GI6.2

Ambient radioactivity reflects a wide range of physical processes, including atmospheric and geological processes, as well as space weather and solar conditions. Gamma radiation near the Earth’s surface comes from diverse sources, including space (cosmic radiation), the earth’s atmosphere, and solid earth. In addition to the terrestrial gamma radiation originating from the radioactive decay of primordial radionuclides present in every soil and rock, gamma radiation is also continuously produced in the atmosphere from the interaction of secondary cosmic rays and upper-atmosphere gases, as well as from the decay of airborne radon (Rn-222) progeny. Therefore the temporal variability of gamma radiation contains information on a wide range of physical processes and space-earth interactions, but disentangling the different contributions remains a challenging endeavor. Continuous monitoring of gamma radiation at sea enables to remove both the terrestrial and radon exhalation contributions, allowing to examine in detail the space and atmospheric sources of ambient gamma radiation.

Gamma radiation over the Atlantic Ocean was measured on board the ship-rigged sailing ship NRP Sagres in the framework of the SAIL (Space-Atmosphere-Ocean Interactions in the marine boundary Layer) project. The measurements were performed continuously (every 1-second) with a NaI(Tl) scintillator counting all the gamma rays from 475 keV to 3 MeV. The casing of the instrument was adapted in order to endure the harsh oceanic conditions and installed in the mizzen mast of the ship. The counts were linked to a rigorous temporal reference frame and precise positioning through GNSS.

Here preliminary results based on the gamma radiation measurements performed from January 5^th to May 9^th 2020 are presented, corresponding to the journey of the ship from Lisboa to Cabo Verde, Rio de Janeiro, Montevideu, Cape Town, and back to Lisboa. The data exhibit a clear transition from the coastal to the marine environment, enabling to study in detail the temporal variation of gamma radiation in the marine boundary layer, as well as the interface between land and marine conditions in terms of environmental radioactivity.

How to cite: Barbosa, S., Amaral, G., Almeida, C., Dias, N., Ferreira, A., Camilo, M., and Silva, E.: Environmental radioactivity in the Atlantic marine boundary layer from the SAIL monitoring campaign , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1264, https://doi.org/10.5194/egusphere-egu21-1264, 2021.

Radioactivity soundings have been performed in Finland since the early 1960s to measure radiation and radioactivity levels in the atmosphere up to the height of 40 km.  A sonde package based on a Geiger-Müller (GM) tube is carried up to the stratosphere by a balloon filled with hydrogen or helium. En route the GM tube count rate values are sent to the ground station with a radio transmitter.

Vaisala Corporation developed a radioactivity sounding system in the early 1960s. Radioactivity soundings were performed at the company's aerological test station in Helsinki as a part of development and quality assurance activities. At least once, in October 1962, these radioactivity soundings revealed the presence of abnormal radioactivity in the stratosphere over Finland due to atmospheric nuclear tests.

The Finnish Defence Forces acquired the Vaisala's radioactivity sounding system in 1963. This system was placed at the Finnish Meteorological Institute's (FMI) meteorological observatory of Jokioinen. The staff of the observatory operated the system. Initially radioactivity soundings were performed once a week but later sparser and sparser so that in 1980 only one sounding, in November after the so far last atmospheric nuclear test, was performed. Only a couple of publications have been produced from the artificial radioactivity observations in the upper atmosphere, perhaps due to the sensitive nature of the subject. After 1980 no more radioactivity soundings were performed in Finland during the 1980s, not even during the 1986 Chernobyl accident.

In the aftermath of the Chernobyl accident Vaisala developed a new generation of radioactivity sondes that are incorporated into the company's meteorological sounding systems. The FMI has performed these radioactivity soundings since the early 1990s at its sounding stations at Jokioinen, Tikkakoski and Sodankylä. Usually one or two soundings are performed per year, often during nuclear accident preparedness exercises.

The radioactivity soundings described above have brought information on cosmic radiation even if the main motivation was the surveillance of artificial radioactivity in the upper atmosphere. However, balloon soundings dedicated to cosmic radiation research have been made by the University of Oulu. These sounding activities were coordinated by SPARMO organization (Solar Particles and Radiation Monitoring Organization), later with the name SBARMO (Scientific Ballooning and Radiation Monitoring Organization). Altogether 114 soundings were performed from 1965 to 1979. In addition to scientific results these activities helped the then new university to network with the international scientific community.

Balloon-borne radiation sondes have shown to be a flexible and a cost-efficient method to obtain data on the radiation environment of the upper atmosphere. The information about the vertical distribution of a radioactive plume provided by soundings is essential for a reliable atmospheric dispersion estimation. This, in turn, helps to plan and execute protective measures, e.g. stable iodine prophylaxis. On the other hand, the altitude information about observed airborne radioactivity of unknown origin benefits the inverse modeling to find out the possible source areas of the release. This can be useful for example in detecting clandestine nuclear activities.

How to cite: Paatero, J., Hatakka, J., Kivi, R., and Immonen, J.: Radioactivity soundings of the upper atmosphere in Finland 1962-2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11452, https://doi.org/10.5194/egusphere-egu21-11452, 2021.

The SMEAR Estonia station (58.277663 N, 27.308266 E, 36 m a.s.l.) was established in south-east of Estonia at the Järvselja Experimental Forestry in 2012 to investigate the atmosphere-biosphere interactions and atmospheric aerosol formation and growth.

In summer 2019, the gamma-radiation monitor GammaTRACER XL2-3 (Saphymo GmbH) was set up at Järvselja station and the rain sensor DRD11A (Vaisala Oyj) in autumn 2019. These devices enable to measure the gamma-radiation dose rate and precipitation intensity, which affect the ionization rate of atmospheric air close to ground, with high accuracy and time resolution, and complement our measurement system of atmospheric ions and aerosol particles.

The gamma-radiation dose rate measurements at about 1.2 m above the ground reveled on relatively steady background about 70 nSv/h occasional events with increase up to about 110 nSv/h, which correlated well with rainfall intensity. Commonly such events last 3-4 hours, but in specific meteorological situation with continuous long-lasting rain and air mass movement from southerly directions the effect can last 2-3 days, resulting in gradual increase in gamma-radiation dose rate level during about 24 h.

Such a phenomenon is known to occur due to wet deposition of radioactive aerosol particles during rain, namely due to the radon (²²² Rn) short-lived daughter progeny products (Po-218, Pb-214, Bi-214) attached to atmospheric aerosol particles. The radon (²²² Rn) daughter progeny involvement is confirmed by simultaneous gamma-spectrometric measurements with SARA AGS711F (Envinet GmbH) at Tõravere station (58° 15' 52,9" N, 26° 27' 42,1", 72 m), located about 50.3 km west from the Järvselja SMEAR station. The gamma dose rates showed very similar temporal behavior when both stations were affected by the same air mass with precipitation zone passing over the stations.

To our best knowledge, the details of rain-induced enhancement of gamma-radiation dose rate and atmospheric processes behind the phenomenon are not well known and are worth future investigations. The events of rain induced gamma-radiation dose rate enhancement at Järvselja SMEAR and Tõravere station are analyzed and discussed in more detail in the presentation and the spatial representativity of the phenomenon is estimated based on the gamma-radiation monitoring network data of Estonian Early Warning System.

How to cite: Hõrrak, U., Chen, X., Hõrrak, K., Rand, U., Komsaare, K., Vana, M., Luts, A., and Junninen, H.: The rain induced gamma-radiation dose rate enhancement at Järvselja SMEAR station, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15644, https://doi.org/10.5194/egusphere-egu21-15644, 2021.

Air ions are ubiquitous in the atmosphere. These charge carriers can be found in various forms as charged molecules, nanoclusters as well as aerosol particles. The population of air ions normally concentrates in the cluster size range (0.8 – 1.7 nm in mobility equivalent diameters) in the absence of particle formation processes. A concentration burst in the intermediate size range (1.7 – 7 nm) can be typically observed during atmospheric new particle formation (NPF) and in precipitation episodes ¹. Contrary to the intermediate ions formed during NPF that favour growth to larger sizes, intermediate ion bursts resulting from precipitation tend to shrink ^2,3. The production of intermediate ions during precipitation has been attributed to the Lenard effect and they are usually referred to as the balloelectric ions ³.

During precipitation the rain-out and wash-out of radon progeny increase the gamma dose at ground level ⁴. Being a type of ionising radiation, gamma creates positive and negative charges in the air. These charges are either lost in recombination or transformed into air ions. It is therefore interesting to understand whether the precipitation-associated elevation in gamma radiation plays any role in forming or neutralising the balloelectric ions. At SMEAR II station in Hyytiälä, Finland ⁵, we have conducted measurements of air ions, gamma radiation, precipitation together with other meteorological parameters. A similar establishment of the measurement set stands also at SMEAR Estonia station in Jarvseljä, Estonia ⁶. The data collected at Hyytiälä from 2017.7 to 2018.8 show that the intermediate ion concentration correlates with rainfall only when the precipitation intensity is greater than 1 mm/h. For milder rainfall with the precipitation intensity being 0.1-1 mm/h, the intermediate ion concentration increases with an increase in the gamma counts. The work is under progress and we intend to extend the analysis to Jarvseljä data for a comprehensive understanding of the observations.

Acknowledgements: This work received financial supports from European Regional Development Fund (project MOBTT42) under the Mobilitas Pluss programme and from Estonian Research Council project PRG714.

References:

1. Tammet, H., Komsaare, K. & Hõrrak, U. Intermediate ions in the atmosphere. Atmospheric Research 135-136, 263-273, doi:10.1016/j.atmosres.2012.09.009 (2014).

2. Hõrrak, U. et al. Formation of Charged Nanometer Aerosol Particles Associated with Rainfall: Atmospheric Measurements and Lab Experiment. Report Series in Aerosol Science 80, 180-185 (2006).

3. Tammet, H., Hõrrak, U. & Kulmala, M. Negatively charged nanoparticles produced by splashing of water. Atmos. Chem. Phys. 9, 357–367 (2009).

4. Paatero, J. & Hatakka, J. Wet deposition efficiency of short-lived radon-222 progeny in central Finland. Boreal Env. Res. 4, 285-293 (1999).

5. Hari, P. & Kulmala, M. Station for measuring ecosystem-atmosphere relations (SMEAR II). Boreal Environ. Res. 10, 315-322 (2005).

6. Noe, S. M. et al. SMEAR Estonia: Perspectives of a large-scale forest ecosystem – atmosphere research infrastructure. Forestry Studies 63, doi:10.1515/fsmu-2015-0009 (2015).

How to cite: Chen, X., Barbosa, S., Paatero, J., Kulmala, M., and Junninen, H.: Investigation on the role of elevated gamma radiation in ion production during precipitation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11909, https://doi.org/10.5194/egusphere-egu21-11909, 2021.

Lichen and moss samples were collected from Russian Arctic areas (Kola Peninsula, Franz Josef Land and few other locations) in the 1990s. In 2020, ¹³⁷Cs was determined by HPGe gamma spectrometry from these samples after which isotopes of Pu and U were radiochemically separated from the samples. Mass ratios ²⁴⁰Pu/²³⁹Pu and ²³⁵U/²³⁸U were determined by ICP-MS for utilizing the characteristic isotopic fingerprints of different nuclear events. The aim of the work was to survey radioactive contamination sources in terrestrial environment in Russian Arctic regions, which have not yet been completely explored in respect to anthropogenic isotopes and their origin in the environment.

How to cite: Salminen-Paatero, S., Dutheil, P., Sundström, T., Rodushkin, I., and Paatero, J.: Determination of anthropogenic contamination by 137Cs, 240Pu/239Pu and 235U/238U in lichens and mosses from Russian Arctic areas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12997, https://doi.org/10.5194/egusphere-egu21-12997, 2021.

As a consequence of Council Directive 2013/59/EURATOM and its transposition into national law, the German States (Länder) had to define radon-prone areas where special rules apply in order to assure protection against excessive exposure to Radon-222 in living spaces and at work. The state of Saxony-Anhalt has chosen to define these areas based on datasets of long-term average indoor Rn concentration and Rn concentration in soil-air, complemented by ambient dose rate (ADR), whose values were acquired by a measurement campaign throughout the state territory.

Saxony-Anhalt is characterized by sabulous lowlands in its northern part with little Rn exhalation, but also by granite in the secondary mountains of the Harz massif and copper-shale dominated areas in the south. Radon prone areas can therefore be expected in the latter regions.

ADR was measured from vehicles carrying both a bGeigie nano pancake detector (the standard device of the Safecast mapping project, https://safecast.org/) with automatic GPS geo-referencing and a Thermo Eberline ESM FHZ 672-2 plastic scintillator. The latter device features a natural-background rejection system which could be used to determine high ADR levels as a consequence of K-40 anomalies that needed to be rejected. An ADR map could be created which was statistically linked to geogenic Rn data and soil geochemistry.

The purpose of the resulting model is to develop an algorithm that makes ADR a predictor for identifying radon-prone areas, which is sufficiently accurate for the objective of Rn legislation. It can be used in regions lacking of indoor Rn concentration or soil-sample data, on which the identification of such areas is usually based, but whose acquisition is too time and labour consuming to be achievable in the time frame allowed for implementation of Rn legislation.

It could be demonstrated that the gamma-dose rate can be used as an additional predictor for the identification of radon-prone areas with an algorithm that applies selective averaging on the data obtained on 2 500 km of measuring trips throughout the entire state of Saxony-Anhalt.

In this contribution, the algorithm is presented together with the areas the State of Saxony-Anhalt has finally determined as radon prone, with the legal consequence for employers to do quality assured Radon measurements and take action with respect to radon mitigation, if necessary. Special emphasis is put on establishing a statistically significant relationship between the measured dose rate on the one hand and geological information and radon exhalation, on the other.

How to cite: Ilgner, C., Bossew, P., and Schneider, P.: Ambient dose rate as an additional predictor for the identification of radon-prone areas as used in the German State of Saxony-Anhalt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15633, https://doi.org/10.5194/egusphere-egu21-15633, 2021.

Polonium-210 (Po-210) is a naturally occurring high-energy alpha emitter with a high dose coefficient compared to other natural radionuclides. In groundwater, Po-210 concentrations usually are low due to its high surface reactivity and tendency to readily adsorb onto mineral surfaces. The nationwide median in drinking water in Germany is 1.4 mBq/L as shown by investigations of the Federal Office for Radiation Protection (BfS). However, some sites in southern Sachsen-Anhalt in Germany were revealed to have Po‑210 activity concentrations far above 100 mBq/L. This is of particular relevance, since the EU Council Directive 2013/51/Euratom and its national implementation in the German Drinking Water Ordinance specifies requirements for drinking water quality with regard to artificial and natural radioactive substances. These high values of Po-210 would require reduction measures according to legislation.  

In order to gain a better understanding of the occurrence and origin of Po-210 in groundwater, further groundwater wells and water supply facilities in southern Sachsen-Anhalt were selected for analysis, taking into account the regional geology. The investigated aquifers pertain to the rock sequences of the Lower, Middle and Upper Buntsandstein (Lower Triassic), the Lower Muschelkalk (Middle Triassic) and Cenozoic stratigraphic units. Unfiltered water samples from 50 sites in total were analyzed for their content of natural radionuclides, major and trace elements as well as their oxygen and hydrogen isotope composition and supplemented by the examination of drill core material from these rock sequences.

The data indicate that the elevated Po-210 activity concentrations are limited to the aquifer of the Middle Buntsandstein. The simultaneous absence of the parent nuclides lead-210 (Pb-210) and radon-222 in the water samples indicate a local release mechanism in the rock. In the Middle Buntsandstein the amount of Pb-210 would be sufficient to provide the amount of Po-210 found in solution and the available clay minerals like illite, chlorite, hematite and muscovite could serve as potential hosts for Pb-210 and Po-210. Redox-indicators and a relatively high content of dissolved organic material (DOC >1 mg/L) found in the water samples of the Middle Buntsandstein aquifer could be interpreted as an indication of microbially induced reduction processes.

Understanding the geochemical processes responsible for the mobilization of Po-210 could provide necessary information helping to minimize the human exposure caused by drinking water consumption. Therefore, further investigations will focus on the size distribution of Po-210-bearing particles, the presence of the short-lived mother nuclide bismuth-210 and the sulfate isotope distribution at selected Po-210-rich groundwater sites in this study area.

How to cite: Hofmann, P., Wagner, F., Lucks, C., and Wittwer, C.: Occurrence and origin of polonium-210 in a sandstone aquifer in Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-69, https://doi.org/10.5194/egusphere-egu21-69, 2021.

The August, 2 2017 Decree, which standardized the health protection requirements from the presence of radioactive substances in the waters intended for human consumption, provides for the obligation to verify the value of two parameters relating to the radioactivity content in drinking water: the concentration of tritium, which must be less than 850 UT (unit of tritium), and the total indicative dose, related to ingestion, which must be less than 0.1 mSv / year.

Tritium atoms produced in the atmosphere, by combination with oxygen in the air, tritiated water (HTO) which, having greater molecular mass than the H2O molecule, has a shorter residence time in the atmosphere from which it tends to be removed with precipitation. The short periods of residence in the atmosphere and the short period of decay mean that the concentrations of tritium in the rains are low and almost constant, as there is a balance between the speed of formation, the removal by the rains and the total quantity of natural tritium in the environment which is ∼ 70 × 106 Ci (US Department of Energy, 2002). This means that in groundwater with a long residence time in subsoil, infiltrated before 1950 (nuclear test period), the concentration of tritium is below the analytical detection limit.

In 1960, rainwater had an abnormal concentration (due to the emission into the atmosphere following nuclear tests) corresponding to an average value of 1000 UT. In the subsoil the decay of tritium produces its continuous loss which, in the absence of rainwater recharge and without the compensation of new atmospheric inputs, causes a decrease. To date, in the absence of any infiltration, this water would contain 35 UT.

Given that waters with over 50 years generally have dilution factors from 10 to 20 times with tritium-free fossil water, today we expect, due to mixing, detectable UT values but lower than 4. Aquifer values greater than 9 UT would therefore be related to recent anthropogenic recharge or surface percolation factors.

In the case of recharge with rain water rich in tritium, the concentration reflects the balance between the loss due to decay and the supply of rain water enriched with tritium. Based on the abundance of tritium, in the absence of sources of anthropogenic contamination it is possible to establish the average age of groundwater under the age of 50. This data is very important, because by analyzing the concentrations of tritium present in groundwater it is possible to trace the age of the aquifer and / or define if the aquifer is polluted by anthropogenic activities.

ENEA's Environmental Traceability and Radiometry Laboratory is at the forefront of the analysis of radioisotopes in the environment, including low-concentration of tritium analyzes. In this regard, an activity with ARPAV of Treviso was started for the determination and evaluation of the concentrations of tritium found in groundwater samples of the area around the city of Treviso.

How to cite: Telloli, C., Rizzo, A., Salvi, S., and Ubaldini, A.: Characterization and analysis of groundwater recharge through tritium measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-490, https://doi.org/10.5194/egusphere-egu21-490, 2021.

Radon-222, ²²²Rn, is a naturally radioactive noble gas with a half-life of 3.82 days. It is a product of the ²³⁸U disintegration chain with ²²⁶Ra as parent isotope. Radon gas has traditionally been linked to magmatic and seismic activity.

In order to improve volcanic surveillance networks, ²²²Rn monitoring in volcanic areas is carried out by measuring its concentration in air and soils. Also, since radon-222 is soluble in water, the gas may also be dissolved into groundwater flows. The quantity of dissolved ²²²Rn depends on different factors such as the characteristics of the aquifer, water-rock interaction, water residence time and material content of radium.

In Tenerife there are a vast number of excavated galleries, subhorizontal water mining tunnels, that drain the main aquifer in the island. Thirteen of them have been selected in order to monitor the dissolved radon-222 concentration since October 2019 every three months. This set of galleries surrounds the main volcanic complex in the island, Teide-Pico Viejo, located in Las Cañadas caldera in central Tenerife. 

Before sampling, 10 ml of Opti-Fluor O scintillation cocktail for selective extraction of radon-222, two-phase counting method, was transferred into a 20 ml vial. During the sampling, 10 ml of water were injected into the bottom of the vial. The vial was then tightly capped, vigorously shaken and transported to the laboratory for analysis. Water samples were measured using the liquid scintillation system Quantulus 1220 from PerkinElmer.

In this work, we show the main and preliminary results, which includes both spatial and temporal distribution of the dissolved radon concentration measured in the selected sampling points for the studied period. There are galleries showing a high stability, with radon-222 activity concentrations around 20 Bq/L, whereas others show a clear seasonal influence. The maximum dissolved ²²²Rn value detected was 29.2 ± 2.1 Bq/L. The detection limit is 0.5 Bq/l using a 30 minutes counting time. Besides, this dataset has been compared to data previously reported by other authors, in order to find changes in dissolved radon-222 emission across time. Finally, in the aim of finding interesting relationships, dissolved ²²²Rn values have been studied together with in situ groundwater parameters measured in the field (temperature, pH and electric conductivity) and, in some of the sampling points, also with dissolved CO₂ concentration and isotopic ratio ³He/⁴He corrected for air contamination, (R/R_a)_c, which are parameters directly related to volcanic activity.

How to cite: Torres González, P. A., Luengo Oroz, N., and Pujol, L.: Monitoring dissolved radon-222 in groundwater in a volcanic island (Tenerife, Canary Islands), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5233, https://doi.org/10.5194/egusphere-egu21-5233, 2021.

Groundwater represents a vast majority of the readily accessible fresh water on Earth and satisfies the demand for drinking water for a large portion of the world population. However, groundwater quality can be seriously threatened by geogenic and anthropogenic contamination with elevated concentrations of hydrocarbons, pesticides, metal(loid)s or radionuclides. Understanding the controls of the release and mobility of these contaminants including radionuclides is critical in proper groundwater management. In the southern foreland of a granitic outcrop in Hungary, gross alpha activity exceeding the 0.1 Bq L^–1 limit was measured in drinking water wells. Nuclide-specific measurements for uranium, radium and radon isotopes were involved. The sampling activities indicate that excess of uranium (3−753 mBq L⁻¹) is mainly responsible for the natural radioactivity measured in drinking water. Radium was measured in low activity concentrations (<5–63 mBq L⁻¹) with the exception of three specific wells (285–695 mBq L⁻¹). Notable radon activity was measured in the spring waters from Velence Hills (101–314 Bq L⁻¹ ) and in interrelation with the high radium activities. These observations were interpreted in a “groundwater flow system” context. A conceptual model explaining the elevated radioactivity of groundwater was delineated. A geochemical modeling analysis involving redox-controlled kinetic reactions and a surface complexation model was developed to support the conceptual model of uranium mobility. The results suggest that uranium distribution is sensitive to redox changes in the aquifer. Its mobility in groundwater depends on the residence time of water compared to the reaction times controlling the consumption of oxidizing species. The longer the flow route from the recharge point to an observation point where U is measured, the higher the likelihood of finding aquifer reducing conditions and low U concentrations. It is concluded that the joint application of nuclide-specific measurements, hydrogeological approach and geochemical modeling can support safe drinking water management when dealing with the excess of radionuclides in groundwater.

This topic is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980. This study was also supported by the ÚNKP-17-4-III-ELTE-73 New National Excellence Program of the Ministry of Human Capacities (Hungary). The results here presented have been developed in the frame of the MIUR Project “Dipartimenti di Eccellenza 2017—Le Geoscienze per la società: risorse e loro evoluzione”.

How to cite: Baják, P., Csondor, K., Pedretti, D., Muniruzzaman, M., Izsák, B., Vargha, M., Horváth, Á., Pándics, T., and Erőss, A.: The controls of radionuclide mobility in a siliciclastic aquifer in Hungary: Hydrogeological investigations and geochemical modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8804, https://doi.org/10.5194/egusphere-egu21-8804, 2021.

How to cite: Poręba, G., Szymak, A., Moska, P., Tudyka, K., and Adamiec, G.: Internal dose rate in quartz grains: Implications for luminescence dating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14208, https://doi.org/10.5194/egusphere-egu21-14208, 2021.

The objective of this work is to simulate the spectral gamma-ray response of NaI(Tl) scintillation detectors for airborne gamma-ray spectrometry (AGRS) using Monte Carlo radiation transport codes. The study is based on a commercial airborne gamma-ray spectrometry detector system with four individual NaI(Tl) scintillation crystals and a total volume of 16.8 l. Monte Carlo source-detector simulations were performed in an event-by-event mode with the commercial multi-purpose transport codes MCNP6.2 and FLUKA. Validation measurements were conducted using ²⁴¹Am, ¹³³Ba, ⁶⁰Co, ¹³⁷Cs and ¹⁵²Eu radiation sources with known activities and source-detector geometries. Energy resolution functions were derived from these measurements combined with additional measurements of natural Uranium, Thorium and Potassium sources. The simulation results are in good agreement with the experimental data with a maximum relative error in the full-energy peak counts of 10%. In addition, no significant difference between the two Monte Carlo radiation transport codes was found with respect to a 95% confidence level. The validated detector model presented herein can be adopted for angular detector response analysis and calibration computations relating radionuclide activity concentrations with spectral detector counts.

How to cite: Breitenmoser, D.: Experimental and Simulated Spectral Gamma-Ray Response of a NaI(Tl) Scintillation Detector used in Airborne Gamma-Ray Spectrometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1345, https://doi.org/10.5194/egusphere-egu21-1345, 2021.

Glaciers are temporary repositories for radionuclides and other airborne contaminants (eg. heavy metals). Retreat of glaciers results in the release of these contaminants to downstream ecosystems where they can be accumulated by biota, with further consequences along the trophic chain. Fallout radionuclides, and especially Pu released from nuclear weapons testing and nuclear accidents, concentrates on glacier surfaces in cryoconite granules. These aggregates of mineral and organic components are associated with biological consortia composed of archaea, algae, cyanobacteria, fungi and heterotrophic bacteria (Cook et al., 2016). Cryoconite is also responsible for local decrease ice albedo and is responsible for formation of water-filled holes. Contaminants are effectively trapped in cryoconite granules for long periods (up to decades) due to the “sticky” nature of the material. Cryoconite can thus be useful in monitoring of radionuclide deposition on glaciers (Łokas et al., 2019; Giovanni et al., 2020).

Our collective research reveals widespread incidence of Pu isotopes in cryoconite across multiple sites on both hemispheres, including Svalbard, Sweden, Norway, Iceland, Greenland, British Columbia, Alaska, the European Alps, the Caucasus, Siberia, Tien Shan, Altai, South America and Antarctica. The levels of plutonium isotopes (238,239,240Pu) found in cryoconite at these sites are orders of magnitude higher than those detected in non-glaciated environments, raising important questions around the role of glaciers, and specifically cryoconite, in concentrating levels of Pu isotopes above those found in the surrounding environment. The activity ratios of 238Pu/239+240Pu show that the plutonium-related radioactivity of cryoconite from the Northern hemisphere is compatible with the worldwide signal from the global radioactive fallout (0.025) but in some samples from Svalbard higher activity ratios are associated with an additional source of pure 238Pu, pointing to an influence of the SNAP-9A satellite burn up in the atmosphere occurred in 1964. Also activity ratios from South America and Antarctica are consistent with the global radioactive fallout ratio (including SNAP 9 re-entry) in the southern hemisphere (0.14), with an exception concerning cryoconite from the Exploradores Glacier (Chilean Patagonia, ratio 0.35). There are no known nuclear test sites near this glacier which could explain this anomalous value. However, there is also no information about the atmospheric re-entry of the automatic Interplanetary Station “Mars’96” which was launched on 16 November 1996. It fell off the coast of Chile near the border with Bolivia and was not found so far. There were considerable quantities of 238Pu on board of the station, with a total activity of 174 TBq (IAEA, 2001). We hypothesize that this event could explain the anomaly observed at Exploradores Glacier, confirming the unmatched potential of cryoconite to study environmental radioactivity in glacial contexts.

Acknowledgements

This study was supported by the National Science Center grant no. NCN 2018/31/B/ST10/03057.

References

Cook et al., 2016. Progress in Physical Geography, 40(1), 66-111.

Giovanni et al., 2020. CATENA, 191, 104577.

IAEA, 2001. International Atomic Energy Agency IAEA, Vienna).

Łokas et al., 2019. The Cryosphere, 13(7), 2075-2086.

How to cite: Łokas, E., Baccolo, G. B., Clason, C., Wachniew, P., Takeuchi, N., Zawierucha, K., Beard, D., Ambrosini, R., Pittino, F., Franzetti, A., Owens, P., Poniecka, E., Blake, W., Nastasi, M., and Buda, J.: Deposition  of plutonium isotopes in glacial environments in the Northern and Southern Hemispheres, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8795, https://doi.org/10.5194/egusphere-egu21-8795, 2021.