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Microbeam facilities provide a unique opportunity to investigate the effects of ionising radiation on living biological cells with a precise control of the delivered dose. This paper describes dosimetry calculations performed at the single-cell level in the microbeam irradiation facility available at the Centre d'Etudes Nucléaires de Bordeaux-Cradignan in France, using (he object-oriented Geant4 Monte Carlo simulation toolkit. The cell geometry model is based on high-resolution three-dimensional voxelised phantoms of a human keratinocyte (HaCaT) cell line. Such phantoms are built from confocal microscopy imaging and from ion beam chemical elemental analysis. Results are presented for single-cell irradiation with 3 MeV incident alpha particles. [ABSTRACT FROM AUTHOR]

210Po and 210Pb represent the most abundant part of atmospheric aerosol long-lived natural radioactivity. Moreover, 210Pb-210Po monitoring in the atmosphere can be of interest for tracking extreme natural events that can enhance the level of alpha/beta radioactivity in air. In this paper, we question the possibility to use routine gross alpha/beta measurements in order to monitor 210Po, 210Pb and 210Po/210Pb ratio in the atmosphere. Based on joint gross alpha/beta measurement and 210Pb-210Po specific determination on 16 atmosphere samples, we show that (i) gross beta activity systematically overestimates 210Pb activity due to the presence of interfering beta emitters and (ii) gross alpha activity mostly reflects 210Po activity even if an underestimation is always observed due to alpha particle attenuation in the sample. In order to determine 210Po/210Pb ratio, we discuss the advantages of using gross alpha activity time variation compared to specific 210Po measurements. Finally, the gross alpha/beta ratio appear to be a good proxy of the 210Po/210Pb ratio when large-scale variations are to be monitored. We report a first reference level for the activity level of airborne 210Po in France of 13 ± 6 μBq/m3. • Joint analysis of 210Po, 210Pb and gross alpha/beta activities in 16 atmospheric samples. • Gross beta activity in atmospheric aerosols overestimates 210Pb activity because of interfering beta emitters. • Gross alpha/beta activity ratio tend to underestimate 210Po/210Pb activity ratio. • Large variations of 210Po/210Pb ratio could be monitored with gross alpha/beta activities. • Activity level of airborne 210Po in France of 13 ± 6 μBq/m3. [ABSTRACT FROM AUTHOR]