Correcting for H2O interference using a RAD7 electrostatic collection-based silicon detector

The effect of water molecules on the electrostatic collection of 218Po ions onto the surface of silicon detectors (neutralization) is evaluated through the comparison with a scintillation cell (ZnS), not affected by air humidity. A radon monitor (RAD7, Durridge Company) was connected to a stainless steel radon chamber, equipped with the scintillation cell. Radon gas, extracted from an acidified RaCl2 source, was injected into the chamber and the amount of water molecules in the system was alternatively lowered or increased (from 0.00075 to 0.014 g of water in RAD7) by connecting the chamber to a desiccant or to a bubbling water bottle. The relative efficiency of the silicon detector with respect to the scintillation cell decreases with the growth of water molecules inside RAD7. This dependence, with a fixed i) electrostatic chamber geometry and ii) nominal high voltage, diverges during the humidification or the drying phase because it is in turn influenced by the length of interaction of polonium atoms with water molecules, which impacts on the size of 218Po clusters and thus on the neutralization process. For water contents higher that 0.01 g in RAD7, this effect is greatly enhanced. Temperature in the investigated range (18.5-35.6 °C) does not affect the efficiency of electrostatic collection-based silicon detectors. Based on these experiments, admitting a certain error on the efficiency (from 1.8 to 7.5%, depending on the water content), proper corrections were developed to adjust soil radon readings, when a desiccant is removed. This operation is necessary if recent Non-Aqueous Phase Liquids (NAPLs) leakage has occurred in the subsoil to avoid the sorption and possible later release of radon by Drierite, with related partition between the solid and liquid phases (water and NAPL).

Cable, J.E., Burnett, W.C., Chanton, J.P., Weatherly, G.L., 1996. Estimating groundwater discharge into the northeastern Gulf of Mexico using radon-222. Earth Planet. Sci. Lett. 144, 591-604.
Chao, C.Y.H., Tung, T.C.W., Chan, D.W.T., Burnett, J., 1997. Determination of radon emanation and back diffusion characteristics of building materials in small chamber tests. Build. Environ. 32, 355-362.
Chu, K.-D., Hopke, P.K., 1988. Neutralization kinetics for polonium-218. Envir. Sci. Tech. 22, 711-717.
Cook, P.J., Favreau, G., Dighton, J.C., Tickell, S., 2003. Determining natural groundwater influx to a tropical river using radon, chlorofluorocarbons and ionic environmental tracers. J. Hydrol. 277, 74-88.
Corbett, D.R., Burnett, W.C., Cable, P.H., Clark, S.B., 1997. Radon tracing ofgroundwater input into par pond, Savannah river site. J. Hydrol. 203, 209-227.
Cuculeanu, V., Lupu, A., 2001. Deterministic chaos in atmospheric radon dynamics. Deterministic chaos in atmospheric radon dynamics. J. Geophys. Res. Atmos. 106, 961-968.
De Martino, S., Sabbarese, C., Monetti, G., 1998. Radon emanation and exhalation rates form soils measured with an electrostatic collector. Appl. Radiat. Isot. 49, 407-413.
De Simone, G., Galli, G., Lucchetti, C., Tuccimei, P., 2015a. Using natural radon as a tracer of gasoline contamination. P. Earth Planet. Sci. 13, 104-107, 11th Applied Isotope Geochemistry Conference, AIG-11 BRGM.
De Simone, G., Galli, G., Lucchetti, C., Tuccimei, P., 2015b. Calibration of BIG Bottle RAD H2O set-up for radon in water using HDPE bottles. Radiat. Meas. 76, 1-7.
Durridge, 2009. RAD7 Radon Detector User Manual.
(EPA) Environmental Protection Agency, 2003. EPA Assessment of Risks from Radon in Homes. 402-R-03-003. U.S. Environmental Protection Agency, Washington, DC.
Gatley, D.P., 2013. Understanding Psychrometrics, third ed. ASHRAE, Atlanta (GA), USA. ISBN 978-1-936504-31-2.
Guantario, C., 1997. Influenza dell’umidità sulla efficienza di rivelazione di radon mediante rivelatore allo stato solido. Tesi di Laurea in Ingegneria Nucleare. Università “La Sapienza”, Roma, Italy.
Hopke, P.K., 1989. Use of electrostatic collection of 218Po for measuring Rn. Health Phys. 57, 39-42.
Lucchetti, C., De Simone, G., Galli, G., Tuccimei, P., 2016. Evaluating radon loss from water during storage in standard PET, bio-based PET and PLA bottles. Radiat. Meas. 84, 1-8.
Mesbah, B., Fitzgerald, B., Hopke, P.K., Pourprix, M., 1997. New technique to measure the mobility size of ultrafine radioactive particles. Aerosol Sci. Tech. 27, 381-393.
Quindos, L.S., Sainz, C., Fuente, I., Gutierrez, J.L., Gonzalez, A., 2013. The use of radon as tracer in environmental sciences. Acta Geophys. 61, 848-858.
Roca, V., De Felice, P., Esposito, A.M., Pugliese, M., Sabbarese, C., Vaupotich, J., 2004. The influence of environmental parameters in electrostatic cell radon monitor response. Appl. Radiat. Isot. 61, 243-247.
Scarlato, P., Tuccimei, P., Mollo, S., Soligo, M., Castelluccio, M., 2013. Contrasting radon background levels in volcanic settings: clues from 220Rn activity concentrations measured during long-term deformation experiments. B. Volcanol. 75, 751. http://dx.doi.org/10.1007/s00445-013-0751-0.
Schubert, M., Freyer, K., Treutler, H.C.,Weiss, H., 2002. Using radon-222 in soil gas as an indicator of subsurface contamination by non-aqueous phase liquids (NAPLs). Geofis. Int. 41, 433-437.
Schubert, M., 2015. Using radon as environmental tracer for the assessment of subsurface non-aqueous phase liquid (NAPL) contamination e a review. Eur. Phys. J. Spec. Top. 224, 717-730.
Semprini, L., Hopkins, O.S., Tasker, B.R., 2000. Laboratory, field, and modeling studies of Radon-222 as a natural tracer for monitoring NAPL contamination. Transp. Porous Med. 38, 223-240.
Tuccimei, P., Moroni, M., Norcia, D., 2006. Simultaneous determination of 222Rn and 220Rn exhalation rates from building materials used in central Italy with accumulation chambers and a continuous solid state alpha detector: influence of particle size, humidity and precursors concentration. Appl. Radiat. Isot. 64, 254-263.
Tuccimei, P., Mollo, S., Vinciguerra, S., Castelluccio, M., Soligo, M., 2010. Radon and thoron emission from lithophysae-rich tuff under increasing deformation: an experimental study. Geophys. Res. Lett. 37, L05406. http://dx.doi.org/10.1029/2009GL041652, 12 March 2010.