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.     

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.     

Exposure to indoor radon and natural gamma radiation in public workplaces in north-western Greece

Measurements of indoor radon levels and gamma dose rates were performed in 42 workplaces in Ioannina, north-western Greece. Radon concentrations followed a log-normal distribution with an arithmetic mean of 95 ± 51 Bq m^?3. In all cases, radon levels were below 400 Bq m^?3, which is the action level implemented by the Greek Regulation for Radiation Protection, in accordance with the European Commission recommendation. Comparing summer and winter measurements, no statistically significant seasonal variation was established. However, radon concentrations measured in basement and ground floor workplaces were significantly higher (p < 0.01) than those measured in the first and upper floors. Annual effective dose rates from inhalation of radon and its decay products were estimated to be in the range from 0.13 to 1.36 mSv y^?1 with a mean value of 0.62 mSv y^?1. Indoor exposure to natural gamma radiation entailed an average effective dose rate of 0.13 mSv y^?1, of which approximately 62% was due to terrestrial and the rest due to cosmic sources. The reported data contribute to the assessment of radon distribution and dose estimate at the national level.     

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.     

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.     

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.     

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.     

Fiber curvature sensor based on spherical-shape structures and long-period grating

A novel curvature sensor based on optical fiber Mach–Zehnder interferometer (MZI) is demonstrated. It consists of two spherical-shape structures and a long-period grating (LPG) in between. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivity are −22.144 nm/m⁻¹ in the measurement range of 5.33–6.93 m⁻¹, −28.225 nm/m⁻¹ in the range of 6.93–8.43 m⁻ and −15.68 nm/m⁻¹ in the range of 8.43–9.43 m⁻¹, respectively. And the maximum curvature error caused by temperature is only −0.003 m⁻¹/°C. The sensor exhibits the advantages of all-fiber structure, high mechanical strength, high curvature sensitivity and large measurement scales.     

Electrically forced microthreading of highly viscous dielectric liquids

The behaviour of three high viscosity (4875, 12 125 and 58 560 mPa s), dielectric liquids was investigated at flow rates of 10⁻¹⁰, 10⁻¹² and 10⁻¹⁴ m³ s⁻¹ and the applied voltage range 6–15 kV. In these experiments, due to the low electrical conductivity of the liquids (10⁻¹³ S m⁻¹) and therefore the ensuing high electrical relaxation time, classical electrohydrodynamic atomization conditions are not satisfied. Only dripping and unstable jetting were observed at 4875 mPa s. A transition from no jetting to stable microthreading was observed for the 12 125 and 58 560 mPa s samples. The relics accompanying the transition were found to change from discrete droplets to a continuous filament. Stable microthreading, which generates uniform filaments, was obtained for the 12 125 mPa s sample at flow rates 10⁻¹⁰ and 10⁻¹² m³ s⁻¹ and in the case of the 58 560 mPa s sample at all the flow rates investigated. The high viscosity assisted stable microthreading with the filament diameter decreasing with increasing applied voltage and more dramatically decreasing with reducing flow rate.     

A Boubaker polynomials expansion scheme (BPES)-related protocol for measuring sprayed thin films thermal characteristics

Measurements of In₂S₃ and ZnIn₂S₄ sprayed thin films thermal characteristics have been carried out using the photodetection technique. The thermal conductivity k and diffusivity D were obtained using a new protocol based on photothermal signal parameters analysis. Measured values of k and D were respectively, (15.2 ± 0.85) W m⁻¹K⁻¹ and (69.8 ± 7.1) × 10⁻⁶ m²s⁻¹ for In₂S₃, (7.2 ± 0.7) W m⁻¹K⁻¹ and (32.7 ± 4.3) × 10⁻⁶ m²s⁻¹ for ZnIn₂S₄. These values are extremely important since similar compounds are more and more proposed as Cd-free alternative materials for solar cells buffer layers.     

Anomalous strain effect on the thermal conductivity of borophene: a reactive molecular dynamics study

Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, has been recently synthesized. Here we investigate mechanical properties and lattice thermal conductivity of borophene using reactive molecular dynamics simulations. We performed uniaxial tensile strain simulations at room temperature along in-plane directions, and found 2D elastic moduli of 188 N m⁻¹ and 403 N m⁻¹ along zigzag and armchair directions, respectively. This anisotropy is attributed to the buckling of the borophene structure along the zigzag direction. We also performed non-equilibrium molecular dynamics to calculate the lattice thermal conductivity. Considering its size-dependence, we predict room-temperature lattice thermal conductivities of 75.9 ± 5.0 W m⁻¹ K⁻¹ and 147 ± 7.3 W m⁻¹ K⁻¹, respectively, and estimate effective phonon mean free paths of 16.7 ± 1.7 nm and 21.4 ± 1.0 nm for the zigzag and armchair directions. In this case, the anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. We also observe that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. For a strain of 8% along the armchair direction the thermal conductivity increases by a factor of 3.5 (250%), whereas for the same amount of strain along the zigzag direction the increase is only by a factor of 1.2 (20%). Our predictions are in agreement with recent first principles results, at a fraction of the computational cost. The simulations shall serve as a guide for experiments concerning mechanical and thermal properties of borophene and related 2D materials.     

First principles study of the structure,electronic state and stability of AlnAsm− anions

Structural and electronic properties of semiconductor binary microclusters Al_nAs_m⁻ anions have been investigated using the B3LYP-DFT method in the ranges of n = 1,2 and m = 1–7. Full structural optimization, adiabatic electron affinities calculation and frequency analysis are performed with the basis of 6–311 + G(d). The charged-induced structural changes in these anions have been discussed. The strong As–As bond is also favored over Al–As bonds in the Al_nAs_m⁻ anions in comparison with corresponding neutral cluster. Among different AlAs_m⁻ and Al₂As_m⁻ (m = 1–7) anions, AlAs₄⁻ and Al₂As₃⁻ are most stable.     

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.     

Electrical and optical characteristics of a Si-doped (Al)GaInAs digital alloy/AlInAs-distributed Bragg mirrors on InP

We report electrical and optical characteristics of a Si-doped (Al)GaInAs digital alloy/AlInAs Bragg mirror lattice matched to InP grown by molecular beam epitaxy. A 98.2% reflectivity with a 107 nm stop band width centred at 1.54 μ m is obtained. An average voltage drop of 16 mV per period at a current density of 1 KA cm ^− 2is observed for a mean electron concentration of about 5.5  ×  10¹⁸cm ^− 3. The influence of structural and intrinsic properties of the heterostructure on the electrical resistivity and optical reflectivity is analysed.     

Ionic conductivity of polymer electrolyte membranes based on polyphosphazene with oligo(propylene oxide) side chains

A polyphosphazene [NP(NHR)₂]_n with oligo[propylene oxide] side chains − R = –[CH(CH₃)–CH₂O]_m–CH₃ (m = 6 – 10) was synthesized by living cationic polymerisation and polymer-analogue substitution of chlorine from the intermediate precursor [NPCl₂]_n using the corresponding primary amine RNH₂. The polymer had an average molecular weight of 3.3 × 10⁵ D. Polymer electrolytes with different concentrations of dissolved lithium triflate (LiCF₃SO₃) were prepared. Mechanically stable polymer electrolyte membranes were formed using UV radiation induced crosslinking of the polymer salt mixture in the presence of benzophenone as photoinitiator. The glass transition temperature of the parent polymer was found to be − 75 °C before cross linking. It increases after crosslinking and with increasing amounts of salt to a maximum of − 55 °C for 20 wt.% LiCF₃SO₃. The ionic conductivity was determined by impedance spectroscopy in the temperature range 0–80 °C. The highest conductivity was found for a salt concentration of 20 wt.% LiCF₃SO₃: 6.5 × 10^− 6 S·cm^− 1 at 20 °C and 2.8 × 10^− 4 S cm^− 1 at 80 °C. The temperature dependence of the conductivities was well described by the MIGRATION concept.     

A new way to apply ultrasound in cross-flow ultrafiltration: Application to colloidal suspensions

A new coupling of ultrasound device with membrane process has been developed in order to enhance cross-flow ultrafiltration of colloidal suspensions usually involved in several industrial applications included bio and agro industries, water and sludge treatment. In order to reduce mass transfer resistances induced by fouling and concentration polarization, which both are main limitations in membrane separation process continuous ultrasound is applied with the help of a vibrating blade (20 kHz) located in the feed channel all over the membrane surface (8 mm between membrane surface and the blade). Hydrodynamic aspects were also taking into account by the control of the rectangular geometry of the feed channel.Three colloidal suspensions with different kinds of colloidal interaction (attractive, repulsive) were chosen to evaluate the effect of their physico-chemical properties on the filtration.For a 90 W power (20.5 W cm⁻²) and a continuous flow rate, permeation fluxes are increased for each studied colloidal suspension, without damaging the membrane. The results show that the flux increase depends on the initial structural properties of filtered dispersion in terms of colloidal interaction and spatial organizations.For instance, a Montmorillonite Wyoming–Na clay suspension was filtered at 1.5 × 10⁵ Pa transmembrane pressure. Its permeation flux is increased by a factor 7.1, from 13.6 L m⁻² h⁻¹ without ultrasound to 97 L m⁻² h⁻¹ with ultrasound.     

Preparation and electrochemical properties of mesoporous Co3O4 crater-like microspheres as supercapacitor electrode materials

Mesoporous Co₃O₄ microspheres with unique crater-like morphology were obtained by utilizing the mesoporous silica material MCM-41 as a template. The analysis results of N₂ adsorption–desorption measurement indicate that the product has a large Brunauer–Emmett–Teller (BET) surface area of 60 m² g⁻¹ and a narrow pore size distribution centering around 3.7 nm. Its electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The findings reveal that this novel morphology material has a smaller inner resistance of about 0.4 Ω and a higher onset frequency of 550 Hz. This material can provide a high specific capacitance of 102 F g⁻¹ and a large capacity retention of 74% in 500 continuous cycles test at a sweep rate of 3 mV s⁻¹. More significantly, the mass loading of electroactive species can reach as large as 2 mg cm⁻², which is one order of magnitude larger than common amount used.     

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.     

Rapid preparation of high electrochemical performance LiFePO4/C composite cathode material with an ultrasonic-intensified micro-impinging jetting reactor

A joint chemical reactor system referred to as an ultrasonic-intensified micro-impinging jetting reactor (UIJR), which possesses the feature of fast micro-mixing, was proposed and has been employed for rapid preparation of FePO₄ particles that are amalgamated by nanoscale primary crystals. As one of the important precursors for the fabrication of lithium iron phosphate cathode, the properties of FePO₄ nano particles significantly affect the performance of the lithium iron phosphate cathode. Thus, the effects of joint use of impinging stream and ultrasonic irradiation on the formation of mesoporous structure of FePO₄ nano precursor particles and the electrochemical properties of amalgamated LiFePO₄/C have been investigated. Additionally, the effects of the reactant concentration (C = 0.5, 1.0 and 1.5 mol L⁻¹), and volumetric flow rate (V = 17.15, 51.44, and 85.74 mL min⁻¹) on synthesis of FePO₄·2H₂O nucleus have been studied when the impinging jetting reactor (IJR) and UIJR are to operate in nonsubmerged mode. It was affirmed from the experiments that the FePO₄ nano precursor particles prepared using UIJR have well-formed mesoporous structures with the primary crystal size of 44.6 nm, an average pore size of 15.2 nm, and a specific surface area of 134.54 m² g⁻¹ when the reactant concentration and volumetric flow rate are 1.0 mol L⁻¹ and 85.74 mL min⁻¹ respectively. The amalgamated LiFePO₄/C composites can deliver good electrochemical performance with discharge capacities of 156.7 mA h g⁻¹ at 0.1 C, and exhibit 138.0 mA h g⁻¹ after 100 cycles at 0.5 C, which is 95.3% of the initial discharge capacity.     

The use of soil gas as radon source in radon chambers

A procedure is described in which soil gas is utilized as an alternative to the ²²⁶Ra source for the supply of the radon gas required to fill a radon chamber where radon-measuring devices are calibrated. The procedure offers opportunities to vary the radon concentration within the chamber around an average value of about 500 Bq/m³, which is considered to be sufficient for calibrating indoor radon detectors. The procedure is simple and the radon source does not require radiation protection certification (for import and/or use), unlike the commercially produced standard radioactive (²²⁶Ra) sources.