sedimentary phosphate rocks are enriched with relevant concentrations of natural radionuclides from the ²³⁸U decay chain (around 10³ Bq·kg^-1), leading to the need of controlling potential exposures to radiation of workers and members of the public in accordance with IAEA safety standards. Indeed, phosphate industries are classified as Naturally Occurring Radioactive Material (NORM) industries. Thus, the aim of this work is to assess the radiological risk of the workers in a DCP production plant located in the Iberian Peninsula (South-West Europe), which digests PR with hydrochloric acid. In the present study ²³⁸U, ²³⁰Th, ²²²Rn, ²¹⁰Pb and ²¹⁰Po concentrations in aerosols (indoor and outdoor areas) are reported. Aerosols showed concentrations between 0.42-92 mBq·m^-3 for ²³⁸U, 0.24-33 mBq·m^-3 for ²³⁰Th, 0.67-147 mBq·m^-3 for ²¹⁰Pb and 0.09-34 mBq·m^-3 for ²¹⁰Po. Long-term exposure (four months) of passive ²²²Rn detectors provided concentrations that ranged from detection limit (< DL) to 121 Bq·m^-3 in outdoor areas and from < DL to 211 Bq·m^-3 in indoor areas, similar to concentrations obtained from short-term measurements with active detectors from < DL to 117 Bq·m^-3 in outdoor areas and from < DL to 318 Bq·m^-3 in indoor places. ²²⁶Ra accumulation in ebonite and pipe scales were the most important contributions to the ambient dose equivalent H*(10), resulting in 0.07 (background)-27 μSv·h^-1 with a median value of 1.1 μSv·h^-1. Average ²²²Rn air concentrations were lower than the 300 Bq·m^-3 limit and therefore, according to European Directive 2013/59/EURATOM, ²²²Rn concentration is excluded from the worker operational annual effective dose. Thus, considering the inhalation of aerosols and the external dose sources, the total effective dose determined for plant operators was 0.37 mSv·y^-1.