Emanation Coefficient Research Articles

Environmental evaluation of natural radioactivity in soil near a lignite-burning power plant in Turkey

Natural radionuclides are released into the environment together with fly ash from the coal-burning power plant and cause an increase in the natural radioactivity in environmental samples. The study concerns to the evaluation the influence of Kangal lignite-burning power plant (LBPP) with a power of 457 MWe, which has been in operation since 1989, on natural radionuclide a concentration in surface soil samples around it. Activity concentrations of natural radionuclides (226Ra, 232Th, 40K and 222Rn) in the soil samples, and emanation coefficient (EC) and mass (ERM) and surface (ERS) exhalation rate of radon were determined by using a gamma-ray spectrometer with an HPGe detector. The average values of 226Ra, 232Th, 40K and 222Rn, EC, ERM and ERS were found as 37±5, 17±3, 222±30Bqkg−1 and 9±1kBqm−3, 12%, 12.1 µBq kg−1 s−1 and 7.1mBqm−2 s−1, respectively. Absorbed gamma dose rate in outdoor air and the corresponding effective dose rate from external exposure and excess lifetime cancer risk were estimated to evaluate radiological hazards for human population. The results revealed that the Kangal LBPP has caused a small increment in 226Ra concentration in the studied area. No influence was observed for 232Th and 40K.

Radon emanation coefficients of several minerals: How they vary with physical and mineralogical properties

The escape rates of radon gas from rocks and minerals are of great relevance to many branches of geosciences, and it is, thus, important to understand the physical and mineralogical properties that control radon emanation rates. Mechanisms of radon loss from minerals have direct bearing on the reliability of U-Pb and U-Th-He geochronology. Fourteen minerals from three different mineral groups and with localities spanning three continents were selected for this study. The radon emanation coefficients (REC) for each mineral were measured as a function of grain size, temperature, 238 U and 232 Th activities, total absorbed α-dose, density, and mineral melting temperature. The measured 238 U and 232 Th activities ranged from 0.01 to 6487 Bq/g and from below detection limit to 776 Bq/g, respectively. The REC values for unheated, pulverized samples ranged from 0.083 to 7.0%, which is comparable to previously reported ranges (except for zircon). An inverse correlation between grain size and REC was observed. Full annealing of fission tracks resulted in an overall decrease in REC values, suggesting that nuclear tracks could possibly act as conduits for radon release. While activity, α dose, density, and melting temperatures are not strongly correlated with REC values, it was observed that minerals with high melting points (≥1400 °C) have lower REC values, most likely due to inhibition of radon release by compact crystal-lattice structures. This is the first attempt, to our knowledge, to correlate REC values with melting temperature, and this study reports six minerals for which no REC values have been previously reported.

Effective radium-226 concentration in meteorites

The analysis of noble gases in meteorites provides constraints on the early solar system and the pre-solar nebula. This requires a better characterization and understanding of the capture, production, and release of noble gases in meteorites. The knowledge of transfer properties of noble gases for each individual meteorite could benefit from using radon-222, radioactive daughter of radium-226. The radon-222 emanating power is commonly quantified by the effective radium-226 concentration (ECRa), the product of the bulk radium-226 concentration and of the emanation coefficient E, which represents the probability of one decaying radium-226 to inject one radon-222 into the free porous network. Owing to a non-destructive, high-sensitivity accumulation method based on long photomultiplier counting sessions, we are now able to measure ECRa of meteorite samples, which usually have mass smaller than 15g and ECRa<0.5Bqkg−1. We report here the results obtained from 41 different meteorites, based on 129 measurements on 70 samples using two variants of our method, showing satisfactory repeatability and a detection limit below 10−2Bqkg−1 for a sample mass of 1g. While two meteorites remain below detection level, we obtain for 39 meteorites heterogeneous ECRa values with mean (min–max range) of ca. 0.1 (0.018–1.30)Bqkg−1. Carbonaceous chondrites exhibit the largest ECRa values and eucrites the smallest. Such values are smaller than typical values from most terrestrial rocks, but comparable with those from Archean rocks (mean of ca. 0.18Bqkg−1), an end-member of terrestrial rocks. Using uranium concentration from the literature, E is inferred from ECRa for all the meteorite samples. Values of E for meteorites (mean 40±4%) are higher than E values for Archean rocks and reported values for lunar and Martian soils. Exceptionally large E values likely suggest that the 238U-226Ra pair would not be at equilibrium in most meteorites and that uranium and/or radium are most likely not uniformly distributed. ECRa of meteorites is correlated with E and seems to mainly reflect the gas permeability of the meteorite, which could be one important property, preserved in the meteorite, of its parent body, characterizing its history in space, possibly modified by alteration, shock metamorphism, and eventually weathering on Earth. Larger radon emanation values are associated with larger concentrations of the heaviest noble gases (argon, krypton, xenon), and larger 20Ne/22Ne and 36Ar/38Ar ratios, suggesting Earth’s atmosphere contamination or solar wind implantation, and probably a similar carrier phase such as Q phase. An unclear correlation is observed with 40Ar, which may rule out a purely radiogenic effect on radon emanation. Thus, larger radon emanation suggests a larger capacity of collecting solar and terrestrial gases, which should imply higher loss of gases generated in the meteorite and larger dispersion of Pb/U ratios for age determination. This study provides the first quantification of natural radon-222 loss from meteorites and opens promising perspectives to quantify the relationship between pore space connectivity and the transfer properties for noble gases in meteorites and other extraterrestrial bodies.

Study of a remediated coal ash depository from a radiological perspective

Coal-fired power plants play a significant role in the production of electricity. The Ra-226 concentration of coals mined in the Ajka region can reach up to 3000 Bq/kg. This study focuses on the effects of a Hungarian (Ajka) remediated coal ash depository on the environment and the effectiveness of the cover layer. During the remediation, a method patented in Hungary was used, in which the upper layer of the depository, which had settled like concrete, was ploughed and mixed with woodchips before being planted with vegetation.The gamma dose rate H*(10) of the depository and its vicinity was measured using Automess 6150AD-b at 32 points, surface Rn-222 exhalation at 19 points and air radon concentration at 34 points; at 32 points, soil gas radon content was measured with AlphaGUARD and soil permeability with RADON-JOK. The nuclide content of nine samples was determined using an HPGe gamma spectrometer and their Rn-222 exhalation rates were measured using the AlphaGUARD.H*(10) was 290 (130–525) nSv/h at the covered depository; CRa-226 was 1997 Bq/kg, 960 Bq/kg and 104 Bq/kg for the ash, cover layer and background soil respectively. CRn-222 in the soil was 25–161 kBq/m3, and soil gas permeability K was between 6.4E-13 and 1.80E-11 m2. The radon exhalation of the uncovered and covered depository was 259–1100 mBq/m2s. The exhalation and emanation coefficients of the samples were 0.05–0.32 mBq/kgs and 8–22%. The effects of vegetation on the migration of radon were also examined. The results show that the Ajka coal ash depository involves higher radiological risk than that reported by previously published studies on depositories. The applied cover layer halved the field radon exhalation; in addition, the vegetation reduced the convective airflow and, with this, the migration of Rn.

Особливості процесів міграції природних радіонуклідів в підземних водах при ліквідації вугільних шахт Північно-Східного Донбасу

The article is analyzed features of processes migration of natural radionuclides in the underground water at the liquidation of coal mines of North-Eastern Donbass on the example of mine Proletarian and Svitlichanskyi of water intake. It is revealed, that exactly 222 Rn is the most widespread source of natural radioactivity both on the whole in Ukraine and in the Donbass. It is noted that the closure of coal enterprises and avtoreabilitatsionny rise of underground water that accompanies them, has a regional scale. Analysis of hydrogeological conditions and processes occurring in the underground environment, speaks of the danger of radioactive contamination 226 Ra and 222 Rn of the underground water. The results of the ecological and radiological research areas abandoned mines lead to the conclusion that on the whole territory of the North-Eastern Donbass radiation situation is normal. At the same time are fixed local areas with high concentration of natural radionuclides present in the zones of influence of the major tectonic disturbances (Severodonetskyi, Chehirovskyi and Diagonal thrusts). It is said that the studies in the Almazno-Marevskyi geological and industrial district of the North-Eastern Donbass indicates the presence of a high content of the natural radionuclides ( 226 Ra, 232 Th, 40 K, 222 Rn) in the mine atmosphere, soil, surface and groundwater, as well as in the waste coal located at the territory of the former mine fields of mines, Luganskaya, Proletarian and G. Kapustin. It is shown that the main factors determining migration of the natural radionuclides in the underground water are the way they are received into the aquifer and the physical and the chemical properties of both the underground water and the rock mass. It is established, 222 Rn concentration in the water is depends on the concentration of the parent radioactive elements in the coal-bearing strata washed it, the emanation coefficient, fracture rock mass and velocity of underground water flow. Besides the presence of natural radionuclides in the underground water of the water intakes also is noted the high content of Cl, Mn, Fe. It is noted that filling out space mines with highly salinity water downstream, deep aquifers carbon, inevitably leads decrease in quality (increase salinity, occurrence heavy metals, natural radionuclides, etc.) of the upper cretaceous underground water aquifer exploited Svitlichanskyi water intake. At the same time fixation 222 Rn in the water wells Svetlichanskyi water intake is associated with a pulling up of pollution the water intake by funnel depression. In conclusion, in the area of sanitary protection of the water intake Svitlichanskyi and adjacent by Proletarian mine field is proposed to conduct a comprehensive monitoring of the geological environment, including constant monitoring and control of the hydro-geological and geomechanical processes, as well as the migration of mine gas and 222 Rn.

A study of thoron exhalation from monazite-rich beach sands of High Background Radiation Areas of Kerala and Odisha, India

Thoron exhalation from earth’s surface is the most important source of environmental thoron. The High Background Radiation Areas (HBRAs) of Kerala and Odisha in India have beaches with sands enriched with monazite, an ore of thorium, making it unique for study of thoron exhalation. In the present study, in situ measurement of thoron exhalation was carried out to map the thoron exhalation rate over complete coastline of the known HBRAs. New experimental setups for measurement of thoron surface exhalation and thoron mass emanation were developed and validated. The exhalation measurements were carried out on beaches of Chavara–Neendakara (CN) area of Kerala and Chatrapur (CH) region of Odisha. The beaches of the Kerala region showed an average thoron exhalation rate of 5.95 ± 2.98 Bq m−2s−1, which for the beaches of Chatrapur area of Odisha was 2.77 ± 0.96 Bq m−2s−1. The external gamma exposure rate was also measured at these locations, and it was observed to be well correlated with in situ thoron exhalation rate. Sand samples were collected from ten of the measurement locations and analyzed in the laboratory for a further understanding of thoron exhalation process in the beach sand. Measurement of specific thoron mass emanation rate, specific 224Ra content and thoron emanation coefficient was taken for the samples. A good correlation was found between in situ thoron exhalation rate and specific thoron mass emanation rate. The effective thoron diffusion length was determined by using the measured parameters in the UNSCEAR radon exhalation model and was found to be nearly constant with a value of 2.2 ± 0.36 cm. This study shows that in spite of very high thorium content (500–1000 times) as compared to normal fine soils, the thoron exhalation from the HBRA beach sands was only 4–12 times higher due to very low emanation coefficient, about 1000 times smaller than that for normal soils.

Effective radium-226 concentration in rocks, soils, plants and bones

Abstract Effective radium-226 concentration, EC Ra , is the product of radium activity concentration, C Ra , multiplied by the emanation coefficient, E , which is probability of producing a radon-222 atom in the pore spaces. It is measured by accumulation experiments in the laboratory, achieved routinely for a sample mass &gt;50 g using scintillation flasks to measure the radon concentration. We report on 3370 EC Ra values obtained from more than 11 800 such experiments. Rocks ( n =1351) have a mean EC Ra value of 1.9±0.1 Bq kg −1 (90% of data in the range 0.11–35 Bq kg −1 ), while soils ( n =1524) have a mean EC Ra value of 7.5±0.2 Bq kg −1 (90% of data between 1.4 and 28 Bq kg −1 ). Using this large dataset, we establish that the spatial structure of EC Ra is meaningful in geology or sedimentology. For plants ( n =85), EC Ra is generally &lt;1 Bq kg −1 , but values of larger than 10 Bq kg −1 are also observed. Dedicated experiments were performed to measure emanation, E , in plants, and we obtained values of 0.86±0.04 compared with 0.24±0.04 for sands, which leads to estimates of the radium-226 soil-to-plant transfer ratio. For most measured animal bones ( n =26), EC Ra is &gt;1 Bq kg −1 . Therefore, EC Ra appears essential for radon modelling, health hazard assessment and also in evaluating the transfer of radium-226 to the biosphere.

Estimation of the radon production rate in granite rocks and evaluation of the implications for geogenic radon potential maps: A case study in Central Portugal

The goal of this study was to estimate radon gas production rate in granitic rocks and identify the factors responsible for the observed variability. For this purpose, 180 samples were collected from pre-Hercynian and Hercynian rocks in north and central Portugal and analysed for a) 226Ra activity, b) radon (222Rn) per unit mass activity, and c) radon gas emanation coefficient. On a subset of representative samples from the same rock types were also measured d) apparent porosity and e) apparent density. For each of these variables, the values ranged as follows: a) 15 to 587Bqkg-1, b) 2 to 73Bqkg-1, c) 0.01 to 0.80, d) 0.3 to 11.4 % and e) 2530 to 2850kgm-3. Radon production rate varied between 40 to 1386Bqm-3h-1. The variability observed was associated with geologically late processes of low and high temperature which led to the alteration of the granitic rock with mobilization of U and increase in radon 222Rn gas emanation. It is suggested that, when developing geogenic radon potential maps, data on uranium concentration in soils/altered rock should be used, rather than data obtained from unaltered rock.

Novel method of measurement of radon exhalation from building materials

In the era of the energy saving policy (i.e. more air tight doors and windows), the radon exhaled from building materials tends to increase its concentration in indoor air, which increases the importance of the measurement of radon exhalation from building materials. This manuscript presents a novel method of the radon exhalation measurement using only a HPGe detector or any other gamma spectrometer. Comparing it with the already used methods of radon exhalation measurements, this method provides the measurement of the emanation coefficient, the radon diffusion length and the radon exhalation rate, all within the same measurement, which additionally defines material's radon protective properties. Furthermore it does not necessitate additional equipment for radon or radon exhalation measurement, which simplifies measurement technique, and thus potentially facilitates introduction of legal obligation for radon exhalation determination in building materials.

Evaluation of radiological hazards associated with the uses of marble and ceramic as decorative building materials in Egypt

Radon concentrations of 20 samples of marble and ceramic were measured using AlphaGuard and varied from 36.02 ± 2.89 to 614.59 ± 99.40 Bq m−3 with a mean value of 139.12 ± 11.44 Bq m−3. Radon emanation coefficient and exhalation rate were also calculated. Moreover, radiation dose of released radon was calculated using two models, showing good agreement. Its value was varied from 6.3 ± 0.52 to 76.23 ±3.82 μSv year−1 with a mean value of 23.20 ± 1.54 μSv year−1. The results implied that radiation dose was less than safety limit of 1 mSv year−1. Therefore, the selected marble and ceramic types could be safely used as decorative building materials.

Radon exhalation study of manganese clay residue and usability in brick production

The reuse of by-products and residue streams is an important topic due to environmental and financial aspects. Manganese clay is a residue of manganese ore processing and is generated in huge amounts. This residue may contain some radionuclides with elevated concentrations. In this study, the radon emanation features and the massic exhalation rate of the heat-treated manganese clay were determined with regard to brick production. From the manganese mud depository, 20 samples were collected and after homogenization radon exhalation characteristics were determined as a function of firing temperatures from 100 to 750 °C. The major naturally occurring radionuclides 40K, 226Ra and 232Th concentrations were 607 ± 34, 52 ± 6 and 40 ± 5 Bq kg−1, respectively, comparable with normal clay samples. Similar to our previous studies a strong correlation was found between the internal structure and the radon emanation. The radon emanation coefficient decreased by ∼96% from 0.23 at 100 °C to 0.01 at 750 °C. The massic radon exhalation rate of samples fired at 750 °C reduced by 3% compared to samples fired at 100 °C. In light of the results, reusing of manganese clay as a brick additive is possible without any constraints.

Radiological and material characterization of high volume fly ash concrete

The main goal of research presented in this paper was the material and radiological characterization of high volume fly ash concrete (HVFAC) in terms of determination of natural radionuclide content and radon emanation and exhalation coefficients. All concrete samples were made with a fly ash content between 50% and 70% of the total amount of cementitious materials from one coal burning power plant in Serbia. Physical (fresh and hardened concrete density) and mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity) of concrete were tested. The radionuclide content (226Ra, 232Th and 40K) and radon massic exhalation of HVFAC samples were determined using gamma spectrometry. Determination of massic exhalation rates of HVFAC and its components using radon accumulation chamber techniques combined with a radon monitor was performed. The results show a beneficial effect of pozzolanic activity since the increase in fly ash content resulted in an increase in compressive strength of HVFAC by approximately 20% for the same mass of cement used in the mixtures. On the basis of the obtained radionuclide content of concrete components the I -indices of different HVFAC samples were calculated and compared with measured values (0.27–0.32), which were significantly below the recommended 1.0 index value. The prediction was relatively close to the measured values as the ratio between the calculated and measured I-index ranged between 0.89 and 1.14. Collected results of mechanical and radiological properties and performed calculations clearly prove that all 10 designed concretes with a certain type of fly ash are suitable for structural and non-structural applications both from a material and radiological point of view.

Mechanisms of radon loss from zircon: Microstructural controls on emanation and diffusion

Understanding how radon escapes from minerals is important for many fields in Earth science, yet few studies have focused on the mechanisms for radon escape. We measured radon emanation rate and radon loss upon heating for crushed aliquots of three large zircon crystals from three localities: Mud Tank (Australia), Bancroft (Canada), and Malawi (Africa). Our study, in conjunction with published data, shows that the room temperature radon emanation coefficient (REC) varies over 5 orders of magnitude in zircon. For low U zircon, Mud Tank, there are variations in REC that appear to be related to annealing at different temperatures, possibly due to annealing of fission tracks, however, all REC values for Mud Tank zircon are within error of one another. Bancroft and Malawi zircons have higher U content and do not show any systematic relationship of REC to annealing temperature. Results from Mud Tank zircon suggest that partial annealing of fission tracks decreases REC, but when all fission tracks are annealed REC reaches a maximum. REC in zircons with high U content, Bancroft and Malawi, is slightly higher than in zircon with lower U, although results are within error. Results of measurements of radon loss upon heating suggest that radon diffusion is slow, ∼30% of the radon is lost during heating at 975°C for 48h. Samples heated a second time yield less fractional radon loss, ∼10%, suggesting that diffusion parameters are changed during heating at temperatures ⩾975°C, which is likely the result of annealing of radiation damage. Diffusion parameters calculated from the fractional loss experiments reflect diffusion in highly radiation damaged or metamict zircons. Our results indicate that internal microstructures in zircon, such as fission tracks and alpha-radiation damage, influence radon escape for diffusion and recoil mechanisms, and hence if these effects can be further characterized, measurements of 222Rn escape have the potential to be useful for probing the internal structure of zircon, and other U-bearing minerals.

NORM, radon emanation kinetics and analysis of rocks-associated radiological hazards

Analysis of naturally occurring radioactive material (NORM) and environmental (radiological) hazard associated with radionuclides in rocks from northeastern Nigeria was carried out and the results are presented. NORMs analysis on rock samples was undertaken with gamma-ray spectroscopy, while radon isotopes were analyzed using an electric radon measurement device (RAD 7). Activity concentration (Bq kg−1) of 226Ra, 232Th and 40K ranges from 11.4 ± 2.6 to 74.6 ± 4.8, 26.6 ± 0.8 to 183.4 ± 3 and 30.1 ± 4.6 to 1120.3 ± 16.4, respectively. Ranges for annual effective dose (mSv) are 0.03–0.20; radium equivalent (Bq kg−1) is 5.7.33–358.36; external hazard index is 0.16–0.99; 222Rn and 220Rn exhalation rates (Bqm−3 h−1) are 2.60–6.25 and 0.50–7.10, respectively. For radon emanation coefficient, the working month level and related dosages ranges are 0.012–0.058, 0.25–0.00 and 1.38–3.30 mSv, respectively. The results reveal that the possible radionuclides enrichment in the rocks is potentially an environmental (radiation) hazard to the inhabitants of the area.

The national survey of natural radioactivity in concrete produced in Israel

The main goal of the current survey was to collect the results of the natural radiation tests of concrete produced in the country, to analyze the results statistically and make recommendations for further regulation on the national scale.Totally 109 concrete mixes produced commercially during the years 2012–2014 by concrete plants in Israel were analyzed. The average concentrations of NORM did not exceed the values recognized in the EU and were close to the values obtained from the Mediterranean countries such as Greece, Spain and Italy.It was also found that although the average value of the radon emanation coefficient of concrete containing coal fly ash (FA) was lower, than that of concrete mixes without FA, there was no significant difference between the indexes of both total radiation (addressing gamma radiation and radon together), and gamma radiation only, of the averages of the two sub-populations of concrete mixes: with and without FA.

Assessment of natural radioactivity in fertilizers and phosphate ores in Egypt

Radionuclide concentrations of uranium (238U), thorium (232Th) and potassium (40K) maintained in 10 phosphate ore and 5 fertilizer samples were measured using a high-purity germanium detector. The concentrations of these radionuclides in the phosphate ore samples were relatively high for 226Ra at 871.37±91.90Bqkg−1 and relatively low for 232Th and 40K at 19.21±2.42Bqkg−1 and 176.06±17.66Bqkg−1, respectively. The concentrations of these radionuclides were low in the fertilizer samples. The radiological hazards of the radium equivalent activity (Raeq), external (Hex) and internal (Hin) indices and annual effective dose due to the presence of these radionuclides in the investigated samples were calculated. The released radon from the selected samples was measured using the Alpha Guard radon monitor. Subsequently, the radon emanation coefficient and its exhalation rate were calculated.

Prototype of a primary calibration system for measurement of radon activity concentration

To calibrate measurement devices for monitoring the activity concentration of 222Rn in air, a prototype of a calibration facility is tested using a solid 226Ra source and a high-purity germanium (HPGe) detector. An emanation box was mounted on the detector for online gamma measurements. Inside this box, a 32.8kBq ±3% 226Ra standard source was placed. An AlphaGUARD control radon monitor was connected to the emanation box with a pumping air system in an open flow mode as a reference monitor. The emanation coefficient of the source was controlled online by comparing the gamma activity of 214Bi (Eγ=609.3keV), progeny of 226Ra, to that of the calibration source. A standard 137Cs source, installed within the emanation box, was used as a reference for gamma spectroscopy using the HPGe detector, with a total systematic error of 4% and a random error less than 2%. The ratio between gamma measurements and AlphaGUARD was 0.94±0.4; which is within the 9% uncertainties of AlphaGUARD calibration.

Parameter Ranking System of Indoor Radon Concentration in South Korea, Case Studies: Dokdo Island, Yang Pyeong and Nae Gi

Indoor Radon concentration (IRC) is among the emerging environmental and health issues in Republic of Korea. Due to lack of epidemiological studies and insufficient public awareness about Radon, effective parameter ranking system is required to establish protocols for future field sampling and settlement construction. This research propose the IRC parameter ranking system based on field measurements and laboratory experiments. Dokdo Island, Yang Pyeong and Nae Gi were selected as the case studies in South Korea. The Radon transport equations and statistical analyses are modelled with Simulink and Matlab. IRC model accounts for exhalation of Radon from soil, building material and outdoor air and also considers the major mitigation methods like ventilation, air cleaners and filtration. The PAWN sensitivity analysis method has been applied to determine the sensitivity of each parameter. The results indicates that soil gas radon concentration, radium concentration, emanation coefficient and ventilation rate have the most dominant role on IRC. Based on these results, field sampling patterns and indoor mitigation strategies can be established for restricted access areas and probabilistic studies.

Radiometric analysis of volcanic tuff stones used as ornamental and structural building materials in Turkey and evaluation of radiological risk

Volcanic tuff stones are widely used to coat the interior and exterior surfaces of buildings for ornamental purposes in the construction industry in Turkey, and are also used as structural material in the construction of masonry buildings, especially in the Cappadocia region, which is a popular tourist destination. In this study, seventy-six volcanic tuff stone samples collected from different quarries located in different geographical regions in Turkey were surveyed for radiometric analysis, and the radiological risk to human health caused by ionizing radiation from natural radionuclides in the volcanic tuff stone samples was evaluated. The activity concentrations of 238 U, 232 Th, 226 Ra and 40 K analyzed in volcanic tuff stone samples were very variable, ranging from 3 to 389, 8 to 401, 2 to 263 and 99 to 2107 Bq kg -1 , respectively. The emanation coefficient and mass exhalation rate of 222 Rn measured for the volcanic tuff samples ranged from 2 to 68% with an average of 34%, and 1 to 194 μ Bq kg -1 s -1 with an average of 43 μ Bq kg -1 s -1 , respectively. The external (gamma) and internal (alpha) hazard indices, indoor absorbed gamma dose rate and the corresponding annual effective dose were estimated to evaluate the potential radiological risk to human health. The results showed that all of the surveyed volcanic tuff stone samples can be used as covering building materials for ornamental or insulating covering purposes. However, the use of some volcanic tuff stone samples as structural building materials should be restricted.

Escape of unradiogenic osmium during sub-aerial lava degassing: Evidence from fumarolic deposits, Piton de la Fournaise, Réunion Island

This study presents new Re–Os isotope and elemental data in gas condensates and corresponding lavas in order to examine the geochemical behavior of these two elements during magma degassing at Piton de la Fournaise, Réunion Island.Gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca. 100°C include Na–K sulfate (aphthitalite), Na sulfate (thenardite), Ca–Cu sulfate (e.g. gypsum), Ca–Mg–Al–Fe fluoride (e.g. ralstonite) and native sulfur. The high temperature deposits show trace element typical of volcanic gas with high enrichment in Re (24 to 79ppb), almost two order of magnitude higher than the corresponding lavas but with Os abundances similar to those of the lavas (14–132 ppt). In contrast the Os contents of the low temperature fluoride deposits (13–77ppb) are higher than any of the other condensates. The fluorides are also enriched in Re, albeit to lesser extent than Os (2.9–15.3ppb). Based on high-temperature samples, the fluid/melt partition coefficients estimated for Re and Os are 100±80 and 1±2, respectively. Considering 1% of fluid loss, these partition coefficients translate into emanation coefficients of 0.50 (0.17–0.65) for Re and 0.01 (0–0.03) for Os. These results indicate that Re, unlike Os, is highly volatile at Piton de la Fournaise.Osmium isotopic compositions of samples collected at medium and low temperature (<350°C) are very uniform and unfractionated (187Os/188Os between 0.130–0.135) and plot within the range of the April 2007 lava flow and the historical lavas of Piton de la Fournaise (i.e. 0.130–0.137). However the highest temperature condensates (Na–K sulfates with T of 384–400°C) yield lower 187Os/188Os ratios (i.e. 0.124–0.129) within the field of mantle signal. Such unradiogenic compositions are best explained if old mantle sulfides occur in lavas and contribute to volcanic gases. Within the general frame of osmium mantle geochemistry, loss of unradiogenic Os during magmas degassing could help to explain osmium isotope disequilibrium between lavas and melting residues.