Explicit finite difference solution of the diffusion equation describing the flow of radon through soil

Applied Radiation and Isotopes 69 (2011) 237–240

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Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso

Explicit finite difference solution of the diffusion equation describing the flow of radon through soil
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Svetislav Savovic a,b,n, Alexandar Djordjevich a, Peter W. Tse a, Dragoslav Nikezic b a b

City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong, China
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Faculty of Science, R. Domanovica 12, 34000 Kragujevac, Serbia

a r t i c l e in fo

abstract

Article history:
Received 13 April 2010
Received in revised form
13 September 2010
Accepted 14 September 2010

Radon diffusion through soil and into air is investigated. The solution of the relevant diffusion equation is given using the explicit finite difference method. Results from a two-medium model (soil–air) are compared to those from a simplified single-medium model (soil alone). The latter are an underestimate in early stages of the diffusion process. Later on, the two models match closely and either one can be used at equilibrium conditions to calculate radon diffusion, estimate indoor radon concentration and assess health hazards.
& 2010 Elsevier Ltd. All rights reserved.

Keywords:
Radon
Diffusion equation
Finite difference method
Soil

1. Introduction
The radioactive gas radon (whose principal isotope is 222Rn) has been studied extensively over the past few decades.
Important motivating factors for this interest are the hazards associated with radon and its use as an environmental tracer
(Escobar et al., 1999). In a built environment, radon originates primarily from soil. Building material and some utility supply
(water and gas) contribute as well. It was reported that a worldwide average of 60.4 percent of total indoor radon originates from the ground under and surrounding buildings
(Ren, 2001). Its entry indoor is chiefly by diffusion through cracks in the building

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