Major parameters affecting the calculation of equilibrium factor using SSNTD-measured track densities
Introduction
The hazard of inhaling radon comes from its radioactive decay products which get trapped in the lung depositing their -particles energy in the tissue. Disintegration, ventilation and deposition (plate-out) are considered as the removal processes which reduce the activity of radon and its daughters in air lower than the equilibrium value. The equilibrium factor was introduced to simulate this situation and consider a very important parameter to calculate the effective dose from radon and its daughters (Faj and Planinić, 1991).
Solid state nuclear track detectors (SSNTD) become the state-of-the-art nuclear track detector for long-term radon measurements. These detectors can be exposed to radon and/or radon daughters by different configurations (Nikolaev and Ilic`, 1999). The basic configurations are the can-mode and bare-mode configurations. In can-mode configuration, the detector was equipped in the lower part of a cup covered with semi-permeable membrane. The membrane has a role to let radon only entering the cup and prevents thoron, radon daughters and dust. In bare-mode configurations (bare track detector), the detector was exposed freely to radon as well as radon daughters.
The equilibrium factor was determined by SSNTD based on using can and bare method. In this method, two similar detectors were exposed to radon, one in can-mode configuration (in can detector) and the other in bare-mode configuration (bare detector). can be found as a function of the track density ratio between bare and in can detector, respectively. The problem of finding this function was solved by Planinic’ et al. (Planinic` and Faj, 1989; Faj and Planinić, 1991) using mathematical solution based on solving the equation of as a function of the ventilation rate with together using a Cardon's formula and RND computer program to get as a function of . This solution was based on the assumptions that the two detectors have the same calibration factor (or response) for radon and registered alpha particles from radon and its daughters by the same efficiency.
Section snippets
Graphical solution of
The equilibrium factor is strongly dependent on the ventilation rate ; this dependence was expressed as (Planinic` and Faj, 1990)where, and are the decay constant of Po , Pb , Bi , respectively.
The track density of both bare and in can detector relates the concentration of radon and its daughters as where is the detector response. , and are the
Theoretical approaches
The above-mentioned solutions (approximate graphical and Planinic’ solution) have no comment on the used detector type (different detectors are different in response, registration energy window, critical angle, etc.) or the diffusion chamber (the cups are different in dimensions and has permeable membrane). Also, these solutions did not deal with the behavior of alpha emitters around the detectors. The above parameters were discussed in this work.
Results and discussion
The listed parameters in Table 1 were introduced into Eq. (7) and substituting the values of as a function of (the ventilation rate) to simply get as a function of . Substituting ranged from 0 to with 0.01 intervals into (Eq. (7)) and (Eq. (1)). Therefore, for each one can get and which can be plotted together as shown in Fig. 2 for CR-39 equipped in Terradex cup (curve 2) and in our cup (curve 3) and compared with the approximate solution (curve
Conclusion
The equilibrium factor as a function of was solved graphically and shows a good agreement with the mathematical solution given elsewhere. The simplicity of graphical solution makes us introduce all parameters that affects the equilibrium factor.
This study dealt with two widely different detectors equipped in two widely different diffusion cups. Any diffusion chamber covered with polyethylene membrane has results located within the range of our study. Future work is directed to generalize
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