Rn Emissions Research Articles

Powder sandwich technique: A novel method for determining the thoron emanation potential of powders bearing high 224Ra content

Abstract A new methodology has been developed to measure 220 Rn (thoron) emission from 224 Ra-bearing powders handled in nuclear fuel cycle. In this method, a ‘powder sandwich’ is made by enclosing the powder in between two filter papers in sandwich geometry. This arrangement ensures that the thickness of powder sample is much less than the thoron diffusion length, avoiding any loss of thoron due to matrix absorption and supports complete removal of thoron gas emanated from the powder. The technique utilizes a closed loop setup in which thoron emanated from the powder sandwich is removed using flow through arrangement and is measured using suitable thoron detector. The thoron mass exhalation rate for the powder is estimated using a mass balance model from the measured equilibrium thoron concentration. Subsequently, the thoron emanation coefficient is estimated using the thoron mass exhalation rate and 224 Ra content of the powders. The applicability of the methodology has been demonstrated for three different powders.

Radon surveys and real-time monitoring at Stromboli volcano: Influence of soil temperature, atmospheric pressure and tidal forces on 222Rn degassing

We used a network of stations to perform systematic radon surveys at Stromboli volcano. The time series of periodic measurements show that monthly average 222Rn emissions reflect changes in volcanic activity and exhibit increasing trends prior and during the last major eruptive cycles. Maps of radon emissions indicate that diffuse degassing is operative at Stromboli volcano. Concentrated degassing essentially occurs in the summit area and within a sector proximal to the two major NE trending faults. These sites were chosen for deploying the two real-time stations that are currently operating at Stromboli. In these devices, the 222Rn electronic dosimeters are connected to a radiomodem for wireless data transfer to a receiving station at the volcano observatory. Radon activity, soil temperature and atmospheric pressure data are sampled and instantaneously transferred via web so that they can be checked remotely. Collected time series reveal an overall inverse correlation between radon emissions and seasonal temperature variations. Radon emissions in sectors of diffuse degassing are modulated by tidal forces as well. Radon activities recorded at the summit station, located along the fracture zone where the gas flux is concentrated, are positively correlated with changes in atmospheric pressure and confirm the occurrence of the “atmospheric stack effect”. We finally emphasize that real-time radon monitoring is an innovative technique that may be systematically applied in volcano surveillance.

Comparison between different methodologies for detecting radon in soil along an active fault: The case of the Pernicana fault system, Mt. Etna (Italy)

Three different methodologies were used to measure Radon ( 222Rn) in soil, based on both passive and active detection system. The first technique consisted of solid-state nuclear track detectors (SSNTD), CR-39 type, and allowed integrated measurements. The second one consisted of a portable device for short time measurements. The last consisted of a continuous measurement device for extended monitoring, placed in selected sites. Soil 222Rn activity was measured together with soil Thoron ( 220Rn) and soil carbon dioxide (CO 2) efflux, and it was compared with the content of radionuclides in the rocks. Two different soil–gas horizontal transects were investigated across the Pernicana fault system (NE flank of Mount Etna), from November 2006 to April 2007. The results obtained with the three methodologies are in a general agreement with each other and reflect the tectonic settings of the investigated study area. The lowest 222Rn values were recorded just on the fault plane, and relatively higher values were recorded a few tens of meters from the fault axis on both of its sides. This pattern could be explained as a dilution effect resulting from high rates of soil CO 2 efflux. Time variations of 222Rn activity were mostly linked to atmospheric influences, whereas no significant correlation with the volcanic activity was observed. In order to further investigate regional radon distributions, spot measurements were made to identify sites having high Rn emissions that could subsequently be monitored for temporal radon variations. SSNTD measurements allow for extended-duration monitoring of a relatively large number of sites, although with some loss of temporal resolution due to their long integration time. Continuous monitoring probes are optimal for detailed time monitoring, but because of their expense, they can best be used to complement the information acquired with SSNTD in a network of monitored sites.

Parameterization of Convective Transport in a Lagrangian Particle Dispersion Model and Its Evaluation

AbstractThis paper presents the revision and evaluation of the interface between the convective parameterization by Emanuel and Živković-Rothman and the Lagrangian particle dispersion model “FLEXPART” based on meteorological data from the European Centre for Medium-Range Weather Forecasts (ECMWF). The convection scheme relies on the ECMWF grid-scale temperature and humidity and provides a matrix necessary for the vertical convective particle displacement. The benefits of the revised interface relative to its previous version are presented. It is shown that, apart from minor fluctuations caused by the stochastic convective redistribution of the particles, the well-mixed criterion is fulfilled in simulations that include convection. Although for technical reasons the calculation of the displacement matrix differs somewhat between the forward and the backward simulations in time, the mean relative difference between the convective mass fluxes in forward and backward simulations is below 3% and can therefore be tolerated. A comparison of the convective mass fluxes and precipitation rates with those archived in the 40-yr ECMWF Reanalysis (ERA-40) data reveals that the convection scheme in FLEXPART produces upward mass fluxes and precipitation rates that are generally smaller by about 25% than those from ERA-40. This result is interpreted as positive, because precipitation is known to be overestimated by the ECMWF model. Tracer transport simulations with and without convection are compared with surface and aircraft measurements from two tracer experiments and to 222Rn measurements from two aircraft campaigns. At the surface no substantial differences between the model runs with and without convection are found, but at higher altitudes the model runs with convection produced better agreement with the measurements in most of the cases and indifferent results in the others. However, for the tracer experiments only few measurements at higher altitudes are available, and for the aircraft campaigns the 222Rn emissions are highly uncertain. Other datasets better suitable for the validation of convective transport in models are not available. Thus, there is a clear need for reliable datasets suitable to validate vertical transport in models.

Sulfur, sea salt, and radionuclide aerosols in GISS ModelE

We simulate a suite of aerosols in the new GISS ModelE GCM: present‐day sulfur species and the natural species sea salt, radionuclides 7Be (stratospheric source), and 210Pb (derived from 222Rn from soils). The natural species are used to test the model and to help diagnose the anthropogenic sulfur species. Model improvements over previous versions include increased vertical resolution, addition of a stratiform dissolved species budget (DSB), better tracer coupling to the boundary layer, and an improved relative humidity‐dependent radiative scheme. The DSB reduces the loads of most soluble species since it increases stratiform precipitation scavenging. We compare the model with extensive surface and aircraft concentration measurements in the troposphere and stratosphere. We compare three different formulations of the 222Rn emissions and find that a scheme with reduced radon flux at high latitudes of the Northern Hemisphere for all seasons gives the best 210Pb results. Although the 222Rn emissions appear to be approximately the right order of magnitude, model 210Pb is too large. Conversely, our 7Be source is too small (since concentrations in the upper troposphere and stratosphere are deficient), while the 7Be surface concentrations are as observed. These radionuclide results suggests that model scavenging (by moist convection) is deficient. Our new model uses increased natural sulfur emissions; however, the DSB causes sulfate to be generally less than observed and indicates a need for additional sulfur oxidation mechanisms. Model radiative forcing for sulfate and sea salt are −0.54 and −1.1 W m−2, respectively. The anthropogenic sulfate forcing is −0.25 W m−2, less than the −0.68 W m−2 in our previous model mainly owing to an 18% decrease in industrial emissions.

Evaluation of the radioactive impact of the phosphogypsum wastes used as amendment in agriculture soils

Some 3×109 kg of phosphogypsum (PG) wastes are annually generated by two fertiliser-production factories in Huelva (south-western Spain). PG has relatively high concentrations of 226 Ra and other radionuclides, with an special concern due to the 222 Rn emissions. These wastes could be used to improve the fertility of agriculture soils in a large former marsh area of the Guadalquivir river. Thus, it is interesting to study the levels and behaviour of natural radionuclides within this system to evaluate the radioactive impact of this amendment. An agronomical test is being conducted by one of the authors in an experimental farm in Lebrija (Seville). The soils are treated with 13 and 26 t ha-1 of PG, 30 t ha-1 of manure. Each treatment was repeated twice and continued for two years with beetroot and cotton plant production. We are measuring 226 Ra (by alpha counting and gamma spectrometry) and U isotopes (by alpha spectrometry and ICP-MS analysis) in drainage waters, soils and vegetal-tissues samples. The PG used in the treatment has 620 ± 70 Bq kg-1 of 226 Ra. The drainage waters have 226 Ra contents similar to those from non-contaminated natural waters, but the uranium concentrations are one order of magnitude higher. Our results are suggesting that the major uranium input comes from the application of phosphate-fertiliser. No significant levels of radionuclides were found in the vegetal tissues.

Test of a northwards-decreasing 222Rn source term by comparison of modelled and observed atmospheric 222Rn concentrations

Model-predicted atmospheric concentrations of 222Rn based on two different 222Rn source terms have been compared with observations in the lower troposphere. One simulation used a globally uniform 222Rn source term from ice-free land surfaces of 1 atom cm−2 s−1; the other assumed a northwards-decreasing source term (linear decrease from 1 atom cm−2 s−1 at 30°N to 0.2 atom cm−2 s−1at 70°N). Zero emissions were assigned to oceans. The northwards-decreasing source term improved predictions at four out of six stations north of 50°N, reducing the mean prediction/observation ratio from 2.8 to 0.87. In the latitudinal band between 30°N and 50°N, the northwards-decreasing source term resulted in systematic under-prediction of atmospheric 222Rn, whereas the uniform source term provided predictions close to observations. Predictions based on the northwards-decreasing source term were significantly (p < 0.01) better than those based on the uniform source term for an averaged vertical 222Rn profile around 44°N, but were not for one around 38°N. The results indicate that a northwards-decreasing source term could be a more realistic representation of actual 222Rn emissions than a uniform 1 atom cm−2 s−1 source term. However, the decrease in 222Rn source strength with increasing latitude might not begin at 30°N but somewhat further north. This hypothesis should be investigated through model-independent means.

Use of radon for evaluation of atmospheric transport models: sensitivity to emissions

We present comparative analyses of atmospheric radon (Rn) distributions simulated using different emission scenarios and the observations. Results indicate that the model generally reproduces observed distributions of Rn but there are some biases in the model related to differences in large-scale and convective transport. Simulations presented here use an off-line three-dimensional chemical transport model driven by assimilated winds and two scenarios of Rn fluxes (atom cm−2 s−1) from ice-free land surfaces: (A) globally uniform flux of 1.0 within ±60° and 0.5 within 60°N–70°N and (B) uniform flux of 1.0 between 60°S and 30°N followed by a sharp linear decrease to 0.2 at 70°N. We considered an additional scenario (C) where Rn emissions for case A were uniformly reduced by 28%. Results show that case A overpredicts observed Rn distributions in both hemispheres. Simulated Northern Hemisphere Rn distributions from cases B and C compare better with the observations, but are not discernible from each other. In the Southern Hemisphere, surface Rn distributions from case C compare better with the observations. We performed a synoptic-scale source—receptor analysis for surface Rn to locate regions with ratios B/A and B/C less than 0.5. Considering the maximum uncertainty in regional Rn emissions of a factor of 2, our analysis indicates that additional measurements of surface Rn, particularly during April-October and north of 50°N over the Pacific as well as Atlantic regions, would make it possible to determine if the proposed latitude gradient in Rn emissions is superior to a uniform flux scenario.

Use of radon for evaluation of atmospheric transport models: sensitivity to emissions

We present comparative analyses of atmospheric radon (Rn) distributions simulated using different emission scenarios and the observations. Results indicate that the model generally reproduces observed distributions of Rn but there are some biases in the model related to differences in large-scale and convective transport. Simulations presented here use an off-line three-dimensional chemical transport model driven by assimilated winds and two scenarios of Rn fluxes (atom cm−2 s−1) from ice-free land surfaces: (A) globally uniform flux of 1.0 within ±60¼ and 0.5 within 60¼N–70¼N and (B) uniform flux of 1.0 between 60¼S and 30¼N followed by a sharp linear decrease to 0.2 at 70¼N. We considered an additional scenario (C) where Rn emissions for case A were uniformly reduced by 28%. Results show that case A overpredicts observed Rn distributions in both hemispheres. Simulated Northern Hemisphere Rn distributions from cases B and C compare better with the observations, but are not discernible from each other. In the Southern Hemisphere, surface Rn distributions from case C compare better with the observations. We performed a synoptic-scale source—receptor analysis for surface Rn to locate regions with ratios B/A and B/C less than 0.5. Considering the maximum uncertainty in regional Rn emissions of a factor of 2, our analysis indicates that additional measurements of surface Rn, particularly during April-October and north of 50¼N over the Pacific as well as Atlantic regions, would make it possible to determine if the proposed latitude gradient in Rn emissions is superior to a uniform flux scenario.

Validation and intercomparison of wet and dry deposition schemes using 210Pb in a global three‐dimensional off‐line chemical transport model

We have used 210Pb, a tracer originating from the radioactive decay of 222Rn emitted from soils, to validate different wet and dry deposition schemes in our global three‐dimensional off‐line chemical transport model, TOMCAT. We have tested two different parameterizations for the dry deposition, one with the turbulent exchange in the boundary layer and one without. When dry deposition is linked to the boundary layer scheme, the model shows the ability to resolve shallow mixing depths in winter with enhanced lifetimes and concentrations of surface aerosol. Three conceptually different wet deposition schemes have been implemented and tested in TOMCAT. In the first, where wet removal is assumed to be proportional to the local gradient of the specific humidity, the model has a global mean bias for the surface concentrations of −40%. Using this scheme, the observed surface concentrations are seriously underpredicted, and most of the aerosol burden is scavenged within the boundary layer. In the second scheme, where scavenging is parameterized proportional to the model‐derived total precipitation rate (large scale and convective), the model exhibits a +26% bias. The concentrations are overpredicted, especially in continental areas as this scheme fails to capture the coupling between vertical transport and rainout. In the third scheme, wet removal is coupled with the vertical transport inside convective clouds. The model then shows the best performance with only a −4% bias for the concentrations. Furthermore, other regional discrepancies between model and observations point to a variability in 222Rn emissions, which was not taken into account with our simple 222Rn emission scenario, and also to anomalies in our model‐derived precipitation rate. The aerosol residence times are realistic only when the wet removal schemes use the precipitation rate rather than the specific humidity. The dry subtropical and polar regions can be captured with lifetimes at 500 hPa of more than 50 days whereas in regions of high precipitation the lifetimes are less than 5 days.

Radon 222 simulations as a test of a three‐dimensional regional transport model

Radon 222 distributions during the 1993 North Atlantic Regional Experiment are simulated with the National Oceanic and Atmospheric Administration Aeronomy Laboratory three‐dimensional regional transport model. The model domain covers the western part of the North Atlantic Ocean and part of the eastern United States and Canada. It horizontally elongates 4200 km in the east‐west and north‐south directions and vertically extends from the surface to 50 mbar. The model simulates emissions, transport, and radioactive decay of 222Rn. Advection, cloud transport, mixing in the planetary boundary layer, and diffusion are simulated and the emissions, boundary, and initial conditions are parameterized. The model results are analyzed to study the ability of the model to simulate 222Rn distribution in the troposphere. The analysis indicates that 222Rn simulations near the surface are dominated by emissions. At altitudes from &lt;1 km to ∼6 km the simulations are noticeably influenced by the side boundaries and the influence increases with increasing altitude. Radon 222 simulations in the upper troposphere (z &gt;6 km) are dominated by side boundary conditions and the wind field. The impact of top boundary on 222Rn simulations is negligible provided the top is specified at an altitude well above the tropopause. Cloud mixing is important in the vertical transport of 222Rn from the surface to the free troposphere. Cloud effect is significant in 222Rn distributions at grid columns within or near which there are abundant clouds. The mean effect of cloud mixing cannot be appropriately represented by contrasting large‐scale or long‐term average 222Rn distributions simulated in cases with and without cloud mixing. Surface pressure fluctuation has substantial influence on 222Rn emission and concentration variabilities, but this effect is restricted to altitudes near the surface. The model‐simulated 222Rn concentrations are compared with measurements made onboard the U.S. Department of Energy Gulfstream aircraft based at Halifax, Nova Scotia, to evaluate the quality of the simulations. The comparison indicates that the simulations and observations are usually within a factor of 2 of one another and significantly correlated with each other. The simulations are capable of capturing high 222Rn concentrations observed in continental plumes.

Radon emissions from mud volcanoes in northern Italy: Possible connection with local seismicity

Data concerning Radon emission in waters filling mud volcanoes of Northern Apennines (Northern Italy) sampled from 1986 until 1989 have been analyzed. Possible connections between shallow environmental conditions and Rn emission from mud volcanoes have been explored. A linear relationship between air temperature and Rn count rates has been determined. After the removal of temperature related Rn variations, a significant correlation has been pointed out between anomalous spike‐like Rn emissions at one of the station considered and the occurrence of low magnitude (M&lt;4.5) local earthquakes.

222Rn Emission Flux and Soil-Atmosphere Interface: Comparative Analysis of Different Measurement Techniques

Abstract Radon emission flux at the ground-atmosphere interface is one of the measurements commonly made for environmental purposes and on prospective mining sites. There are a number of ways of making such measurements. Generally an 'accumulation' technique is used. This method consists in determining the radon activity at a given time, inside a container placed on the ground with one side open, facing downward. The radon activity is determined by sampling the air inside the confinement system with a scintillation flask. The purpose of this work was to simplify this method by using other radon activity measurement techniques. The flux measurements made by the usual method, used as reference (spot sampling), were compared with those made using a silicon detector (continuous measurement) and with a solid trace detector (integrated measurement). For the latter two methods, a correction factor is applied to obtain the real value of the 222Rn emission flux yielded by the reference method.

Neoplastic Transformation Dose Response of Oncogene-Transfected Rat Embryo Cells by Gamma Rays or 6 MeV Alpha Particles

We measured a dose-response relationship for induction of neoplastic transformation by 6 MeV alpha particles and 137Cs gamma rays in REC:myc and REC:ras cells, that is, rat embryo cells (REC) transfected with the c-myc or the Ha-ras oncogenes. The 6 MeV alpha particles simulated 222Rn emissions for risk assessment relative to low-LET radiations. The dose of gamma rays was approximately twice that of alpha particles for a neoplastic transformation frequency of 10(-3). The survival of the REC cells containing oncogenes was comparable to that of the commonly used C3H 10T1/2 cells for the same dose, but the former were more refractory to radiation-induced neoplastic transformation. Neoplastic transformation frequency measured in REC cells was 3 times lower than those typically measured in C3H 10T1/2 cells at a gamma-ray dose of 6 Gy, and 5-10 times lower at an alpha-particle dose of 3 Gy.

Recent sedimentary histories of shallow lakes in the guatemalan savannas

Shallow basins in the savannas of Peten, Guatemala filled with water after 305±55 BP (calibrated age+1430–1660 AD). Aguadas Chimaj and Chilonche possess dilute waters and iron-rich, clayey sediments that are poor in Ca and Mg, reflecting the highly weathered nature of riparian soils. Low 210Pb flux rates to Chimaj (0.085 pCi cm-2 yr-1) and Chilonche (0.134 pCi cm-2 yr-1) are attributed to low 222Rn emission rates from the nearby Caribbean Sea. Mean sediment accumulation rates in Chimaj and Chilonche for the past 150 years are 0.015 g cm-2 yr-1 and 0.047 g cm-2 yr-1 respectively. Forest expansion after 305 BP is documented in pollen profiles from the small aguadas and larger Lake Oquevix. Regional reforestation postdates the 9th century Classic Maya collapse and coincides with indigenous depopulation that was a consequence of European intrusion that began in the early 1500s. The timing of forest regrowth indicates the importance of historical anthropogenic factors in controlling Peten's vegetation. Nevertheless, other sedimentological lines of evidence (e.g. lithology, algal remains and charcoal particles) suggest that changing climate and/or local hydrology may have played a role in the reforestation process.

Variations of electric resistance and H2 and Rn emissions of concrete blocks under increasing uniaxial compression

Electric resistance and emissions of hydrogen and radon isotopes of concrete (which is somewhat similar to fault-zone materials) under increasing uniaxial compression were continuously monitored to check whether they show any pre- and post-failure changes that may correspond to similar changes reported for earthquakes. The results show that all these parameters generally begin to increase when the applied stresses reach 20% to 90% of the corresponding failure stresses, probably due to the occurrence and growth of dilatant microcracks in the specimens. The prefailure changes have different patterns for different specimens, probably because of differences in spatial and temporal distributions of the microcracks. The resistance shows large co-failure increases, and the gas emissions show large post-failure increases. The post-failure increase of radon persists longer and stays at a higher level than that of hydrogen, suggesting a difference in the emission mechanisms for these two kinds of gases. The H2 increase may be mainly due to chemical reaction at the crack surfaces while they are fresh, whereas the Rn increases may be mainly the result of the increased emanation area of such surfaces. The results suggest that monitoring of resistivity and gas emissions may be useful for predicting earthquakes and failures of concrete structures.

Radon-Thoron estimation using LR-115 plastic track detector

LR-115 plastic track detector and a Radon-Thoron discriminator has been used to estimate the radon (Rn) and thoron (Tn) contents in the soil of Guru Nanak Dev University Campus area. Track production rates in the soil at different depths have been studied. Uranium estimation in the soil samples from the experimental site have also been made to establish some correlation with Rn emission. Rn-emanation rates from the plants growing around the experimental site have also been studied using LR-115 plastic track detector. Plant leaves have been found to emanate more Rn than stems.

Lung cancer and phosphates

In the United States, counties with phosphate mining or processing facilities frequently also have significantly elevated rates of mortality from lung cancer. To deduce this result, the locations of areas having high mortality rates from lung cancer have been compared with those containing phosphate deposits, mines, or processing plants. The results for both white and nonwhite populations show correlations which are improbable by pure chance. They should be examined on a site-by-site basis to establish whether 222Rn emissions from 226Ra are a significant factor in the elevated cancer mortality.

Origin of thermal waters on the basis of their radioisotopic content

The content of the isotopes of U, Ra, Th and also Rn 222, Ac 227 and Pb 210 was investigated in the waters of active volcanism (Kamchatka, Kuril Islands) and in the thermal waters of neovolcanic regions (Caucasus). The content of radioisotopes in the condensates of the volcanic vapours is very like that of the depth gases. Here the average content of radioisotopes is U 2.5 × 10 −7 g/l, Ra 1.0 × 10 −13 g/l, Pb 210 8 × 10 −15 g/l. The Ra/Rn (or U/Rn) varies from 10 −3 to 10 −5 (activity units). In the fumarole waters the content of U and Pb 210 diminished by several times (dilution in the meteoric waters) and the content of Ra by tens of times (precipitation of the elements from the sulphatic waters). The average ratios: U 234/U 238 = 1.3; Io/Th = 1.05; RdTh/Th = 2.0; MsTh/Ra = 10; Pb 210/Ra 226 ≥ 30 are increased. The same results are obtained in the fumarole minerals too. The Pu 239 indicates the existence of depth matter. The thermal waters (Causcasus) are distinguished by increased value of U 234/U 238 (the average 2.0, but in some cases reaches to 3.5). The content of shortlived isotopes of Th and Ra can be very high (RdTh/Th = 16 and ThX/MsTh = 105). This indicates the proximity of the formation region, the recent age of the water and the absence of contamination from waters of different genesis. The content of Ra 226 is small and U 238/Rn decreases as compared to volcanic waters. It means that the Rn emission from the rocks is here less essential than in active volcanism rocks. The time of circulation of the gas vapour flows of the volcanoes can be estimated on the Rn/Ra ratio as 10 ÷ 100 days, and for thermal waters as much as hundreds of years. The difference of the radiochemical parametres allows us to determine the genesis of thermal waters.