Seasonal indoor radon concentration in FYR of Macedonia

This paper presents the results of the seasonal indoor radon concentration measurements in dwellings in all regions of the Former Yugoslav Republic (FYR) of Macedonia. The measurements were made in 437 dwellings using CR-39 track detectors over four successive three-month periods (winter, spring, summer and autumn) throughout 2009. The results of analysis of variance showed statistically significant differences between indoor radon concentrations in different seasons. The geometric mean values and geometric standard deviations of indoor radon concentrations in winter, spring, summer and autumn were obtained to be: 115 Bq m^?3 (2.02), 72 Bq m^?3 (1.97), 46 Bq m^?3 (1.95), 92 Bq m^?3 (2.02), respectively. The geometric mean values of spring, summer and autumn to winter ratios were found to be: 0.63 (1.50), 0.40 (1.81), and 0.80 (1.58), respectively. The results of the analysis of the variance showed statistically significant differences among the indoor radon measurements for the regions in different seasons. The influence of the factors linked to building characteristics in relation to radon measurements in different seasons was examined. The factors which enable a differentiation into subgroups (significance level p < 0.05) are the floor level, basement and building materials.     

Estimation of effective doses to cavers based on radon measurements carried out in seven caves of the Bakony Mountains in Hungary

Nowadays, as the practice of extreme sports is spreading, potholing is becoming more and more popular. As a result, both the number of cavers and the time spent in the caves have been on the rise. There are some cavers known to have spent some 5000 h in caves over a span of 10 years. In poorly ventilated caves, radon exhalated from cave rocks and deposits may accumulate and cause significant doses to cavers.In this study, the radon concentration in seven caves in the Bakony Mountains, Hungary, was measured by continuous and integrated measurement devices. Measured values for the different caves were rather different, and varied between 50 and 24,000 Bq m^?3. The average radon concentration over the measurement period was approximately 10,000 Bq m^?3 in five of the seven caves inspected.By assuming an average of 470 h year^?1 spent in caves, effective doses to cavers were estimated. The expected annual effective dose, in case of an equilibrium factor of 0.6, was 19.7 mSv.     

The concentrations and exposure doses of radon and thoron in residences of the rural areas of Kosovo and Metohija

This paper deals with the results of indoor radon and thoron concentrations and exposure doses obtained for 63 dwellings out of the 14 rural communities of Central Kosovo, North Kosovo and Prizren region. These research activities are part of overall radiological research that has systematically been carried out since 1986, particularly in Kosovo and Metohija regions. Passive radon/thoron discriminative detectors, exposed for three months, were used. The arithmetic mean concentrations of indoor radon and thoron are C_Rn = 429 Bq m^?3 C_Tn = 85 Bq m^?3.     

Radon concentrations in schools of the Neapolitan area

A radon survey was carried out in 30 schools located in the metropolitan area around Naples, Italy. Radon concentration was measured using the SSNTD (Solid State Nuclear Track Detectors) method with LR115 detectors. Time integrated measurements covered two consecutive 6-month periods at different locations inside the school buildings: classrooms, laboratories and offices. Data distribution is well fitted by a log-normal curve. The arithmetic mean annual radon concentration is 144 Bq m⁻³, the geometric mean is 86 Bq m⁻³; the standard deviations are respectively 7 Bq m⁻³ and 3. The fractions of rooms where radon concentrations exceed the reference levels of 200, 400 and 500 Bq m⁻³ are 21.3%, 7.6% and 4.5% respectively.The results show that radon concentration in scientific laboratories and in offices is higher than in classrooms.     

Natural radioactivity and human exposure by raw materials and end product from cement industry used as building materials

During the manufacturing process in the cement industry, raw materials of different levels of natural radioactivity are utilized. In this study we present the radiological impact of cements as a building material and the different raw materials used in their manufacture. A total of 218 samples of raw materials and their end product cements were collected from the cement industry of Macedonia (The Former Yugoslav Republic) during the period 2005–2007. The specific activities, evaluated by gamma spectrometry analysis, showed the highest mean specific activity in fly ash (²²⁶Ra, 107 ± 45 Bq kg^?1; ²³²Th, 109 ± 30 Bq kg^?1; ⁴⁰K, 685 ± 171 Bq kg^?1), which is used as a raw material. However, the final cement product usually has relatively lower activity compared with the activity of the raw material and the mean specific activity of the final cement products were lower (²²⁶Ra, 42 ± 10 Bq kg^?1; ²³²Th, 28 ± 6 Bq kg^?1; ⁴⁰K, 264 ± 50 Bq kg^?1). The radium equivalent activity and the hazard index were calculated for each sample to assess the radiation hazard. The mean annual effective dose originating from the cements was found to be 111 ± 22 μSv y^?1, which is below the recommended EC limit of 300 μSv y^?1.     

Systematic grid-wise radon concentration measurements and first radon map in Cyprus

A systematic study of the indoor airborne radon concentration in the central part of the Nicosia district was conducted, using high-sensitivity active radon portable detectors of the type “RADIM3A”. From a total of 108 measurements in 54 grids of 1 km² area each, the overall mean value is 20.6 ± 13.2 Bq m^?3 (A.M. ± S.D.). That is almost twice less than the corresponding average worldwide value. The radon concentration levels in drinking water were also measured in 24 sites of the residential district, using the high-sensitivity radon detector of the type “RADIM3W”. The mean value obtained from these measurements is 243.8 ± 224.8 mBq l^?1, which is relatively low compared to the corresponding internationally accepted level. The associated annual effective dose rates to each measurement were also calculated and compared to the corresponding worldwide values. From the geographical coordinates of the measuring sites and the corresponding radon concentration values, the digital radon map of the central part of the Nicosia district was constructed for the first time, by means of the ArcMap software package.     

Difficulties in the dose estimate of workers originated from radon and radon progeny in a manganese mine

The regulation of radon concentration at workplaces has gained an accentuated importance in all countries. Nevertheless, at this time there is no globally accepted workplace protocol that sets out safe radon concentration values.In this study the radon concentration measured during the working hours and the equilibrium factor, which are necessary for the exact estimation of the radiation dose originating from radon and effecting manganese miners are determined in a Hungarian manganese mine. In order to determine the exact committed effective dose, workers wore track-etched radon.The annual average radon concentration measured at the different points in the mine that was investigated may vary by ±30% relative to the average of the total of the measurement points. The influence of the measurement period is even more significant as the difference related to the annual average may be ±30% with a measurement period of 6 months. The radon concentration level measured during working hours was approximately half of the average measured during the whole period. The measured equilibrium factor was 50% greater than the value given in literature. Disregarding any of these factors may lead to significant errors for the estimation of dose to workers.The average value of the estimated effective radiation dose was 3.7 mSv year⁻¹ based on the personal radon dosimeters.     

Analysis and risk estimates to workers of Brazilian granitic industries and sandblasters exposed to respirable crystalline silica and natural radionuclides

Occupational exposure to respirable crystalline silica and to radiation emitted by natural radionuclides present both in rocks and sands was studied in the Brazilian extractive process and granite product manufacture. Respirable airborne dust samples were collected in working environments, where workers perform different tasks with distinct commercial granites types, and also in places where sandblasters work with sands from different origins. The free crystalline silica contents were determined using X-ray diffraction of the respirable particulate fraction of each sample. Dust samples from granite cutting and sandblasting ambient had the natural radionuclides concentrations measured by gamma spectrometry. Dust concentrations in the workplaces were quite variable, reaching values up to 10 times higher than the respirable particle mass threshold limit value (TLV) set by the American Conference for Governmental Industrial Hygienists of 3 mg m^?3. Also the free crystalline silica concentrations were high, reaching values up to 48 times the TLV of 0.025 mg m^?3. Additionally, our results suggest that the risk of radiation-induced cancer in the granite or marble industries is negligible. However, the combined exposure to dust, gamma radiation, and radon daughter products could result in the enhancement of lung cancer risks associated to sandblasting activities.     

Radiological impacts of natural radioactivity from phosphogypsum piles in Huelva (Spain)

The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K have been measured by gamma spectroscopy in samples of soil collected from the different zones of around Huelva (Spain). The average activity concentrations of ²²⁶Ra (Bq kg^?1) in the active phosphogypsum (PG) stacks, unrestored and restored zones were 647, 573 and 83 respectively. The corresponding values for ²³²Th and ⁴⁰K (Bq kg^?1) were 8, 10 and 25 and 33, 47 and 225 respectively. As a measure of radiation hazard to the occupational workers and public, the Ra equivalent activities, representative level index and dose rates due to natural radionuclides at 1 m above the ground surface were estimated. The average of absorbed dose rates due to ²²⁶Ra, ²³²Th and ⁴⁰K (nGy/h) from active PG stacks, unrestored and restored zones are 284, 255 and 55.The calculated external γ-radiation average dose (mSv/y) received by the workers of the phosphogypsum piles are estimated to be 0.293, 0.262 and 0.057 which is far below the international agreed dose limit of 20 mSv/y (ICRP-60, 1990) for workers. Also, the radiation dose to a member of the public resulting from the use of PG is negligible compared to the average annual effective dose from natural sources (2.4 mSv/y).     

Measuring radon flux across active faults: Relevance of excavating and possibility of satellite discharges

Searching for gas exhalation around major tectonic contacts raises important methodological issues such as the role of the superficial soil and the possible long distance transport. These effects have been studied on the Xidatan segment of the Kunlun Fault, Qinghai Province, China, using measurement of the radon-222 and carbon dioxide exhalation flux. A significant radon flux, reaching up to 538 ± 33 mBq m^?2 s^?1 was observed in a 2–3 m deep trench excavated across the fault. On the soil surface, the radon flux varied from 7 to 38 mBq m^?2 s^?1, including on the fault trace, with an average value of 14.1 ± 1.0 mBq m^?2 s^?1, similar to the world average. The carbon dioxide flux on the soil surface, with an average value of 12.9 ± 3.3 g m^?2 day^?1, also remained similar to regular background values. It showed no systematic spatial variation up to a distance of 1 km from the fault, and no clear enhancement in the trench. However, a high carbon dioxide flux of 421 ± 130 g m^?2 day^?1 was observed near subvertical fractured phyllite outcrops on a hill located about 3 km north of the fault, at the boundary of the large-scale pull-apart basin associated with the fault. This high carbon dioxide flux was associated with a high radon flux of 607 ± 35 mBq m^?2 s^?1. These preliminary results indicate that, at the fault trace, it can be important to measure gas flux at the bottom of a trench to remove superficial soil layers. In addition, gas discharges need to be investigated also at some distance from the main fault, in zones where morphotectonics features support associated secondary fractures.     

Soil radioactivity levels and radiation hazard assessment in the highlands of northern Jordan

Determination of the natural radioactivity has been carried out, by means of gamma-ray spectrometry system, in surface soil samples collected from various geological formations in urban areas of the northern highlands of Jordan. These highlands, extending from Yarmouk River in the north to Wadi Wala in the south, form the agriculturally important regions of Jordan. Soils of the study region, at which about 70% of the total population of the country are living, mainly originated from limestones that are locally used in construction materials, making the evaluation of environmental radioactivity and estimating the current radiation hazards to the population an interesting issue. The total average concentrations of radionuclides ²²⁶Ra, ²³⁸U, ²³²Th, and ⁴⁰K were 42.5, 49.9, 26.7, and 291.1 Bq kg⁻¹, respectively. Correlations made among these radionuclides prove the existence of secular equilibrium in the investigated soils. The total average absorbed dose rate in the study areas is found to be 51.5 nGy h⁻¹, whereas the annual effective dose equivalent has an average value of 63.2 μSv y⁻¹. The external and internal hazard indices, the radium equivalent activity, and the annual gonadal dose equivalent associated with the investigated soils do not exceed the permissible limits except for soils originated from phosphate rocks. Moreover, the radio-elemental concentrations of uranium, thorium and potassium, evaluated for the various geological features in the study areas were calculated to indicate whether relative depletion/enrichment of radioisotopes had occurred. The results of the present study were discussed and compared with internationally recommended values.     

Lipase catalyzed ultrasonic synthesis of poly-4-hydroxybutyrate-co-6-hydroxyhexanoate

Four different lipases were compared for ultrasound-mediated synthesis of the biodegradable copolymer poly-4-hydroxybutyrate-co-6-hydroxyhexanoate. The copolymerization was carried out in chloroform. Of the enzymes tested, Novozym 435 exhibited the highest copolymerization rate, in fact the reaction rate was observed to increase with about 26-fold from 30 to 50 °C (7.9 × 10^?3 M s^?1), sonic power intensity of 2.6 × 10³ W m^?2 and dissipated energy of 130.4 J ml^?1. Copolymerization rates with the Candida antarctica lipase A, Candida rugosa lipase, and Lecitase Ultra? were lower at 2.4 × 10^?4, 1.3 × 10^?4 and 3.5 × 10^?4 M s^?1, respectively. The catalytic efficiency depended on the enzyme. The efficiency ranged from 4.15 × 10^?3 s^?1 M^?1 for Novozym 435–1.48 × 10^?3 s^?1 M^?1 for C. rugosa lipase. Depending on the enzyme and sonication intensity, the monomer conversion ranged from 8.2% to 48.5%. The sonication power, time and temperature were found to affect the rate of copolymerization. Increasing sonication power intensity from 1.9 × 10³ to 4.5 × 10³ W m^?2 resulted in an increased in acoustic pressure (P_a) from 3.7 × 10⁸ to 5.7 × 10⁸ N m^?2 almost 2.4–3.7 times greater than the acoustic pressure (1.5 × 10⁸ N m^?2) that is required to cause cavitation in water. A corresponding acoustic particle acceleration (a) of 9.6 × 10³–1.5 × 10⁴ m s^?2 was calculated i.e. approximately 984–1500 times greater than under the action of gravity.     

Radon activity measurements around Bakreswar thermal springs

²²²Rn concentrations were measured in the bubble gases, spring waters, soil gases and in ambient air around the thermal springs at Bakreswar in West Bengal, India. This group of springs lies within a geothermal zone having exceptionally high heat flow about 230 mW/m², resembling young oceanic ridges. The spring gas has a high radon activity (～885 kBq/m³) and is rich in helium (～1.4 vol. %) with appreciably large flow rate. The measured radon exhalation rates in the soils of the spring area show extensive variations from 831 to 4550/mBqm² h while ²²²Rn concentrations in the different spring waters vary from 3.18 to 46.9 kBq/m³. Surface air at a radius of 40 m around the springs, within which is situated the Bakreswar temple complex and a group of dwellings, has radon concentration between 450 and 500 Bq/m³. In the present paper we assess the radon activity background in and around the spring area due to the different contributing sources and its possible effect on visiting pilgrims and the people who reside close to the springs.     

Fast directional multilevel summation for oscillatory kernels based on Chebyshev interpolation

Many applications lead to large systems of linear equations with dense matrices. Direct matrix-vector products become prohibitive, since the computational cost increases quadratically with the size of the problem. By exploiting specific kernel properties fast algorithms can be constructed.A directional multilevel algorithm for translation-invariant oscillatory kernels of the type K(x, y) = G(x ? y)e^?k∣x?y∣, with G(x ? y) being any smooth kernel, will be presented. We will first present a general approach to build fast multipole methods (FMMs) based on Chebyshev interpolation and the adaptive cross approximation (ACA) for smooth kernels. The Chebyshev interpolation is used to transfer information up and down the levels of the FMM. The scheme is further accelerated by compressing the information stored at Chebyshev interpolation points using ACA and QR decompositions. This leads to a nearly optimal computational cost with a small pre-processing time due to the low computational cost of ACA. This approach is in particular faster than performing singular value decompositions.This does not address the difficulties associated with the oscillatory nature of K. For that purpose, we consider the following modification of the kernel K^u = K(x, y)e^??ku·(x?y), where u is a unit vector (see Brandt [1]). We proved that the kernel K^u can be interpolated efficiently when x ? y lies in a cone of direction u. This result is used to construct an FMM for the kernel K.Theoretical error bounds will be presented to control the error in the computation as well as the computational cost of the method. The paper ends with the presentation of 2D and 3D numerical convergence studies, and computational cost benchmarks.     

Oxygen-rich Ti1−xO2 pillar growth at a gold nanoparticle–TiO2 contact by O2 exposure

In-situ gas-injection transmission electron microscopy revealed that a pillar grew at the edge of the interface of a gold nanoparticle and a TiO₂ substrate during exposure to O₂ gas at 100 Pa. The pillar was found to have a titanium-deficient chemical composition of Ti_1 ? xO₂ (x > 0) by electron energy loss spectroscopy (EELS). The spectra showed a chemical shift of oxygen and titanium ions to have ionic states of Ti³⁺ and O^y? (y < 3/2). The formation of the Ti_1 ? xO₂ at the contact edge of gold–Ti_1 ? xO₂ interface is discussed from the perspective of an O₂ affinity, which plays an important role in CO oxidation process of supported gold particle.     

Modification of B-site doping of perovskite LaxSr1 − xFe1 − y−zCoyCrzO3 − δ oxide by Mg2+ ion

Co-doping B-site of perovskite oxide La_xSr_1 ? xCo_yFe_1 ? yO_3 ? δ (LSCFO) with Cr⁶⁺ and Mg²⁺ ions has been attempted in this research for revamping chemical stability and oxygen ionic conductivity of this mixed conducting oxide. It is known that partial substitution for B-site cations of LSCFO by Cr gives rise to a significant improvement on chemical and thermal stability of the perovskite oxide. On the basis of this doped structure, introduction of an immaterial dose of Mg²⁺ ion into its B-site results in a microstructure consisting of smaller grains with higher density than its precursor. Furthermore, the resulting perovskite oxide La_0.19Sr_0.8Fe_0.69Co_0.1Cr_0.2 Mg_0.01O_3 ? δ (LSFCCMO) displays higher O^2? conductivity than the solely Cr-doped LSCFO besides the improved chemical stability against reduction in 5% CH₄/He stream at 850 °C. A detailed examination of the oxidation states of B-site transition metal ions by XPS has also been conducted as a part of structural characterizations of LSFCCMO. The assessment of relative O^2? conductivity shows that the grain boundary area plays a more important role than the bulk phase in facilitating ion transport, but with comparable boundary areas the higher densification level is favorable.     

Chloroethene dehalogenation with ultrasonically produced air-stable nano iron

Zerovalent iron (ZVI) has been demonstrated to be suitable for the dehalogenation of environmental pollutants such as chloroethenes. The construction of ZVI reactive barriers by conventional engineering measures is expensive and limited to shallow aquifers. The use of nanosized ZVI particles opens new opportunities to construct ZVI barriers with less invasive techniques. However, nanosized particles of pure ZVI are pyrophoric and react spontaneously with atmospheric oxygen.In this study, nanosized air-stable ZVI particles were produced by applying ultrasound to a solution of Fe(CO)₅ in edible oil. The resulting iron nanoparticles were dispersed in a carbon matrix, and coated with a non-crystalline carbon layer of approx. 2.5 nm. Although, these nanoparticles are non-pyrophoric and stable in air, dechlorination of tetrachloroethene was demonstrated in synthetic aqueous medium and in polluted groundwater. Additionally, hydrogen was formed. Due to the larger surface area, significantly higher mass-normalized reaction rates of the novel carbon-coated nanoparticles were obtained as compared to conventional bulk ZVI material. Surface normalized pseudo-first-order-reaction rates of k_SA = 3.49 × 10^?3 L h^?1 m^?2 and 2.33 × 10^?2 L h^?1 m^?2 were calculated for the nano-ZVI and the bulk ZVI, respectively. Dechlorination reaction products of the novel nano-ZVI were trichloroethene, cis-dichloroethene, vinyl chloride, ethene, and ethane.     

Preparation of enzyme nanoparticles and studying the catalytic activity of the immobilized nanoparticles on polyethylene films

Using high-intensity ultrasound, in situ generated α-amylase nanoparticles (NPs) were immobilized on polyethylene (PE) films. The α-amylase NP-coated PE films have been characterized by E-SEM, FTIR, DLS, XPS and RBS. The PE was reacted with HNO₃ and NPs of the α-amylase were also deposited on the activated PE. The PE impregnated with α-amylase (4 μg per 1 mg PE) was used for hydrolyzing soluble potato starch to maltose. The immobilization improved the catalytic activity of α-amylase at all the reaction conditions studied. The kinetic parameters, K_m (5 and 4 g L^?1 for the regular and activated PE, respectively) and V_max (5 × 10^?7 mol ml^?1 min^?1, almost the same numbers were obtained for the regular and activated PEs) for the immobilized amylase were found to slightly favor the respective values obtained for the free enzyme (K_m = 6.6 g L^?1, V_max = 3.7 × 10^?7 mol ml^?1 min^?1). The enzyme remained bound to PE even after soaking the PE in a starch solution for 72 h and was still found to be weakly active.     

Novel bending sensor based on a meniscus shaped beam with LPG

A novel bending sensor based on a long period fiber grating (LPG) is presented. A LPG was glued into a V-shaped groove, which lies on the lower surface of a meniscus shaped beam. It is found that the transmission optical power of the LPG changed linearly with the variation of the bending of the beam. The bending applied on the beam can be measured by detecting the intensity variation of the LPG's resonant dip wavelength. Under a relative large bending measured range from 0 to 7.5 m^?1, the sensitivity of 3.003 dB m^?1 and curvature resolution of 0.001 m^?1 have been achieved for the proposed bending sensor.     

A ceria layer as diffusion barrier between LAMOX and lanthanum strontium cobalt ferrite along with the impedance analysis

A thin interlayer of samarium doped ceria (SDC) is applied as diffusion barrier between La_1 ? xSr_xCo_yFe_1 ? yO₃ x = 0.1–0.4, y = 0.2–0.8 (LSCF) cathode and La_1.8Dy_0.2Mo_1.6W_0.4O₉ (LDMW82) electrolyte to obstruct Mo–Sr diffusion and solid state reaction in the intermediate temperature range of SOFC. We demonstrate the effectiveness of the diffusion barrier through contrasting the clearly defined interfaces of LSCF/SDC/LDMW82 against a rugged growing product layer of LSCF/LDMW82 in 800 °C thermal annealing, and analyze the product composition and the probable new phase. In addition, the measured polarization resistance is considerably lower for the half-cell with a diffusion barrier. Therefore, the electrochemical performance of the LSCF cathode is investigated on the SDC-protected LDMW82. The cell with LSCF (x = 0.4) persistently outperforms the one with x = 0.2 in polarization resistance because of its small low-frequency contribution. The activation energy of polarization resistance is also lower for La_0.6Sr_0.4Co_yFe_1 ? yO₃ (112–135 kJ/mol), than that for La_0.8Sr_0.2Co_yFe_1 ? yO₃ (156–164 kJ/mol). La_0.6Sr_0.4Co_yFe_1 ? yO₃ y = 0.4–0.8 is the proper composition for the cathode interfaced to SDC/LDMW82.