Phase II testing of Xenon International on Mount Schauinsland, Germany.

Station RN33 on Mount Schauinsland near Freiburg, Germany, is part of the International Monitoring System monitoring radioxenon in air (131mXe, 133Xe, 133mXe, and 135Xe) for verification of the Comprehensive Nuclear Test Ban Treaty. Here, we present data from phase II testing of a new system, Xenon International at RN33, July 14th, 2021 to Jan 22nd, 2022, together with SPALAX data from the same time period. Radioxenon could be detected in 473 of 719 samples, among them many multiple isotope detections. Activity concentrations of spiked and selected environmental samples were verified by laboratory reanalysis. The sensitivity of Xenon International for radioxenons is up to one order of magnitude better for the metastable isotopes than that of the SPALAX, with a shorter sampling duration of 6 h.

In Memoriam Dr. Clemens Schlosser *April 11, 1961 -†August 2, 2021.

Dr. rer.nat. Clemens Schlosser, a physicist by training, well known to the German and international scientific community for his contributions to the monitoring of environmental radioactivity and especially the radionuclide component of the International Monitoring System, passed away on August 2, 2021 after a long and brave battle with ALS. Even during the last years, during which his illness compromised his strength, he devoted all the time possible to his life's work that was so close to his heart.

Krypton-85 datasets of the northern and southern hemisphere collected over the past 60 years.

With a half-life of 10.7 years, the noble gas radioisotope 85Kr is perfectly suited as a tracer to date ice and water that formed during the past half century. Furthermore, due to its inhomogeneous input into the atmosphere, it is a useful tool to investigate atmospheric circulation and back-trajectory analysis. The data presented here represent a comprehensive time series of atmospheric 85Kr activity concentrations in ground level air that can be used to model northern and southern hemispheric input functions, which is essential to apply 85Kr as a dating tracer. The collection comprises 11 datasets from 4 monitoring stations in the northern and 7 monitoring stations in the southern hemisphere, respectively. In total, it contains about 8000 measurements performed over the past 60 years, making it the largest published 85Kr record.

Radon-222 diffusion length and exhalation characteristics of uraniferous waste rock and application to mine site remediation in the Australian wet-dry tropics.

The diffusion length of 222Rn in uraniferous waste rock was determined through a novel experiment. Large PVC columns were filled to different depths in the range from 0.5 m to 3.0 m with waste rock material from the Ranger uranium mine and the build-up of 222Rn activity concentration in the column headspace above the material was measured after closing the columns with a lid. Measurements were made approximately one month after filling the columns and again after approximately one and two years. The average 222Rn diffusion length derived from the measurements was 1.9 ± 0.2 m in the dry material. The corresponding diffusion coefficient was (7.3 ± 0.7) × 10-6 m2 s-1. For an infinitely thick layer of the dry material, the average value of the 222Rn exhalation flux density relative to the 226Ra activity concentration was estimated as (5.3 ± 0.3) × 10-4 Bq m-2 s-1 per Bq kg-1. From the diffusion length, the waste rock material was characterised as both a source and attenuator of 222Rn for its proposed use as the surface cover on the final landform of the remediated Ranger uranium mine.

Half a century of Krypton-85 activity concentration measured in air over Central Europe: Trends and relevance for dating young groundwater.

For almost half a century weekly samples for the measurement of krypton-85 (85Kr) activity concentrations in surface air have been collected by the Bundesamt für Strahlenschutz (BfS), Germany. Sampling started at Freiburg (230m asl) in 1973, Mt Schauinsland (1205m asl) in 1976 and Mt Jungfraujoch in Switzerland (3454 asl) in 1990. Distinct maxima in the time series of atmospheric 85Kr activity concentration are caused by emissions from nuclear reprocessing plants in Europe, mainly the La Hague, France, and Sellafield, UK, reprocessing plants. Between 1970 and 1990 peak activity concentrations measured in winter along the Rhine Rift in Freiburg are often higher than at Mt Schauinsland, due to emissions from the operating pilot reprocessing plant in Karlsruhe - approximately 130 km to the north - and large-scale inversions that inhibit exchange of air masses within the Rhine Rift with those at higher altitudes. From the early 1990s onwards, after the shut-down of the pilot plant, differences between Freiburg and Schauinsland are much smaller. Activity concentrations measured at Jungfraujoch are generally lower and close to baseline levels, due to its location in the free troposphere. Weekly baseline and average 85Kr activity concentration in the atmosphere in Central Europe were modelled from almost 12,000 individual measurements at 11 stations. The baseline and average have continuously increased, interrupted by a relatively stable period between 2009 and the end of 2014 with a baseline activity concentration of about 1.39 Bq/m3. Depending on the geographical location and hydrological conditions, the modelled baseline or average 85Kr activity concentration time series can be used as input functions for the dating of young groundwater.

Whole-organism concentration ratios in wildlife inhabiting Australian uranium mining environments.

Wildlife concentration ratios for 226Ra, 210Pb, 210Po and isotopes of Th and U from soil, water, and sediments were evaluated for a range of Australian uranium mining environments. Whole-organism concentration ratios (CRwo-media) were developed for 271 radionuclide-organism pairs within the terrestrial and freshwater wildlife groups. Australian wildlife often has distinct physiological attributes, such as the lower metabolic rates of macropod marsupials as compared with placental mammals. In addition, the Australian CRswo-media originate from tropical and semi-arid climates, rather than from the temperate-dominated climates of Europe and North America from which most (>90%) of internationally available CRwo-media values originate. When compared, the Australian and non-Australian CRs are significantly different for some wildlife categories (e.g. grasses, mammals) but not others (e.g. shrubs). Where differences exist, the Australian values were higher, suggesting that site-, or region-specific CRswo-media should be used in detailed Australian assessments. However, in screening studies, use of the international mean values in the Wildlife Transfer Database (WTD) appears to be appropriate, as long as the values used encompass the Australian 95th percentile values. Gaps in the Australian datasets include a lack of marine parameters, and no CR data are available for freshwater phytoplankton, zooplankton, insects, insect larvae or amphibians; for terrestrial environments, there are no data for amphibians, annelids, ferns, fungi or lichens & bryophytes. The new Australian specific parameters will aide in evaluating remediation plans and ongoing operations at mining and waste sites within Australia. They have also substantially bolstered the body of U- and Th-series CRwo-media data for use internationally.

Natural radionuclides and stable elements in weaver ants (Oecophylla smaragdina) from tropical northern Australia.

Natural radionuclides and stable elements were measured in weaver ants, leaves and soils collected from three sites in tropical northern Australia. Radionuclide concentration ratios for ants relative to soil were derived from the measurements and used to refine the current environmental radiological assessment for remediation of Ranger uranium mine. Use of site-specific concentration ratios for weaver ants gave a more conservative estimate of environmental exposure to the arthropod wildlife group than use of default concentration ratios in the ERICA Tool. This was primarily because the 226Ra concentration ratio for weaver ants was more than 7 times greater than for generic arthropods.

Estimating doses from Aboriginal bush foods post-remediation of a uranium mine.

This paper presents a calculator to facilitate assessments of ingestion doses from Aboriginal bush foods. The calculator combines information on traditional diet and land use with radionuclide concentration ratios and ingestion dose coefficients to estimate doses. The calculator was applied to the planned remediation of Ranger uranium mine to derive a set of scaling factors between radionuclide activity concentrations in environmental media and ingestion dose from bush foods. The scaling factors can be used to estimate doses from bush foods once the post-remediation radiological conditions of the mine and surrounding environment are known.

Water hardness determines 226Ra uptake in the tropical freshwater mussel.

Chemical data for freshwater mussels (Velesunio spp.) and water from 15 sampling sites in the Alligator Rivers Region and Rum Jungle uranium provinces in tropical Northern Australia were analysed to develop a predictive model of radium-226 (226Ra) bioaccumulation for variable water calcium (Ca) and magnesium (Mg) concentrations. Application of the model as a 226Ra screening approach for freshwater mussels in tropical waterbodies potentially impacted by operational or remediated uranium mine sites is discussed in relation to Mudginberri Billabong, located approximately 12 km downstream of Ranger uranium mine in the Alligator Rivers Region.

A tool for calculating concentration ratios from large environmental datasets.

This paper presents a tool for calculating concentration ratios from a large and structured environmental dataset of radionuclide activity and metal concentrations. The tool has been developed in MS Excel™ and includes a simple user interface for setting up queries. The tool is capable of matching environmental media samples to biota samples based on user-defined spatial and temporal criteria to derive a representative estimate of the environmental exposure conditions of an organism and its accumulation. Some potential benefits and uses of the tool are discussed.

A database of radionuclide activity and metal concentrations for the Alligator Rivers Region uranium province.

This paper presents a database of radionuclide activity and metal concentrations for the Alligator Rivers Region (ARR) uranium province in the Australian wet-dry tropics. The database contains 5060 sample records and 57,473 concentration values. The data are for animal, plant, soil, sediment and water samples collected by the Environmental Research Institute of the Supervising Scientist (ERISS) as part of its statutory role to undertake research and monitoring into the impacts of uranium mining on the environment of the ARR. Concentration values are provided in the database for 11 radionuclides (227Ac, 40K, 210Pb, 210Po, 226Ra, 228Ra, 228Th, 230Th, 232Th, 234U, 238U) and 26 metals (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Pb, Rb, S, Sb, Se, Sr, Th, U, V, Zn). Potential uses of the database are discussed.

Influence of group II metals on Radium-226 concentration ratios in the native green plum (Buchanania obovata) from the Alligator Rivers Region, Northern Territory, Australia.

In this study, uptake of Ra from soil, and the influence of group II metals on Ra uptake, into the stones and edible flesh of the fruit of the wild green plum, Buchanania obovata, was investigated. Selective extraction of the exchangeable fraction of the soil samples was undertaken but was not shown to more reliably predict Ra uptake than total soil Ra activity concentration. Comparison of the group II metal to Ca ratios (i.e. Sr/Ca, Ba/Ca, Ra/Ca) in the flesh with exchangeable Ca shows that Ca outcompetes group II metals for root uptake and that the uptake pathway discriminated against group II metals relative to ionic radius, with uptake of Ca > Sr > Ba >> Ra. Flesh and stone analysis showed that movement of group II metals to these components of the plant, after root uptake, was strongly related. This supports the hypothesis that Sr, Ba and Ra are being taken up as analogue elements, and follow the same uptake and translocation pathways, with Ca. Comparison with previously reported data from a native passion fruit supports the use of total soil CRs on natural, undisturbed sites. As exchangeable CRs for Ra reach a saturation value it may be possible to make more precise predictions using selective extraction techniques for contaminated or disturbed sites.

Long-term temporal variability of the radon-222 exhalation flux from a landform covered by low uranium grade waste rock.

Radon-222 exhalation flux densities from two different substrates of several metres thickness, waste rock and waste rock mixed with approximately 30% lateritic material, were measured over a period of five years in the wet-dry tropics of Northern Australia. Fourteen measurement campaigns using activated charcoal canisters (n > 1000) covered both dry and wet seasons and showed differences in seasonal and long term trends of the (222)Rn exhalation flux densities normalised to the (226)Ra activity concentrations of the substrate. Dry season (222)Rn exhalation was generally higher for the mixed substrate, due to the larger fraction of fines. Seasonality established within the first year of landform construction on the mixed substrate, due to the higher water holding capacity of the lateritic material. In contrast, waste rock only shows no seasonality until years four and five after construction, when average normalised dry season (222)Rn exhalation flux densities from waste rock increase to values (0.47 ± 0.06 mBq m(-2) s(-1) per Bq kg(-1)) similar to the mixed substrate (0.64 ± 0.08 mBq m(-2) s(-1) per Bq kg(-1)), likely due to an increase in fines from rapid weathering of the schistose waste rock. Volumetric water content has been used to parametrize relative (222)Rn exhalation and we determined that wet season (222)Rn exhalation is about 40% of the dry season exhalation.

A soil radiological quality guideline value for wildlife-based protection in uranium mine rehabilitation.

A soil guideline value for radiological protection of the environment was determined for the impending rehabilitation of Ranger uranium mine in the wet-dry tropics of northern Australia. The guideline value was 1000 Bq kg(-1) of (226)Ra in the proposed waste rock substrate of the rehabilitated landform and corresponded to an above-baseline dose rate of 100 µGy h(-1) to the most highly exposed individuals of the limiting organism. The limiting organism was reptile based on an assessment using site-specific concentration ratio data.

228Ra and 226Ra measurement on a BaSO4 co-precipitation source.

One of the most commonly-used methods for determination of 226Ra, particularly in water samples, utilises co-precipitation of Ra with BaSO4, followed by microfiltration to produce a source for alpha counting. This paper describes two extensions to BaSO4 co-precipitation methods which enable determination of 228Ra using the same source. The adaptations presented here do not introduce any contaminants that will affect the separation of radium or alpha counting for 226Ra, and can be used for re-analysis of already existing sources prepared by BaSO4 co-precipitation. The first adaptation uses detection of 228Ac on the source by gamma spectrometry. The detection efficiency is high, allowing analysis of water samples at sufficiently low activity to be suitable in testing for compliance with drinking water quality standards. As 228Ac grows in quickly, taking less than 2 days to reach equilibrium with the 228Ra parent, this can also be useful in radiological emergency response situations. The second adaptation incorporates a method for the digestion of BaSO4 sources, allowing separation of thorium and subsequent determination of 228Th activity. Although ingrowth periods for 228Th can be lengthy, very low detection limits for 228Ra can be achieved with this technique.

Determining a pre-mining radiological baseline from historic airborne gamma surveys: a case study.

Knowing the baseline level of radioactivity in areas naturally enriched in radionuclides is important in the uranium mining context to assess radiation doses to humans and the environment both during and after mining. This information is particularly useful in rehabilitation planning and developing closure criteria for uranium mines as only radiation doses additional to the natural background are usually considered 'controllable' for radiation protection purposes. In this case study we have tested whether the method of contemporary groundtruthing of a historic airborne gamma survey could be used to determine the pre-mining radiological conditions at the Ranger mine in northern Australia. The airborne gamma survey was flown in 1976 before mining started and groundtruthed using ground gamma dose rate measurements made between 2007 and 2009 at an undisturbed area naturally enriched in uranium (Anomaly 2) located nearby the Ranger mine. Measurements of (226)Ra soil activity concentration and (222)Rn exhalation flux density at Anomaly 2 were made concurrent with the ground gamma dose rate measurements. Algorithms were developed to upscale the ground gamma data to the same spatial resolution as the historic airborne gamma survey data using a geographic information system, allowing comparison of the datasets. Linear correlation models were developed to estimate the pre-mining gamma dose rates, (226)Ra soil activity concentrations, and (222)Rn exhalation flux densities at selected areas in the greater Ranger region. The modelled levels agreed with measurements made at the Ranger Orebodies 1 and 3 before mining started, and at environmental sites in the region. The conclusion is that our approach can be used to determine baseline radiation levels, and provide a benchmark for rehabilitation of uranium mines or industrial sites where historical airborne gamma survey data are available and an undisturbed radiological analogue exists to groundtruth the data.

Radium concentration factors in passionfruit (Passiflora foetida) from the Alligator Rivers Region, Northern Territory, Australia.

In this study, uptake of Ra from soil into the edible fruit of the wild passionfruit species Passiflora foetida was investigated, using selective extraction from the soil samples. A wide range of environmental exposure conditions were represented by the locations that were sampled, including both natural soils, and soils influenced by past and present uranium mining activities. The bioavailable (226)Ra fraction in soils was found to be a better predictor of (226)Ra fruit activity concentrations than the total soil activity concentration, or any of the other fractions studied. Concentration Factors (CFs) derived using the bioavailable fraction varied by only a factor of 7 between different locations, whereas CFs derived using other fractions and total soil varied by up to two orders of magnitude. CFs were highest for those soils containing the lowest concentrations of Mg, Ca and Ba, and approached a saturation value at higher soil concentrations. This finding suggests that group II elements influence radium uptake, most likely the result of increased pressure on the plant to take up essential nutrient group II elements from soil with the lower concentrations, with Ra being taken up as an analogue element. It is also possible that at higher concentrations of bioavailable Ca and Mg in the soil, these ions will outcompete Ra for adsorption sites in the soil and/or on the root surfaces. The study also shows that (228)Ra can potentially be a significant contributor to ingestion doses and should also be considered when assessing committed effective doses from the ingestion of fruits.

A study of radium bioaccumulation in freshwater mussels, Velesunio angasi, in the Magela Creek catchment, Northern Territory, Australia.

Freshwater mussels, Velesunio angasi, along Magela Creek in Australia's Northern Territory were examined to study radionuclide activities in mussel flesh and to investigate whether the Ranger Uranium mine is contributing to the radium loads in mussels downstream of the mine. Radium loads in mussels of the same age were highest in Bowerbird Billabong, located 20 km upstream of the mine site. Variations in the ratio of [Ra]:[Ca] in filtered water at the sampling sites accounted for the variations found in mussel radium loads with natural increases in calcium (Ca) in surface waters in a downstream gradient along the Magela Creek catchment gradually reducing radium uptake in mussels. At Mudginberri Billabong, 12 km downstream of the mine, concentration factors for radium have not significantly changed over the past 25 years since the mine commenced operations and this, coupled with a gradual decrease of the (228)Ra/(226)Ra activity ratios observed along the catchment, indicates that the (226)Ra accumulated in mussels is of natural rather than mine origin. The (228)Th/(228)Ra ratio has been used to model radium uptake and a radium biological half-life in mussels of approximately 13 years has been determined. The long biological half-life and the low Ca concentrations in the water account for the high radium concentration factor of 30,000-60,000 measured in mussels from the Magela Creek catchment.