Low dimensional chaos is present in radon time variations

An indoor radon (222Rn) concentration time series registered in a house at Angera (Italy) in 1986 and 1987 was characterised by an important aperiodic component presenting a chaotic-deterministic behaviour. The data were analysed by comparing three algorithms that are used to extract phase-space dynamical information from experimental time series. They show different fractal dimensions. Consequently, the phenomenon is intrinsically unpredictable and a small number of parameters (related to fractal dimension) can be sufficient to describe its attractor dynamics, even when it is influenced by many variables such as micro climatic and geological conditions. Also large, rare concentrations, related to small changes in the above mentioned variables are present in radon time sets.