Long-term determination of airborne radon progeny concentrations using LR 115 detectors and the effects of thoron

The 'proxy equilibrium factor' (F_p) method has been developed for long-term determination of airborne radon progeny concentrations using LR 115 solid-state nuclear track detectors. In this paper, the effects of ²²⁰Rn on the F_p method have been studied. The correction to the track density was related to a parameter α which was the ratio of the sum of activity concentrations of alpha-particle emitting radionuclides in the ²²⁰Rn decay chain to the activity concentration of ²²⁰Rn alone. Under commonly encountered circumstances, α could not be smaller than 2. An attempt was made to verify this using the exposure chamber at the National Institute of Radiological Sciences (NIRS), Chiba, Japan. A most interesting observation of α <2 for very high ²²⁰Rn concentrations and very low equilibrium factors for ²²⁰Rn in the exposure chambers was made. A possible explanation was the substantial deposition of ²¹⁶Po under the extreme conditions inside the exposure chambers. © The Author 2010. Published by Oxford University Press. All rights reserved.