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2 2010

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Radon decay products in the boundary layer of the atmosphere

Otahal P., Burian I.

Nukleonika

2010

Vol. 55, No. 4

539-542

The concentration of radon and its decay products in the boundary layer of the atmosphere varies and depends on many factors. One of the main factors leading to the variability of equilibrium equivalent concentration (EEC) of radon is the dynamic behavior of the atmosphere. Describing the behavior of radon concentration and EEC in the atmosphere is important for the estimation of natural human exposition (this was our original goal). The National Institute for Nuclear, Chemical and Biological Protection (SÚJCHBO, v.v.i.) has been investigating the characteristics of radon decay products in the boundary layer of the atmosphere since 1985. The measurements of EEC were carried out in places with different exhalation of radon from the subsoil. The grab sampling method, as well as continuous measurement, were applied in various areas. The determination of outdoor radon and radon daughter product (RnDP) is not easy due to very low levels of their concentrations: therefore, many methods and devices had to be modified for this type of measurement.

Filtration approach to mitigate indoor thoron progeny concentration

Wang J., Meisenberg O., Chen Y., Karg E., Tschiersch J.

Nukleonika

2010

Vol. 55, No. 4

445-450

This study investigates filtration of air as potential mitigation method of thoron progeny exposure. The experiments were conducted in a model room (volume 7.1 m3) which was equipped with a pump and an HEPA (high efficiency particulate air) filter. Filtration at a rate of 0.2, 0.4, 0.5 and 0.8 h–1 during 88 h proved an effective practice in reducing the total indoor thoron decay product concentration. The results indicate that 0.4–0.8 h–1 filtration rate had almost the same filtration efficiency in decreasing the total thoron EEC (equilibrium equivalent concentration) by 97 per cent while 80 per cent of total thoron EEC were reduced by 0.2 h–1 filtration rate; meanwhile, the unattached thoron EEC rose significantly by 190, 270, 290 per cent, respectively under 0.4–0.8 h–1 filtration rate, whereas 0.2 h–1 filtration rate increased unattached thoron EEC by 40 per cent. The aerosol number size distribution variation reveals that filtration operation removes smaller particles faster or earlier than the larger ones. The annual effective dose calculated was reduced by 91–92 per cent at a filtration rate of 0.4–0.8 h–1 while 75 per cent reduced at 0.2 h–1 filtration rate after 88 h filtration process.