222Rn Emanation Coefficient Research Articles

EMANATION OF RADON-222 FROM DIFFERENT SOIL TYPES AND SOIL GROUPS

In this paper, we deal with measurement of 222Rn emanation coefficient (Ke) of soils using an accumulation method. We created a database of Ke values of dried soils for various soil types and soil groups, classified by the size of soil particles. For 18 different soil samples we obtained the Ke values in range 0.083-0.234. The analysis of radon emanation dependence on moisture for seven of these samples shows two different trends which were related to soil texture (clays or sands). Soils with predominant sandy particles prove weak dependence on moisture and Ke values from minimum value (at zero moisture) do not increase much (max 15% increase on every 5% of moisture), for soils with majority of clayey particles the moisture can affect the Ke more significantly (increase up to 60%).

Ion implantation of 226Ra for a primary 222Rn emanation standard

Laser resonance ionization at the RISIKO 30 kV mass separator has been used to produce isotopically and isobarically pure and well quantified 222Rn emanation standards. Based upon laser-spectroscopic preparation studies, ion implantation into aluminum and tungsten targets has been carried out, providing overall implantation efficiencies of 40% up to 60%. The absolute implanted activity of 226Ra was determined by the technique of defined solid-angle α-particle spectrometry, where excellent energy resolution was observed. The 222Rn emanation coefficient of the produced targets was studied using α-particle and γ-ray spectrometry, and yielded results between 0.23 and 0.34, with relative uncertainty on the order of 1%. No dependence exceeding a 1% change of the emanation on humidity could be identified in the range of 15 %rH to 75 %rH, whereas there were hints of a slight correlation between the emanation and temperature. Additionally, and as expected, the emanation coefficient was found to be dependent on the target material as well as the implanted dose.

Study on radon (222Rn) emanation coefficient and mass exhalation rate from heavy minerals of high specific gravity

A study on 222Rn emanation coefficient and mass exhalation rate was carried out for different minerals having high specific gravity collected from a natural high background radiation area of India. The mass exhalation rate varied from 31 ± 0.5 to 2366 ± 36 mBq kg−1 h−1 and the radon emanation coefficient varied from 1.02 × 10−2 to 2.04 × 10−1. The radon escape probability was highest in garnet mineral indicating the uniform distribution of radium atoms on the mineral surface and smaller grain size than other minerals. Statistical analysis revealed that the radon mass exhalation rate was positively correlated with the 226Ra activity whereas no such strong significant correlation was observed between radon emanation coefficient and 226Ra activity.

The first radon potential map of the Campania region (southern Italy)

This is the first paper to report a potential map of radon (222Rn) distribution in the Campania region of southern Italy, using the geostatistical kriging interpolation method using QGIS® software. The response variable is the 222Rn indoor measurements, whereas proxy variables used as predictors are: geology, faults, soils permeability, meteorological/climatic parameters, 238U distribution, 222Rn emanation coefficients and exhalation rates, 226Ra in building materials and gamma dose rate in dwellings. The map shows high radon potential areas in correspondence to the main volcanic centres and the faults network of the region. The map is a useful instrument to identify radon-prone areas and evaluate radon risk level for the population.

Natural Radioactivity of the Crystalline Basement Rocks of the Peloritani Mountains (North-Eastern Sicily, Italy): Measurements and Radiological Hazard.

Crystalline rocks can produce dangerous radiation levels on the basis of their content in radioisotopes. Here, we report radiological data from 10 metamorphic and igneous rock samples collected from the crystalline basement of the Peloritani Mountains (southern Italy). In order to evaluate the radiological properties of these rocks, the gamma radiation and the radon emanation have been measured. Moreover, since some of these rocks are employed as building materials, we assess the potential hazard for population connected to their use. Gamma spectroscopy was used to measure the 226Ra, 232Th and 40K activity concentration, whereas the radon emanation was investigated by using a RAD 7 detector. The results show 226Ra, 232Th and 40K activity concentration values ranging from (17±4) to (56±8) Bq kg-1, (14±3) to (77±14) Bq kg-1 and (167±84) to (1760±242) Bq kg-1, respectively. Values of the annual effective dose equivalent outdoor range from 0.035 to 0.152mSv y-1, whereas the gamma index is in the range of 0.22-0.98. The 222Rn emanation coefficient and the 222Rn surface exhalation rate vary from (0.63±0.3) to (8.27±1.6)% and from (0.12±0.03) to (2.75±0.17) Bq m-2h-1, respectively. The indoor radon derived from the building use of these rocks induces an approximate contribution to the annual effective dose ranging from 8 to 176μSv y-1. All the obtained results suggest that the crystalline rocks from the Peloritani Mountains are not harmful for the residential population, even though they induce annual effective doses due to terrestrial gamma radiation above the worldwide average values. Moreover, their use as building materials does not produce significant health hazards connected to the indoor radon exposure.

222Rn and 220Rn emanations from powdered samples of samarskite as a function of annealing temperature

Abstract Emanation coefficients for radon (222Rn) and thoron (220Rn) were measured from fully metamict samarskite collected from Centennial Cone after 1 h and 24 h annealing in argon from 473 to 1373 K. For the 1 h annealing run, 222Rn emanation coefficients ranged from 5 × 10-6 to 2.1 × 10-5 %, while 220Rn coefficients varied from 6.3 × 10-3 to 2 × 10-2 %. For the 24 h annealing run, 222Rn coefficients ranged from 5.8 × 10-6 to 2.3 × 10-5 %, while 220Rn coefficients varied from 4.1 × 10-3 to 1.5 × 10-2 %. The 222Rn and 220Rn emanation coefficients vs. annealing temperature data can be described by an exponentially decreasing sinusoidal function. Both 222Rn and 220Rn emanation coefficient values after annealing considerably exceeded those measured from an unheated powder reference sample and from the original samarskite sample.

Measurements of radon (222Rn) and thoron (220Rn) exhalations and their decay product concentrations at Indian Stations in Antarctica

During the 33rd summer expedition to the two Indian Stations at Antarctica, Bharati and Maitri, radon and thoron progeny concentrations in indoors and outdoors were measured along with radon (222Rn)/thoron (220Rn) exhalation rate measurements of soil samples, radionuclide content and 222Rn emanation coefficient. This investigation was based on the reports of the higher gamma radiation levels reported around these stations. The results will give an estimate of the radioactivity level as well as the total dose received by personnel carrying out long-term measurements at these stations. Radon and thoron progeny concentrations were measured using direct radon and thoron progeny sensors (DRPS and DTPS). The soil radionuclide content was measured using HPGe gamma spectrometry while radon/thoron exhalation rates were measured using the accumulation method by scintillation radon/thoron monitor. In contrast to a higher radiation field and radioactivity content, studies showed the radon/thoron exhalation rates and progeny concentration to be similar to that measured in normal background areas of other parts of the world. This could be attributed to the ice deposits and the larger atmospheric dispersion, and also to the soil nature which is mainly loamy sands with low clay content contributing to a lower emanation. The results are discussed.

222Rn and220Rn emanations as a function of the absorbed α-doses from select metamict minerals

Metamict minerals contain uranium and thorium, which contribute to physical degradation or metamictization of their crystal structures over geologic time. The damage occurs primarily through progressive overlapping recoil nuclei collision cascades from α-decay of 238U, 232Th, 235U, and their daughter products. We measured 222Rn and 220Rn emanations from metamict samples of nine oxides (brannerite, davidite, fergusonites, pyrochlores, samarskites, and uraninite), two phosphates (monazites), and eight silicates (cerite, gadolinites, perrierite, rinkite, thorite, turkestanite, and vesuvianite). The total absorbed α-doses ranged from 1.4 × 1015 to 6.1 × 1018 α-decay mg−1 for cerite and uraninite, respectively. The 222Rn emanation coefficients varied from 5 × 10−5% (uraninite) to 2.5% (turkestanite). The 220Rn emanation coefficients varied from 7 × 10−3% (gadolinite Ytterby) to 6.2% (gadolinite Marysin). The lowest 222Rn emanation coefficients occurred among metamict minerals containing the highest concentrations of 238U (i.e., uraninite, samarskites, and brannerite). Overall, the 222Rn and 220Rn emanation coefficients observed in this study fall significantly below previously reported values.

Assessment of inhalation exposure potential of broken uranium ore piles in low-grade uranium mine

This paper presents the assessment of inhalation exposure potential of broken uranium ore piles in different stopes of Jaduguda uranium mines of India. 222Rn emanation coefficient of broken uranium ore was measured in laboratory by collecting air sample from airtight glass jar containing ore sample. An attempt was also made to correlate the emanation coefficient with 226Ra content of the ore. The 222Rn progeny doses estimated based on radon activity concentration of broken ore, occupancy period and equilibrium ratio in different stopes were well below the prescribed limit of International Commission on Radiological Protection. The maximum 222Rn progeny dose contribution from broken ore piles was worked out to be 0.22 mSv year−1. This suggests that the broken ore piles are not the significant contributor of inhalation exposure under the existing ventilation condition of Jaduguda uranium mine.

Radon exhalation rates and gamma doses from ceramic tiles.

This study was carried out to assess the possible radiological hazard resulting from the use of zircon in glaze applied to tiles used in buildings. The 226Ra content of various stains and glazing compounds was measured using gamma spectroscopy and the 222Rn exhalation rates for these materials were measured using adsorption on activated charcoal. The radon exhalation rates were found to be close to or less than the minimum detectable values for the equipment used. This limit was much lower than the estimated exhalation rates, which were calculated assuming that the parameters controlling the emanation and diffusion of 222Rn in the materials studied were similar to those of soil. This implied that the 222Rn emanation coefficients and/or diffusion coefficients for most of the materials studied were very much lower than expected. Measurements on zircon powders showed that the 222Rn emanation coefficient for zircon was much lower than that for soil, indicating that only a small fraction of the 222Rn produced by the decay of 226Ra was able to escape from the zircon grains. The estimated increase in radon concentration in room air and the estimated external gamma radiation dose resulting from the use of zircon glaze are both much lower than the relevant action level and dose limit.

Radon emanation coefficients for phosphogypsum.

Phosphogypsum is a by-product of the phosphate fertilizer industry which is stockpiled in large quantities world-wide. Phosphogypsum consists mainly of dihydrate gypsum (CaSO42H2O) but also contains elevated concentrations of 226Ra and other inorganic species which originate from the processing of phosphate rock. 222Rn gas is the first decay product of 226Ra and has been identified as one of the major environmental concerns associated with phosphogypsum. This study was conducted to determine effects of particle size, weathering, and moisture content on the 222Rn emanation coefficient (epsilon) for phosphogypsum. Average epsilon for air-dry, unfractionated phosphogypsums derived from Togo, Florida, or Idaho rock was approximately 12%. Average epsilon for fine fraction phosphogypsum (< 20 microns diameter) was greater than for unfractionated phosphogypsum by a factor of 4.6, 1.4, and 4.4 for samples derived from Idaho rock, Togo rock, and Florida rock, respectively. Phosphogypsum samples subjected to an artificial weathering procedure lost 40% mass, with no change in epsilon. Increasing water content was found to first slightly decrease, then to increase epsilon compared to air-dry samples; epsilon for 100% saturated phosphogypsum was 1.9-fold greater than in air-dry phosphogypsum. Particle size sorting could account for variability of 222Rn exhalation at repositories. Very high moisture contents could slightly increase 222Rn emanation, but exhalation would likely be reduced due to slow diffusion through porosity of saturated phosphogypsum.

Investigations of a specific surface area of a material on the basis of 222Rn emanation coefficient measurements.

A theoretical model of Rn emanation by a crystal lattice into the pore space of a material is presented. This model makes it possible to calculate the pore emanation rate of a material. Measurements of the 222Rn emanation coefficient of lightweight concrete for different grain sizes were performed. Using the results of the measurements and the calculated value of a pore emanation rate, a specific surface area of the material was determined. For non-ground lightweight concrete, this value is (1.40 +/- 0.13) x 10(4) cm2 g-1. It is shown that grinding to grain sizes below 60 microns is required to cause a significant increase of specific surface area and thus of the emanation coefficient. However, these results should be treated only as an estimation because the analysis does not account for the real structure of the lightweight concrete. The aim of this work is to present the possibility of connecting the theoretical calculations with the results of measurements in order to determine the specific surface area of a material.

Theoretical evaluation of the 222Rn emanation coefficient for coal fly ash.

The release of 222Rn, from individual material grains in which it is formed, may be largely a diffusion process. This paper presents an analytical model purporting to describe the physical process of the release of 222Rn atoms from a 226Ra-bearing material grain. The solution of the diffusion equation for a spherical grain permits us to calculate theoretically the diffusion and emanation coefficient. Using this analysis to interpret experimental release data is explained.

Radium-226 contents and Rn emanation coefficients of particle-size fractions of alkaline, acid and mixed U mill tailings.

Alkaline circuit and mixed, acid and alkaline circuit U mill tailings sampled at an inactive mill site near Monticello, UT, and tailings from an active, acid-leach U mill were separated into particle-size fractions ranging from +10 mesh to -325 mesh by dry and wet separation techniques. The 226Ra contents and 222Rn emanation coefficients of these fractions were determined. Dry tailings show a high degree of aggregation that tends to mask the relation of properties, such as Ra content and Rn emanating power, to dispersed-particle size. Coarse-tailings fractions (+325 mesh) had emanation coefficients which were from 25 to 45% lower than those of their fine-fraction counterparts. Emanation coefficients measured for tailings derived from a salt roast/carbonate-leach process suggest that such are roasting does not lead to reductions in Rn emanation in the tailings derived therefrom.

The effects of particle size and moisture content on the emanation of Rn from coal ash.

Measurements of the emanation coefficients of 222Rn from coal ash were performed. Samples of coal ash from a stoker-fired furnace were mechanically sized into four categories. The mean 226Ra concentration of these categories ranged from 11.82-16.77 dpm g-1 and increased as a function of decreasing particle size. The mean bulk density and mean specific gravity of these categories ranged from 0.488-0.944 g cm-3 and 2.017-2.390 g cm-3, respectively, and both increased as a function of decreasing particle size. Samples of coal ash from four pulverized coal-fired furnaces were obtained, and demonstrated mean 226Ra concentrations ranging from 6.44-7.59 dpm g-1. The mean bulk density and mean specific gravity of these samples ranged from 1.254-1.520 g cm-3 and 2.357-2.588 g cm-3, respectively. Construction of chambers and methods for measuring 222Rn emanation coefficients are described. The measured emanation coefficient is shown to be insensitive to ingrowth time at times greater than three days. Measurements of emanation coefficients from ash samples were conducted at moisture contents of 0, 1.0, 10, 20 and 40% moisture by weight, and showed an increase in the emanation coefficient as a function of moisture content up to about 20% moisture by weight. Above 20% moisture content, most samples showed a trend toward decreasing emanation coefficients. The fractionated ash samples showed an increase in the emanation coefficient as a function of decreasing particle size. An experiment was also conducted which confirmed that sample depth was insignificant in explaining the observed emanation coefficient over the range of depths used in the other experiments.