Equilibrium factor determination using SSNTDs

The proxy equilibrium factor Fp was recently proposed by Nikezic et al. [2004. Theoretical basis for long-term measurements of equilibrium factor using LR 115 detector. Appl. Radiat. Isot. 61, 1431-1435] and Yu et al. [2005. Long-term measurements of radon progeny concentrations with solid state nuclear track detectors. Radiat. Meas. 40, 560-568] for long-term passive monitoring of the equilibrium factor F for short-lived 222Rn progeny. In the present paper, we further look into the details for the Fp method and study the potential factors affecting the measurements of F using this technique. These factors include (1) the removed active layer of the LR 115 detector, (2) the presence of 220Rn in the ambient environment, and (3) the deposition of dust particles on the LR 115 detector. The corresponding results are: (1) the removed active layer thickness of the LR 115 detector is a very critical parameter in determining Fp and hence F; (2) the presence of thoron in the ambient environment will affect the track densities on the bare LR 115 detector but can be corrected for using the partial sensitivities to thoron; and (3) deposition of dust particles on the bare LR 115 detectors normally will not have significant effects. In addition, a mini-survey of radon and thoron gas concentration and the radon equilibrium factor in different indoor environments has been carried out in different seasons. The conclusion is that the use of an assumed constant F value can result in inaccurate determinations of the effective dose; therefore, actual (long-term) measurements of the F values should be made.