GI6.7

Exposure to indoor radon (Rn) is recognized as a health hazard which may cause several 100,000 lung cancer fatalities per year world-wide. Physical causes are Rn generation as part of the decay chains that originate in ubiquitous uranium and thorium and its transport through the natural to the built environment, where it can infiltrate indoor air. Generation and transport of Rn constitute geogenic Rn hazard. Its geographical distribution reflects the ones of the properties of the media in which the processes occur, namely their geochemistry and physical properties such as porosity, permeability and humidity. By linking to measured indoor Rn concentration, geogenic hazard can be transformed into the expected indoor Rn concentration in a hypothetical house at a location or the probability that in the house a Rn threshold is exceeded.

Hazard turns into risk if somebody is exposed to the hazardous agent. Given a certain amount of hazard, the risk results from conditions which enable exposure (defining vulnerability and susceptibility to the hazard) and the presence of people who are actually exposed. While hazard yields a probability that somebody exposed suffers a detriment, risk quantifies the size of the detriment, e.g. the expected number of Rn induced lung cancer fatalities per unit area. Elevated risk can occur also if the individual probability of detriment is low, if the number of exposed persons is high.

Rn abatement policy which through regulation aims to reduce the detriment, should respond differently to hazard and risk. In the former case, it should reduce the probability of individual high exposure occurring, by remediation, or avoiding it to occur, by preventive action. Responding to the latter means reducing collective exposure.

So far, policy has mainly focused on the first, i.e. hazard reduction, while comparatively less attention has been given to the second, although the overall detriment to society depends on it. Although Rn regulation has already been developed extensively in Europe, discussion of the aspect of collective risk reduction seems to be in the beginning only.

In this presentation, we outline the problem by showing the difference between hazard and risk and addressing existing Rn abatement strategies.

How to cite: Bossew, P. and Petermann, E.: Radon hazard vs. radon risk – consequences for radon abatement policy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3145, https://doi.org/10.5194/egusphere-egu22-3145, 2022.

Radon and its progeny are well-documented sources of natural radioactivity which can be used as benchmarks for testing a novel ionisation detector. The miniaturised ionisation detector was deployed aboard the NRP Sagres on a SAIL mission in July 2021 which travelled between the Açores and Lisbon in the North Atlantic Ocean. On its voyage, the detector profiled natural background radiation and in-directly detected cosmic ray muons, providing both spectroscopic energy discrimination and count rate data. The detector was simultaneously run with a NaI(Tl) gamma ray counter and other meteorological instruments.

The small form factor and low-power detector, composed of a 1x1x0.8 cm³ CsI(Tl) microscintillator coupled to a PiN photodiode, was able to identify gamma peaks from Bi-214 and K-40, having been calibrated using laboratory gamma sources up to 1.3 MeV. This research aims to investigate the performance of the ionisation detector and behaviour of discrete gamma energies over the duration of the voyage. Additionally, we will show a comparison of the CsI(Tl) based ionisation detector against the gamma ray counter which features a larger NaI(Tl) scintillator.

How to cite: Tabbett, J., Aplin, K., and Barbosa, S.: Measuring Background Radiation with a Novel Ionisation Detector Aboard A North Atlantic Voyage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4833, https://doi.org/10.5194/egusphere-egu22-4833, 2022.

In the framework of the EMPIR project 19ENV01 traceRadon⁽¹⁾ [1] stable atmospheres with low-level, activity concentrations of radon have to be produced for the calibration of radon detectors [2] capable of measuring the outdoor air activity concentration. The traceable calibration of these detectors at very low activity concentrations is of special interest, for the radiation protection community, as well as the climate observation community. Because radiation protection networks (like the EUropean Radiological Data Exchange Platform (EURDEP)) and climate observation networks (like the Integrated Carbon Observation System (ICOS)) need reliable, accurate radon activity concentration measurements, either for identification of Radon Priority Areas (RPA), for false alarm prevention or to apply the Radon Tracer Method (RTM) for the estimation of greenhouse gas (GHG) emissions.

Radon gas is the largest source of public exposure to naturally occurring radioactivity, and concentration maps based on atmospheric measurements aid developers to comply with EU Safety Standard Regulations. Radon can also be used as a tracer to evaluate dispersal models important for supporting successful greenhouse gas (GHG) mitigation strategies. One of the recently most applied technique for this propose is the Radon Tracer Method (RTM). To reduce the uncertainty of both radiation protection measurements and those used for GHG modelling, traceability to SI units for radon exhalation rate from soil, its concentration in the atmosphere and validated models for its dispersal are needed. The project traceRadon started in 2020 to provide the necessary measurement infrastructure [3,4]. This is particularly important for GHG emission estimates that support national reporting under the Paris Agreement on climate change.

As there is an overlapping need between the climate research and radiation protection communities for improved traceability at low-level outdoor radon and radon flux measurements the project traceRadon works on this aspect for the benefit of two large scientific communities.  The results at midterm of the project are presented.

[1] Röttger, A. et al: New metrology for radon at the environmental level 2021 Meas. Sci. Technol. 32, 124008, https://doi.org/10.1088/1361-6501/ac298d

[2] Radulescu, I et al.: Inter-comparison of commercial continuous radon monitors responses, Nuclear Instruments and Methods in Physics Research Section A, Volume 1021, 2022, 165927, https://doi.org/10.1016/j.nima.2021.165927

[3] Mertes, F et. al.: Approximate sequential Bayesian filtering to estimate Rn-222 emanation from Ra-226 sources from spectra, https://doi.org/10.5162/SMSI2021/D3.3

[4] Mertes, F. et. al.: Ion implantation of ²²⁶Ra for a primary ²²²Rn emanation standard, Applied Radiation and Isotopes, Volume 181, March 2022, 110093, https://doi.org/10.1016/j.apradiso.2021.110093

How to cite: Röttger, S., Röttger, A., Grossi, C., Karstens, U., Cinelli, G., and Rennick, C.: New traceability chains for the measurement of radon at the environmental level, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3966, https://doi.org/10.5194/egusphere-egu22-3966, 2022.

Radon (²²²Rn, t _1/2 = 3.82 days) is by far the dominant radionuclide in indoor air and constitutes a health hazard in poorly ventilated environments, such as caves, mines or tunnels. In these contexts, radon gas can accumulate, reaching harmful concentrations due to the ionizing radiation from ²²²Rn and its progeny. To minimize the exposure risk, a radon monitoring program is required to adopt mitigation measures for the radiological protection of workers, cavers and visitors. The Directive 2013/59/EURATOM sets the recommended occupational and public effective dose limits being 20 and 1 mSv/year, respectively.

El Viento Cave is a volcanic lava tube located in the northern flank of Pico-Viejo volcano, in the Icod Valley, (Tenerife, Canary Islands, Spain). It was formed during the early eruptions of the Pico Viejo volcano, 27,030 ± 430 years ago, from basaltic, plagioclase-rich pahoehoe lavas. The cave has an extraordinary complexity, with several sinuous tubes and branches in three superimposed and interconnected levels and is considered the 5^th longest volcanic cavity on Earth (Carracedo and Troll, 2013). A 200 m long segment of this lava tube, named “El Sobrado Cave”, is enabled for touristic visits. Only in 2019 the cave received more than 28000 visitors.

Monthly radon profiles were obtained during one year (from 2020/10/01 to 2021/09/30) in the touristic section of the cave by using SSNTD (CR-39), installed approximately every 35 m. Besides, a RadonScout monitor (SARAD GmbH) was set up at about 100 m from the cave entrance, for continuous monitoring (integration time of 1 hour) of radon and environmental parameters (air temperature, relative humidity, and barometric pressure).

²²²Rn levels inside the cave ranged from 0-5.000 Bq/m³, exhibiting seasonal, diurnal and semidiurnal fluctuations. Short-period radon variations (24 and 12 h frequencies) are related to air temperature and humidity. Long-period radon fluctuations (annual-seasonal) are correlated with rainfall, with lower radon levels in winter (rainy season) and higher in summer (dry season).

Annual mean effective dose due to ²²²Rn gas exposure was estimated from the geometric mean of radon concentration during the studied period, assuming an average indoor occupancy of 10 working hours/week during 48 weeks/year for guides and a punctual visit of 1 hour for tourists. In these conditions, the resulting annual effective dose computed for guides is below 2mSv/year.

References:

Carracedo, J.C. & Troll, V.R. (Eds.). (2013). Teide Volcano: Geology and Eruptions of a Highly Differentiated Oceanic Stratovolcano. Active Volcanoes of the World, Springer Berlin Heidelberg, 296 pp.

How to cite: Martín-Luis, M. C., Salazar-Carballo, P. A., López-Pérez, M., Duarte-Rodríguez, X., and Martín González, M. E.: Radon monitoring in a volcanic cave: El Viento Cave (Canary Islands, Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-775, https://doi.org/10.5194/egusphere-egu22-775, 2022.

Groundwater age can differ when determined by radioactive tracers due to different retardation factors. According to Krishnawami et al. 1982, Radon isotopes supply to groundwater is considered as a measure of the supply of Radium isotopes. This assumption considerably affects the estimation of the Ra retardation factor. Briganti et al. 2020 reports how the different groundwater supply mechanisms of Ra and Rn should be considered in order to avoid a relevant variation between the real water residence time and the age calculated. In the same work an alternative method for estimating Ra retardation factor is proposed without using Rn data as a comparison term. A synthesis of the main results of laboratory tests is presented in order to describe possible applications of the method.

References

Briganti A., Voltaggio M., Tuccimei P. & Soligo M. 2020. Radium in groundwater hosted in porous aquifers: estimation of retardation factor and recoil rate constant by using NAPLs. SN Appl. Sci. 2, 1934 (2020). https://doi.org/10.1007/s42452-020-03610-4

Krishnaswami S., Graustein W.S., Turekian K.K., Dowd J.F. 1982. Radium, thorium and radioactive lead isotopes in groundwaters: application to the in situ determination of adsorption-desorption rate constants and retardation factors. Water Resour. Res. 18:1633–1675.

How to cite: Briganti, A., Voltaggio, M., Tuccimei, P., and Soligo, M.: Residence time of groundwater in porous aquifers by estimating Ra retardation factor, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13477, https://doi.org/10.5194/egusphere-egu22-13477, 2022.

As groundwater is an important source of drinking water, its quality is of great importance. In recent years, following the EU regulations, radioactivity parameters are also included among the quality measures. 

In the area of the city Sopron (Hungary), groundwater resources are used for drinking water supply. The area had been actively researched for fissile materials, and previous studies measured high radon activity for example in the geophysical observatory (500–1000 kBq m^–3)  and in natural springs (up to 220 Bq L^–1).

Natural springs bear important information about their parent flow systems, about the transit time and the rock-water interactions along the flow paths. The aim of the study was to investigate the natural springs of the Sopron Mountains and to measure not only the physico-chemical properties (discharge rate, pH, electrical conductivity, temperature, dissolved oxygen content, redox potential, major ion content), but also to determine the uranium, radium and radon activity concentration of the springwaters. 

The measurements revealed low discharge rate (< 5 L min^–1), low dissolved solid content (< 450 mg L^–1 TDS) and temperature (10–12°C) for the majority of the springs, which indicate that the waters travel in the subsurface along local flow systems. Two springs, which are situated in the foothills, i.e. at lower elevation, show higher dissolved solid content (1115 mg L^–1, 481 mg L^–1) and higher temperature (15.6°C, 16°C). Their uranium content was also higher, 86–93 mBq L^–1. In the case of these springs, the physico-chemical parameters suggest longer travel time, i.e. more time for rock-water interactions which is reflected in their higher dissolved solid and uranium content.

Radon exceeding the 100 Bq L^–1 activity concentration was measured in two springs. For the other springs, the radon concentrations were 2-79 Bq L^-1.

As all the springs are situated in the regional recharge area of groundwater resources of the area, the study delivered important information regarding the rock-water interactions and the improvement of groundwater quality during subsurface reactions.

How to cite: Molnár, B., Baják, P., Csondor, K., Jobbágy, V., Izsák, B., Vargha, M., Pándics, T., Horváth, Á., and Erőss, A.: Natural radioactivity and rock-water interactions in the springs of Sopron Mountains (Hungary), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10471, https://doi.org/10.5194/egusphere-egu22-10471, 2022.

Artificial radionuclides emitted into the environment have become tools to understand the physical processes in the last half-century and model future geophysical phenomena. In the case of a high contamination event such as a nuclear accident, it is challenging to capture the three-dimensional subsurface migration behavior of radionuclides during the most dynamic and crucial period shortly after the initial fallout because of the risk to human observers. Thus, geophysical models often rely on stabilized radionuclides, hypothesizing the radionuclide mobility in the initial phase. This study aims to demonstrate the rapid changes of vertical profiles of Cs-137 in short years after initial depositions, using soil samples collected in a forest and on abandoned farmland in Fukushima, Japan, five to seven years after the Fukushima Daiichi Nuclear Power Plant Accident in 2011.

The subsurface migration profiles, including the actual migration head depth of Cs-137, were examined against local topographic indices. Some of the preliminary results show that actual subsurface migration of the FDNPP-derived Cs-137 was equal to or deeper than 30 cm depth in nine forest soil samples; the confirmed deepest migration was at 38 cm. Meanwhile, the actual migration depths in abandoned crop fields were less than 15 cm. Along a 500 m hillslope, deposition was observed at five locations. The interaction of the timing of deposition and erosion depths was deciphered from Cs-137 vertical profiles and surrounding topography. The findings from this study demonstrate the implications of radionuclides behavior during a dynamic migration period to natural and artificial environmental radioactivity analysis. To accurately estimate the activities of radionuclides years later, these initial losses and gains of target radionuclides in the soil need to be considered with temporal progress, along with nuclear decay.

How to cite: Yasumiishi, M. and Nishimura, T.: Learning from subsurface migration profiles of an artificial radionuclide during a volatile migration period, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10082, https://doi.org/10.5194/egusphere-egu22-10082, 2022.

Uranium mining legacies still pose a significant risk to human health and the environment in certain Central Asian regions. Drone-based methods are well-suited for mapping radionuclides of contaminated sites and for planning, monitoring and quality assurance of remediation measures. In the DUB-GEM project (Development of a UAV-based Gamma spectrometry for the Exploration and Monitoring of Uranium Mining Legacies), which is funded by the Federal Ministry of Education and Research (BMBF), a German interdisciplinary consortium led by the Federal Institute for Geosciences and Natural Resources (BGR) is developing a drone-based detector system for the investigation of contaminated uranium mining and processing legacy sites. The project is co-funded by the Coordination Group for Uranium Legacy Sites (CGULS) program of the International Atomic Energy Agency (IAEA). CGULS coordinates cooperation among IAEA Member States affected by ULS and national and international organizations involved in the management, remediation, or regulatory oversight of ULS. CGULS supports the Central Asian partner countries of DUB-GEM to participate in activities of the DUB-GEM consortium.

The applicability of the system is to be tested in the DUB-GEM partner countries Kyrgyzstan, Kazakhstan, Uzbekistan and Tajikistan. Some of the uranium legacy sites (ULS) in Central Asia, especially those in Kyrgyzstan, are difficult to access due to the mountainous topography. Once fully developed, the system will allow the efficient and safe mapping and monitoring of radioactive contamination at such sites without requiring experts to trek through difficult terrain with heavy equipment, exposing themselves to potential physical and radiological risks.

As part of the DUB-GEM project, two specially designed scintillation detectors were used, each of which can be mounted on the heavy-lift drone which was also custom-built for the project and has a maximum take-off mass (MTOM) of 25 kg. The drone-based gamma spectrometry system was successfully tested at different sites in Germany in autumn 2020 and late summer 2021. In autumn 2021, the system was tested for the first time in Kyrgyzstan (Mailuu Suu) and Kazakhstan (Muzbel’). Despite the technical and logistical challenges, drone surveys with the gamma spectrometers could be flown at three sites. The count rates of the detectors were transmitted in real time to a ground station so that hotspots could be detected during flight.

The resulting maps presented here show the distributions of dose rates and radionuclides of the uranium-238 series, thorium-232 series and potassium-40. Comparison with samples from the ground was used to calibrate the instruments.

The extensive data sets from both detectors offer a multitude of further evaluation possibilities, which are currently being evaluated.

A further airborne survey campaign in Central Asia is planned for late summer 2022 to map legacies in Uzbekistan.

How to cite: Preugschat, B., Ibs-von Seht, M., Kunze, C., Arndt, R., Kandzia, F., Wiens, B., Altfelder, S., and Walther, C.: Drone-Based Investigation of Uranium Mining Legacies – Recent Developments in the DUB-GEM Project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12872, https://doi.org/10.5194/egusphere-egu22-12872, 2022.

Depending on their concentration, naturally occurring radioactive materials (NORM) used for the construction of walls in living rooms may contribute elevated levels of radiation exposure for inhabitants. The main path of exposure by building materials is thought to be due to gamma radiation of ⁴⁰K and the progenies of the ²³⁸U and ²³²Th decay chains. Many efforts have been focused on developing computational methodologies to evaluate and predict the indoor gamma dose rate. Those studies investigated factors such as concrete density or wall thickness of the material as well as factors relating to the dimensions of the room with respect to gamma ray exposure.

Here, we re-implemented a well-established room model (Mustonen, 1984). This model approximates the gamma ray exposure at any point in a model room by accounting for the source strength, radiation absorption by concrete including build-up factors and the 1/r² decrease due to the distance to the source. The results of our re-implemented model compare well with other models, which focus on the radiation exposure in the midpoint of the room. In addition to concrete density and wall thickness, we focus our investigation on a non-homogenous distribution of NORM in walls, ceiling and floors. We compare different configurations of NORM distributions with respect to the radiation exposure in the room centre and with the average received within the room at a height of 1.25m.

References:

Mustonen, R. (1984). Methods for evaluation of radiation from building materials. Radiation Protection Dosimetry 7, 235-238.

How to cite: Fohlmeister, J. and Hoffmann, B.: Investigating a redistribution of naturally occurring radioactive material (NORM) in dwelling walls, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13202, https://doi.org/10.5194/egusphere-egu22-13202, 2022.