Evaluation of the 210Po method at the Midwest uranium deposit,Northern Saskatchewan,Canada

Vertical profiles of ²¹⁰Po in soils near the Midwest uranium deposit and an associated surficial radioactive sandstone boulder train in northern Saskatchewan show a high ²¹⁰Po background in air-dried forest litter (24 pCi/g) and Ah horizon soil (11 pCi/g) relative to lower soil horizons (<1 pCi/g). These high levels mask the ²¹⁰Po signal from the radioactive boulders in the near-surface soil horizons. Only in the Bf and C horizons can the existence of the radioactive boulders be inferred from ²¹⁰Po determinations. For comparative purposes profiles for ²²⁶Ra, U, Ni, and other trace elements are also presented.Escape of most of the Rn from near surface soils into the atmosphere, homogenization and decay of Rn, and precipitation of decay products back onto surface soils satisfactorily explain the field observations discussed here.Compared to the highly anomalous ²²²Rn signal in soil gases over this boulder train the ²¹⁰Po contrast is very weak and is of little use for prospecting for this type of boulder train. The relatively high ²¹⁰Po background in surficial materials relative to lower soil horizons dictates that great care be taken with the ²¹⁰Po method; the deepest possible horizons should be sampled.     

Uranium, radon, helium and other trace elements and gases in well waters of parts of the St. Lawrence Lowlands, (Ottawa region) Canada

To test the usefulness of groundwater for U prospecting, 130 domestic wells were sampled from a 22,000 km² rectangular area extending south and west from Ottawa, Ontario. The waters were analyzed for twenty variables including ten gases and five trace elements.The dissolved gases give information on subsurface chemical and geological environments. Carbon dioxide highs occur at the contact of granites and limestones; He highs are along major faults; CH₄ and H₂S reveal strongly reducing environments, and O₂ in wells indicates shallow wells or active water turnover. Rn reveals U mineralization and granitic rocks.The South March U-Cu surface occurrence gives coincident U, Cu, Zn, Pb and Rn highs. A weak U-Rn-Cu high in the Richmond-North Gower area suggests more radioactive subcropping March formation there.A strong regional He anomaly coincident with the outcropping Rockcliffe Formation and controlled by the Hazeldean Fault is believed to be due to deep-seated He, but its coincidence with a weak regional Cu anomaly, a Rn anomaly in the Bells Corners area, its linear northeast trend, the presence of Helikian U-rich source rocks to the southwest, and northeast-dipping Paleozoic sandstones provide both indications of, and the right environment for epigenetic type U-Cu occurrences.     

The relationship of soil 210Po and 210Pb geochemical dispersion patterns to uranium mineralization

²¹⁰Po and ²¹⁰Pb measurements of soils delineated uranium anomalies at three out of four test sites in Ontario, Canada. Measurements were made of ²¹⁰Po in solutions produced by both complete digestion and partial leaching of soil samples. Direct plating of ²¹⁰Po onto metal plates was followed by measuring the alpha activity. Subsequent plating of ²¹⁰Po in-grown from ²¹⁰Pb in solution several months later confirmed the anomalies.The ²¹⁰Po and ²¹⁰Pb anomalies at three of the test sites coincided with ²²⁶Ra and ²²²Rn anomalies. Samples from the fourth uranium occurrence associated with a known ²²²Rn anomaly failed to show either a ²²⁶Ra anomaly on the one hand, or ²¹⁰Po or ²¹⁰Pb anomalies on the other. This suggests that the ²¹⁰Po and ²¹⁰Pb anomalies were probably produced by the decay of ²²⁶Ra contained within secondary dispersion haloes.Although anomalies due to the ²¹⁰Po and ²¹⁰Pb products of ²²²Rn have now been documented, prospecting methods based on their use as direct tracers of the migration paths of ²²²Rn require much further development.     

The relationship of soil Po and Pb geochemical dispersion patterns to uranium mineralization

²¹⁰Po and ²¹⁰Pb measurements of soils delineated uranium anomalies at three out of four test sites in Ontario, Canada. Measurements were made of ²¹⁰Po in solutions produced by both complete digestion and partial leaching of soil samples. Direct plating of ²¹⁰Po onto metal plates was followed by measuring the alpha activity. Subsequent plating of ²¹⁰Po in-grown from ²¹⁰Pb in solution several months later confirmed the anomalies.The ²¹⁰Po and ²¹⁰Pb anomalies at three of the test sites coincided with ²²⁶Ra and ²²²Rn anomalies. Samples from the fourth uranium occurrence associated with a known ²²²Rn anomaly failed to show either a ²²⁶Ra anomaly on the one hand, or ²¹⁰Po or ²¹⁰Pb anomalies on the other. This suggests that the ²¹⁰Po and ²¹⁰Pb anomalies were probably produced by the decay of ²²⁶Ra contained within secondary dispersion haloes.Although anomalies due to the ²¹⁰Po and ²¹⁰Pb products of ²²²Rn have now been documented, prospecting methods based on their use as direct tracers of the migration paths of ²²²Rn require much further development.     

Ra-226 and Rn-222 in saline water compartments of the Aral Sea region

The Aral Sea has been shrinking since 1963 due to extensive irrigation and the corresponding decline in the river water inflow. Understanding of the current hydrological situation demands an improved understanding of the surface water/groundwater dynamics in the region. ²²²Rn and ²²⁶Ra measurements can be used to trace groundwater discharge into surface waters. Data of these radiometric parameters were not previously available for the study region. We determined ²²²Rn activities after liquid phase extraction using Liquid Scintillation Counting (LSC) with peak-length discrimination and analyzed ²²⁶Ra concentrations in different water compartments of the Amu Darya Delta (surface waters, unconfined groundwater, artesian water, and water profiles from the closed Large Aral Sea (western basin).The water samples comprise a salinity range between 1 and 263 g/l. The seasonal dynamics of solid/water interaction under an arid climate regime force the hydrochemical evolution of the unconfined groundwater in the Amu Darya Delta to high-salinity Na(Mg)Cl(SO₄) water types. The dissolved radium concentrations in the waters were mostly very low due to mineral over-saturation, extensive co-precipitation of radium and adsorption of radium on coexisting solid substrates.The analysis of very low ²²⁶Ra concentrations (<10 ppq) at remote study sites is a challenge. We used the water samples to test and improve different analytical methods. In particular, we modified a procedure developed for the α-spectrometric determination of ²²⁶Ra after solid phase extraction of radium using 3M Empore™ High Performance Extraction Disks (Purkl, 2002) for the analysis of the radionuclide using an ICP sector field mass spectrometer. The ²²⁶Ra concentration of 17 unconfined groundwater samples ranged between 0.2 and 5 ppq, and that of 28 artesian waters between <0.2 and 13 ppq. The ICP-MS results conformed satisfactorily to analytical results based on γ-measurements of the ²²²Rn ingrowth after purging and trapping on super-cooled charcoal. The ²²⁶Ra concentrations were positively correlated with the salinity and the dissolved NaCl concentrations. The occurrence of unusually high ²²⁶Ra activities is explained by radium release from adsorption sites with increasing salinity. The inferred spatial variability of ²²²Rn in the Aral Sea and of ²²²Rn and ²²⁶Ra in the groundwater of the Amu Darya Delta is discussed in the context of our own previous hydrochemical studies in the study sites. Relatively low ²²²Rn activities in the unconfined GW (1–9.5 Bq/l) indicate the alluvial sediments hosting the GW to be a low-²³⁸U(²²⁶Ra) substrate. Positive correlations between U and ²²⁶Ra, and U and ²²²Rn are likely related to locally deposited Fe(Mn)OOH precipitates. The ²²²Rn activity of the GW, however, distinctly exceeds the ²²²Rn concentration in the Aral Sea (10 mBq/l), in principle, making ²²²Rn a sensitive tracer for the inflow of GW. The high water volume of the Large Aral Sea and wind induced mixing of its water body, however, hamper the detection of local groundwater inflow.     

The transport of U- and Th-series nuclides in sandy confined aquifers

Abundances of ²³⁸U, ²³⁴U, ²³²Th, ²²⁶Ra, ²²⁸Ra, ²²⁴Ra, and ²²²Rn were measured in groundwaters of the Ojo Alamo aquifer in northwest New Mexico. This is an arid area with annual precipitation of ∼22 cm. The purpose was to investigate the transport of U-Th series nuclides and their daughter products in an old, slow-moving groundwater mass as a means of understanding water-rock interactions and to compare the results with a temperate zone aquifer. It was found that ²³²Th is approximately at saturation and supports the view of Tricca et al. (2001) that Th is precipitated irreversibly upon weathering, leaving surface coatings of ²³²Th and ²³⁰Th on aquifer grains. Uranium in the aquifer waters has very high [²³⁴U/²³⁸U] ∼ 9 and low ²³⁸U concentrations. These levels can be explained by low weathering rates in the aquifer (w_238U ∼ 2 × 10⁻¹⁸ to 2 × 10⁻¹⁷s⁻¹) using a continuous flow, water-rock interaction model. The Ra isotopes are roughly in secular equilibrium despite their very different mean lifetimes. The ²²²Rn and ²²⁸Ra isotopes in the aquifer correspond to ∼10% of the net production rate of the bulk rock. This is interpreted to reflect an earlier formed irreversible surface coating of Th that provides Ra and Rn to the aquifer waters. The surface waters that appear to be feeding the aquifer have low [²³⁴U/²³⁸U] and high ²³⁸U concentrations. The flow model shows that it is not possible to obtain the high [²³⁴U/²³⁸U] and low [²³⁸U] values in the aquifer from a source like the present vadose zone input. It follows that the old aquifer waters studied cannot be fed by the present vadose zone input unless they are greatly diluted with waters with very low U concentrations. If the present sampling of vadose zone sources is representative of the present input, then this requires that there was a major change in water input with much larger rainfall some several thousand years ago. This may represent a climatic change in the Southwest.     

Radon-222 in medicinal groundwaters of Szczawno Zdrój (Sudety Mountains, SW Poland)

 Radon is a significant component of the groundwaters that discharge in the springs of Szczawno Zdrój and are recognized as medicinal. However, among the five exploited springs adjoining each other, it is only in Marta Spring that radon occurs in large concentrations (up to 325.6 Bq/dm³). Therefore, the authors have made an attempt to describe and clarify this fact. They found out from their own research and archival data that ²²²Rn dissolves in the waters of Marta Spring after acidulous waters of deep circulation have mixed with poorly mineralized shallow waters in their outflow zone. The genesis of the gas is determined by the content of its parent nuclide, ²²⁶Ra, in the sandstones in the vicinity of the intake. The volume of the rocks providing radon to the waters of this intake has been estimated at several hundred cubic metres. No seasonal fluctuations in radon concentration have been observed and ²²²Rn concentration changes do not seem to be influenced by changes in the concentration of other chemical components of the waters or by the discharge of the intake. The process of dissolving ²²²Rn in the medicinal groundwaters of Marta Spring is the last, the shortest, and the most local of the processes that form the chemical composition and the physical properties of these waters. Received: 7 January 2000 · Accepted: 12 August 2000     

On 226Ra and 222Rn concentrations in the brackish waters of coastal aquifers: lab-investigations and confirmation in the carbonate aquifer of Brindisi (Italy)

The ground waters circulating in the Apulian mesozoic carbonate aquifer, of coastal type, show high concentrations of ²²²Rn everywhere. Considering their variation during the different phases of a hydrological year, such high concentration values can reach activity of 20 Bq/L, in the more internal zones of the aquifer. Moreover, it is often observed that, in correspondence of wells and springs nearest the coast, the concentrations of radioactive gas reach values greater than 400 Bq/L and vary considerably during the course of a day and with withdrawals. The research carried out over the last few years, has confirmed that ²²⁶Ra and ²²²Rn concentrations in the karst groundwater of Apulia, are mainly related to the occurrence of Terra Rossa inside the aquifer and the capacity of these paleosols to fix the salts of ²²⁶Ra coming from the dissolution of the calcareous and calcareous-dolomitic rocks. This paper shows the results of the analysis performed to define ²²²Rn increase in the brackish waters that come in contact with carbonate rocks and terra rossa. It also indicates the results of surveys performed in a coastal zone with well-known hydrogeological features. The controls performed during one hydrological year, have confirmed the relationships between the salt content of the ground waters and the enrichment of ²²²Rn and have highlighted that the manner of increase of this radioisotope is related to cases of ionic exchange and adsorption regulated by the dynamics of marine intrusion.     

Effect of groundwater on the ecological water environment of typical inland lakes in the Inner Mongolian Plateau

To explore the causes of the ecological environment deterioration of lakes in the Inner Mongolia Plateau, this study took a typical inland lake Daihai as an example, and investigated the groundwater recharge in the process of lake shrinkage and eutrophication. Using the radon isotope (²²²Rn) as the main means of investigation, the ²²²Rn mass balance equation was established to evaluate the groundwater recharge in Daihai. The spatial variability of ²²²Rn activity in lake water and groundwater, the contribution of groundwater recharge to lake water balance and its effect on nitrogen and phosphorus pollution in lake water were discussed. The analysis showed that, mainly controlled by the fault structure, the activity of ²²²Rn in groundwater north and south of Daihai is higher than that in the east and west, and the difference in lithology and hydraulic gradient may also be the influencing factors of this phenomenon. The ²²²Rn activity of the middle and southeast of the underlying lake is greater, indicating that the ²²²Rn flux of groundwater inflow is higher, and the runoff intensity is greater, which is the main groundwater recharge area for the lake. The estimated groundwater recharge in 2021 was 3 017×10⁴ m³, which was 57% of the total recharge to the lake, or 1.6 times and 8.1 times that of precipitation and surface runoff. The TN and TP contents in Daihai have been rising continuously, and the average TN and TP concentrations in the lake water in 2021 were 4.21 mg·L^?1 and 0.12 mg·L^?1, respectively. The TN and TP contents entering the lake with groundwater recharge were 6.8 times and 8.7 times above those of runoff, accounting for 87% and 90% of the total input, respectively. The calculation results showed that groundwater is not only the main source of recharge for Daihai, but also the main source of exogenous nutrients. In recent years, the pressurized exploitation of groundwater in the basin is beneficial in increasing the groundwater recharge to the lake, reducing the water balance difference of the lake, and slowing down the shrinking degree of the lake surface. However, under the action of high evaporation, nitrogen and phosphorus brought by groundwater recharge would become more concentrated in the lake, leading to a continuous increase in the content of nutrients and degree of eutrophication. Therefore, the impact of changes in regional groundwater quantity and quality on Daihai is an important issue that needs further assessment.     

Pedogeochemical models on prognosis and control of radon fluxes from humid tropical landscapes over granite

The principal relationships between radon (²²²Rn and ²²⁰Rn) exhalation intensities and the morpho-dynamic elements of humid tropical landscapes have been established and analyzed with the objective of elaborating Rn exhalation models, which can be used on the scale of small habitational nuclei. The current radioactive processes of generation, emanation and migration of Rn, in relation to its exhalation rates on a landscape slope of granitic rock having normal U and Th contents, were correlated with the latosol-podzolic soil association developed as a product of supergene processes during geological and pedological times and also with the water regime of an overlying phreatic aquifer. This approach, encompassing pedogeochemical models of radionuclide dispersion linked to soil systems and surface geochemistry, was framed within a tridimensional, interdisciplinary and systemic focus, using concepts of nuclear physics, climate and hydrogeology. The characteristic signatures of elementary landscapes include (1) different landforms, namely eluvial, transeluvial and superaqual, (2) residual soils having varying types, thicknesses and perma-porosities and (3) radioanomalies corresponding to different U and Th concentrations, secondary hosting minerals and also to different pedological ages. Considering these factors and their spatial relationships and on the basis of moisture content of soils, it is postulated that the highest Rn exhalation rates, especially of ²²²Rn, are confined to superaqual and transeluvial landscapes. In an eluvial landscape, the Rn fluxes are found to be less important even though gamma anomalies exist mainly due to the presence of resistant minerals containing U and Th. In short, the products of supergene alteration organized in a sloping system can exhibit Rn exhaling intensities higher than that measured on unaltered subjacent rock. Hence, the understanding of U, Th, Ra and Rn behavior on a surface environment is fundamental for the formulation of prognostic Rn exhalation models associated with the elementary humid tropical landscapes. Further, the pedogeochemical information provides important clues supplementing the lithostructural data for delineating preferential sites of Rn fluxes especially on scales compatible to small habitational nuclei or unitary dwellings.     

Statistical analysis of the radon-222 potential of rocks in Virginia,U.S.A.

More than 3,200 indoor radon-222 (²²²Rn) measurements were made seasonally in an area of about 1,000 square kilometers of the Coastal Plain and Piedmont physiographic provinces in Virginia, U.S.A. Results of these measurements indicate that some geological units are associated, on the average, with twice as much indoor²²²Rn as other geological units, and that indoor²²²Rn varies seasonally. The Kruskal-Wallis test was used to test whether indoor²²²Rn concentrations for data gathered over the winter and summer seasons differ significantly by rock unit. The tests concluded that indoor²²²Rn concentrations for different rock units were not equal at the 5-percent significance level. The rocks associated with the highest median indoor²²²Rn concentration are specific rocks in the Mesozoic Culpeper basin, including shale and siltstone units with Jurassic diabase intrusives, and mica schists in the Piedmont physiographic province. The pre-Triassic Peters Creek Schist has the highest ranking in terms of indoor²²²Rn concentration. The rocks associated with the lowest indoor²²²Rn concentrations include coastal plain sediments, the Occoquan Granite, Falls Church Tonalite, Piney Branch Mafic and Ultramafic complex, and unnamed mafic and ultramafic inclusions, respectively. The rocks have been ranked according to observed²²²Rn concentration by transforming the average rank of indoor²²²Rn concentrations to z scores.     

Radon concentrations in soil gas,considering radioactive equilibrium conditions with application to estimating fault-zone geometry

A calculation method for determining the amount of Rn isotopes and daughter products at the start of measurement (CRAS) is proposed as a more accurate means of estimating the initial Rn concentration in soil gas. The CRAS utilizes the decay law between ²²²Rn and ²²⁰Rn isotopes and the daughter products ²¹⁸Po and ²¹⁶Po, and is applicable to α-scintillation counter measurements. As Rn is both inert and chemically stable, it is useful for fault investigation based on the soil gas geochemistry. However, the total number of α particles emitted by the decay of Rn has generally been considered to be proportional to the initial Rn concentration, without considering the gas condition with respect to radioactive equilibrium. The CRAS method is shown to be effective to derive Rn concentration for soil gases under both nonequilibrium conditions, in which the total number of decays increases with time, and equilibrium conditions, which are typical of normal soil under low gas flux. The CRAS method in conjunction with finite difference method simulation is applied to the analysis of two active fault areas in Japan, and it is demonstrated that this combination could detect the sharp rises in ²²²Rn concentrations associated with faults. The method also allows the determination of fault geometry near the surface based on the asymmetry variation of the Rn concentration distribution when coupled with a numerical simulation of ²²²Rn transport. The results for the new method as applied to the two case studies are consistent with the data collected from the geological survey. It implies that the CRAS method is suitable for investigating the fault system and interstitial gas mobility through fractures. The present analyses have also demonstrated that high Rn concentrations require the recent and repeated accumulation of ²²²Rn parents (²³⁰Th and ²²⁶Ra) in fault gouges through deep gas release during fault movement.     

Multi-tracer investigation of river and groundwater interactions: a case study in Nalenggele River basin,northwest China

Environmental tracers (such as major ions, stable and radiogenic isotopes, and heat) monitored in natural waters provide valuable information for understanding the processes of river–groundwater interactions in arid areas. An integrated framework is presented for interpreting multi-tracer data (major ions, stable isotopes (²H, ¹⁸O), the radioactive isotope ²²²Rn, and heat) for delineating the river–groundwater interactions in Nalenggele River basin, northwest China. Qualitative and quantitative analyses were undertaken to estimate the bidirectional water exchange associated with small-scale interactions between groundwater and surface water. Along the river stretch, groundwater and river water exchange readily. From the high mountain zone to the alluvial fan, groundwater discharge to the river is detected by tracer methods and end-member mixing models, but the river has also been identified as a losing river using discharge measurements, i.e. discharge is bidirectional. On the delta-front of the alluvial fan and in the alluvial plain, in the downstream area, the characteristics of total dissolved solids values, ²²²Rn concentrations and δ¹⁸O values in the surface water, and patterns derived from a heat-tracing method, indicate that groundwater discharges into the river. With the environmental tracers, the processes of river–groundwater interaction have been identified in detail for better understanding of overall hydrogeological processes and of the impacts on water allocation policies.     

Ra and Rn isotopes as natural tracers of submarine groundwater discharge in the patagonian coastal zone (Argentina): an initial assessment

Submarine groundwater discharge (SGD) is herein recognized as a significant pathway of material transport from land to the coastal SW Atlantic Ocean and thus, it can be a relevant factor affecting the marine biogeochemical cycles in the region. This paper focuses on the initial measurements of ²²⁶Ra, ²²⁸Ra and ²²²Rn made in Patagonia’s coastal zone of Chubut and Santa Cruz provinces (42°S–48°S, Argentina). ²²⁶Ra activity ranged from 2.9 to 73.5 dpm 100 L^?1, and ²²⁸Ra activity ranged from 11.9 to 311.0 dpm 100 L^?1 in groundwater wells. The radium activities found in Patagonia’s marine coastal regions and adjacent shelf indicate significant enrichment throughout the coastal waters. Groundwater samples presented the largest ²²²Rn activity and ranged from 2.66 to 1083 dpm L^?1. Conversely, in the coastal marine environment, the ²²²Rn activity ranged from 1.03 to 6.23 dpm L^?1. The Patagonian coastal aquifer showed a larger enrichment in ²²⁸Ra than in ²²⁶Ra, which is a typical feature for sites where SGD is dominant, probably playing a significant role in the biogeochemistry of these coastal waters.     

Analysis of the exchange of groundwater and river water by using Radon-222 in the middle Heihe Basin of northwestern China

In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plain. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction of groundwater with surface water to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. As the concentration of Radon-222 (²²²Rn) in groundwater is much higher than in surface water, the use of ²²²Rn was examined as an indicator for the analysis of the interaction between surface water and groundwater. Measurement of the ²²²Rn concentration in surface water was conducted to detect groundwater seepage into a stream in the middle Heihe Basin of northwestern China. Furthermore, the simultaneous groundwater flow into and out of a stream from the aquifers was quantified by solving the ²²²Rn mass balance equation, in which the losses of gas exchange and radioactive decay of ²²²Rn are considered. Meanwhile, river runoff was gauged to determine the exchange rates between surface water and groundwater. The result shows that ²²²Rn isotope can be used as a good environmental tracer with high sensitivity for the interaction between surface water and groundwater, especially in the fractured aquifer system, karst aquifer system and discharge basins.     

A comparison of measured 137Cs and excess 210Pb levels in the cultivated brown and cinnamon soils of the Yimeng Mountain area

This contribution analyzes the similarities and differences between the measured activities of 137Cs and excess 210pb （210Pbex） in the cultivated brown and cinnamon soils of the Yimeng Mountain area, discusses the influ- ence of soil texture on the measurement of 210Pbex, and presents differences between the two types of soils. Fields A and B were selected to represent the fields that contain cultivated brown and cinnamon soils, respectively. From either study field, one site of sectioned core and six bulk cores were collected to measure 137Cs levels, 210Pbex levels, and the particle-size composition of soil samples. Three undisturbed soil samples were collected to measure capillary and aeration porosities. The 137Cs inventories for the two study fields are very similar. The 137Cs is a man-made ra- dionuclide, which means that its measured levels for soils are unaffected by soil texture. In contrast, levels of the naturally occurring 210Pbex of soils from Field A were lower than those of Field B by about 50%. In contrast to aquatic sediments, levels of 210Pbex in terrestrial surface soils are affected by the emanation of 222Rn from the soils. It can be assumed that the coarser the soils, the greater the emanation of 222Rn; in addition, the lower the measured 210pbex, the greater the underestimate of this value. The cultivated brown soils in Field A are coarser than the culti- vated cinnamon soils in Field B. As a result, 222Rn in Field A will diffuse more easily into the atmosphere than that in Field B. As a consequence, the measured 210pbex in soils from Field A is much lower than the actual value, whereas the value measured for Field B is much closer to the actual value.     

Seasonal variations of helium,radon, and uranium in lake waters near the Key Lake uranium deposit,Saskatchewan

To test the usefulness of the He method for the detection of buried U ore, a lake-water survey of the Key Lake area was carried out during March 1977 and repeated in June 1977. A set of 87 lake-water samples from 37 sites in eight different lakes were collected from the same sites in each survey. These samples were analyzed for He, Rn, O₂, Eh, pH, conductivity, alkalinity, and U.In the lakes the highest He concentrations, of nearly four times atmospheric equilibrium concentrations, were obtained during the winter survey. This was under the ice in two bottom lake samples where the sandy overburden extends for some 50 m directly to the ore zone. Radon and U values at these sites were also anomalous, but the highest values of Rn and U were obtained in a shallow lake about 2 km south of the ore zone where concentrations of radioactive boulders occur.The average net He and Rn contents dropped from 21 standard nanolitres/litre (nl/l) and 25 picocuries/litre (pCi/l) in the winter under the ice to 3 nl/l and 8 pCi/l in the summer, respectively. Average U and conductivity dropped from 2.3 ppb and 15 μmho/cm to 1.5 ppb and 11 μmho/cm, respectively, in the same suites of samples. The drop in the ionic species probably reflects the effect of snow and ice meltwater dilution and the much larger drop in the dissolved He and Rn reflects the combined effects of meltwater dilution, wind turbulence over ice-free lakes, and change in thermal gradients.The He results must be viewed with guarded optimism until a detailed investigation is completed to ascertain what fraction of the detected He is from the ore, what fraction from basement He that may have found its way into the lakes via the fracture zone in which the ore is located, and what effect drilling has had on the He flow into the lakes from the ore zone.     

Use of radon isotopes,gamma radiation and dye tracers to study water interactions in a small stream in Brazil

In this study, natural (²²²Rn) and fluorescent (uranin) tracers were used to investigate the interactions between surface and subsurface waters in a small hydrographical basin located in the southeast region of Brazil. Levels of ²²²Rn were measured in 117 water samples with the use of an alpha solid-state detector. After the identification of the probable discharge sections along the stream, a measurement of the natural flows, upstream and downstream of these sections, was done with the use of a fluorimeter and fluorescent tracers. Also, scanning was done to verify a correlation between the natural gamma radiation and the ²²²Rn in the areas where its activity was higher. The results showed some sections where the ²²²Rn activity is more significant and contributed to the growth of the flows along the stream. It was possible to confirm a correlation between the discharge sections and the natural gamma radiation, what can be used as a preliminary approach to finding these sections in scenarios similar to the one studied here.     

Biogeochemical cycling in an organic-rich coastal marine basin—3. Dissolved gas transport in methane-saturated sediments

The transport of dissolved gases in the anoxic sediments of Cape Lookout Bight, North Carolina, is controlled by diffusion and bubble ebullition and exhibits a distinct seasonal cycle. Detailed seasonal profiles of CH₄, N₂ and ²²²Rn and direct gas flux measurements indicate that ebullition dominates the flux of all dissolved gases across the sediment-water interface during summer months, and is of major importance on an annual basis. Transport within the upper 6–8 cm of sediment appears to be controlled by molecular diffusion of gases. Transport at greater depths is controlled by diffusion in winter and ebullition in summer. Rn-222 profiles were used to estimate the rate of stripping of dissolved gases within the CH₄ production zone (10–30 cm); rates averaged 3–5 percent per day and agreed with estimates derived from N₂ profiles. As a result of summer ebullition, the sediments of the bight are never at saturation with respect to the major gases present in seawater. Evidence from other sites suggests that ebullition may be an important transport process in many coastal sediments, and may provide mechanism for the transport of volatile reduced compounds between anoxic sediments and the atmosphere. ²²²Rn is a useful tracer for quantifying this transport.