085 741 SIZE DISTRIBUTION, EQUILIBRIUM RATIO AND UNATTACHED FRACTION OF RADON DECAY PRODUCTS UNDER TYPICAL INDOOR DOMESTIC CONDITIONS

In order to characterise the behaviour of radon decay products under domestic conditions, long-term measurements were carried out from May 1997 to April 1998 in a typical dwelling located in Brittany (France). In particular, the unattached fraction and equilibrium factor were continuously measured. Moreover, the size distributions of unattached and attached radon daughters were investigated by using specific instruments implemented in the laboratory. All these experiments were carried out under different typical aerosol conditions. The results evidenced the strong influence exerted by the characteristics (concentration, size) of ambient aerosol on these different parameters. Key words: radon daughters, unattached fraction, equilibrium factor, radon daughter size distribution INTRODUCTION Radon-222, a rare natural radioactive gas, is present at different concentrations in soils and building materials. After emanation, it gives birth to the following short-lived radon decay products: Po-218, Pb-214, Bi-214 and Po-214. Due to their high diffusity, these solid particles can, then, attach to other particles present in the ambient air. It is well known that inhalation of radon daughters is responsible for about 40% of the total radiation dose received by populations. Their effect on the health depends on their behavior in indoor atmosphere. One can consider two main groups of radioactive particles: the first one called "unattached fraction" of size within 0.5 and several nanometers, while the second one corresponds to radon decay products in a larger size mode (10 -1000 nm) characterizing the "attached fraction". Unattached fraction, equilibrium factor and size distribution are the main influent parameters involved in the lung-dose calculation. Within the framework of the European program RARAD (1996RARAD ( -1999, experiments were carried out in a dwelling situated in Brittany during one year. Unattached fraction and equilibrium factor were continuously measured under different aerosol conditions. Moreover, spot measurements of unattached and attached size distributions of radon daughters were also performed. MATERIAL AND METHODS Continuous measurements of unattached fraction and equilibrium factor In order to continuously measure the unattached fraction and equilibrium ratio, we developed an original device consisting of two parallel sampling lines: an annular diffusion channel (ADC) and an open filter. As a matter of fact the diffusional behavior of the ADC geometry has been studied by analytical computation 085 Radon in the Living Environment, 19-23 April 1999, Athens, Greece 742 detector (PIPS CAM 900). Thus, only attached particles are collected. On the other hand, the open filter being also equipped with an alpha detector collects all the particles. Total and attached activity concentrations were determined by alpha spectroscopy using the method of Size distribution of unattached an attached radon daughters A granular bed diffusion battery was built in order to determine the size distribution of unattached Po-218 and Pb-214. It was composed of five granular beds, filled with glass or stainless steel balls, and a reference channel in parallel. Cut-off diameters ranged within 0.85 to 4.8 nm. The particles which were not deposited in the granular beds were collected on the downstream filters. The SDI-2001 used to collect the attached radioactive aerosol consists of an Andersen impactor followed by five granular beds in parallel After sampling periods of 5 to 10 minutes, activity concentrations of Po-218, Pb-214 and Bi-214 were determined by gross alpha counting using a modified TELS method (Hartley and Hartley, 1989). Then, the kernel matrixes of our sampling devices and the activity on each filter being known, size distributions were retrieved using RESULTS Experimental conditions Throughout the year of experimentation temperature and hygrometry remained quite stable with respective values around 20°C and 50%. Particle concentration was measured using a CNC TSI 3025, whereas the particle size distribution was determined thanks to a CNC TSI 3022 associated to a diffusion battery TSI 3040. Without sources, particle concentration was systematically below 5 000 cm-3, which is low. The mean particle concentration was 1 200 cm-3. It was greatly increased and reached 1 000 000 cm-3 in the presence of aerosols sources such as cigar and cooking smokes, or burning candles and fumigating sticks. Radon activity concentration was measured by electroprecipitation of the Po218+and ranged between 240 and 2 800 Bq.m-3 with a mean value of 1 400 Bq.m-3. The ventilation rate was estimated to 0.25 h-1 according to the method described by Unattached fraction and equilibrium factor The results of unattached fraction and equilibrium factor measurements with the aged aerosol and various aerosol sources are summarized in Radon in the Living Environment, 19-23 April 1999, Athens, Greece 085 743 With aerosol sources, the unattached fraction became negligible, i.e. below 5%, whereas the equilibrium factor was highly increased and sometimes reached values around 0.75. No unattached Pb-214 and no unattached Bi-214 were found; there was, sometimes, unattached Po-218. The time variation of unattached fraction and equilibrium factor with cigar smoke and fumigating sticks is illustrated on Nanometer size distribution of Po-218 and Pb-214 The nanometer size distributions of Po-218 and Pb-214 were found unimodal. The diameters obtained for the Po-218 with EVE and Twomey methods ranged from 0.5 to 1.25 nm, whereas geometric standard deviation (GSD) varied between 1.2 and 1.4 and 1.15 and 1.3, respectively. The EVE and Twomey algorithms gave mean diameters of 0.8 and 0.95, respectively. A typical example of the nanometer Po-218 size distribution is presented on The results obtained for Pb-214 and Po-218 were comparable. As a matter of fact, the EVE algorithm gave diameters within 0.55 and 1.25 nm with a GSD between 1.2 and 1.35 whereas Twomey gave diameters in the range 0.55-1.5 nm with GSD between 1.15 and 1.4. A typical example of nanometer Pb-214 size distribution is displayed on Attached size distributions The attached size distributions of radon daughters were also investigated under different aerosol conditions. No difference was observed between the radon daughters, so only the results concerning the potential alpha energy concentration (PAEC) will be presented hereafter. With the aged aerosol, the attached size distribution was unimodal with an accumulation mode around 190 nm and a GSD of 1.64. As more than 70% of experiments gave results with accumulation mode between 180 and 200 nm, that is only a difference of 20 nm the aged aerosol could be considered as stable. The size distributions obtained with cigar smoke and fumigating sticks were also unimodal. With the former, accumulation mode diameters ranged from 200 to 260 nm with a mean diameter of 222 nm and a GSD of 1.6. With the latter, accumulation modes varied between 240 and 280 nm with a mean diameter of 255 nm and a GSD of 1.57. These results confirmed those previously obtained during an inter-comparison campaign carried out in the same dwelling Some changes were observed with cooking smoke and burning candles. The former produced either unimodal or bimodal distributions. When the distributions were unimodal, the accumulation modes were between 160 and 205 nm with a mean diameter of 195 nm and a GSD of 1.6. In 63% of the cases, bimodal distributions were retrieved. The nucleation mode was around 35 nm with a GSD of 1.76 and accounted for 11% of the attached activity. Eighty nine percent of the attached activity fell within an accumulation mode around 200 nm with a GSD of 1.72. 085 Radon in the Living Environment, 19-23 April 1999, Athens, Greece 744 CONCLUSION In order to characterize the radon decay products under typical living conditions measurements were carried out over one year. They provided us with good quality information on unattached fraction, equilibrium factor and radon daughters size distribution. We noticed that the nature, i.e. concentration, size, of ambient aerosol exerted an important influence on parameters such as unattached fraction, equilibrium factor and radon daughters size distribution. This study provided us with a large database useful for a better characterization of uncertainties in dose-exposure calculations. In the future, a more precise and better characterization of the charged fraction of radon aerosol will be required to get a better understanding of the different cluster modes mentioned in the literature. ACKNOWLEDGMENT

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Simulation des transferts de contamination par les gaz et les aérosols

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International audienceThis paper deals with the production of charged water droplets by ElectroHydroDynamic Atomisation (EHDA) of water, in air at atmospheric pressure, in a mode stabilised by a particular corona discharge regime. Indeed, impulse filamentary discharges developing in the gas around the liquid cone temporarily disrupt the EHD equilibrium leading to an unstable mode of EHDA with varying droplet properties (size and charge). The purpose of this paper is to show that a stable mode can be obtained by the control of the field divergence around the liquid, i.e. the electric field profile in the gas, leading to a continuous glow discharge without impulse filamentary discharge. Using observations, electrical measurements and droplets size characterisation, several spraying modes are depicted. We have demonstrated that the electrical discharge regime (continuous/impulse) induces the mode of EHDA (stable/unstable). The stability domains are defined versus liquid flow rate, conductivity, voltage for different nozzle diameters. Then, the properties of droplets (droplets diameter, spray current) produced within these modes are established as a function of the liquid flow rate, of the conductivity and of the glow current

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Évaluation du facteur de mise en suspension de contamination dans les installations nucléaires


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Ion current density profiles in negative corona gaps versus EHD confinements

International audienceThis paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode. © 2015 Elsevier B.V