Radiation Measurements 40 (2005) 657–661 www.elsevier.com/locate/radmeas Radonprogenydistributionsinsideadiffusionchamberandtheir contributionstotrackdensityinSSNTdetectors D. Palacios ∗ , L. Sajo-Bohus, E.D. Greaves Universidad Simon Bolivar, P.O. 89000, Caracas 1080-A,Venezuela Received 27 August 2004; received in revised form 1 June 2005; accepted 20 June 2005 Abstract Diffusion of alpha emitter radon progeny inside a cylindrical diffusion chamber was simulated. In the simulation of atomic movements, we took into account the random nature of the diffusion direction and the decay process. The alpha emitter distributions in volume, lateral wall and top cover of a 6.0cm height diffusion chamber for different diameters were determined. Results show non-uniform distribution of radon progeny. As chamber diameter increases, the tendency of radon progeny is to accumulate in central regions of the chamber volume ( 218 Po) and inner wall ( 218 Po and 214 Po). Depending on chamber diameter and detector size, non-uniform distribution of radon progeny deposited on SSNTs surface can be achieved if the detector is horizontally located at the bottom. The fraction of surface where 222 Rn progeny are deposited diminishes as chamber diameter increases. Due to the relatively short 218 Po half-life, for diameters larger than the assumed height its subsequent atoms decay in air before their deposition on chamber wall. The form in which radon progeny is distributed in volume and walls of chamber can affect the quantity and distribution of tracks in detector. © 2005 Elsevier Ltd. All rights reserved. Keywords: Radon progeny; Plate-out; Diffusion; Simulation 1. Introduction The problem of radon progeny deposition inside diffusion chambers has been focused mainly on the partitioning of 218 Po between the air volume and chamber wall. Theoreti- cal study on 218 Po deposition developed by McLaughlin and Fitzgerald (1994) revealed that 218 Po was almost completely deposited before decay, while Pressyanov et al. (1999) de- termined that deposition fraction of 218 Po atoms depends on the diameter and height of the cylindrical chamber. Nev- ertheless, as Nikezi´ c andYu (2004) outlined, the question of ∗ Corresponding author. Fax: +582129063590. E-mail address: palacios@usb.ve (D. Palacios). 1350-4487/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2005.06.017 uniformity or non-uniformity of deposition of radon progeny inside the chamber has not been tackled yet, neither exper- imentally nor theoretically. When diffusion chambers with SSNTD are used to mea- sure radon concentration in a given environment, it should be kept in mind that due to the plate-out process, the spatial distribution of radon progeny in air and walls of the cham- ber should not be uniform. However, most studies about radon progeny behaviour in diffusion chambers assumed their uniform distribution (Nikezi´ c and Yu, 2000; Bagnoli et al., 2001; Sima, 2001; Eappen and Mayya, 2004). This work has an objective to develop a method to simulate the diffusion process, plate-out and decay of radon progeny in- side a diffusion chamber in order to qualitatively analyze its distribution in volume and walls, in dependence of cham- ber diameter and how this can influence on induced track density.