[Fractal behavior of indoor radon variations]

Recently, a new mathematical theory has been developed which describes the non-linear dynamic and complex systems which are widely diffused in nature. In spite of great variability in the phenomenon appearances, so great as to seem chaotic, the phenomena are described by algorithms which are, at times, very simple; they are characterized by a parameter, the so-called fractal dimension, which is a fractional number. We employed this new theory to verify the fractal behavior of temporal variations of radon 222 concentration, as measured in a house at Angera (Italy), 1986-1987. With significant correlation, the experimental data show the statistics of the system not to be casual and Gaussian, but chaotic and persistent, with Hurst exponent approximately 0.77 and fractal dimension 1.23. If the fractality of radon phenomena is verified also in other systems, the implications will be consistent. Particularly, punctual time predictability of radon concentration would no longer be possible, but a new prevision strategy would be necessary, considering the chaotic behavior of the phenomenon. This would imply, e.g., a new scientific approach both in planning surveys on the doses absorbed by people exposed to radon and in predicting seismic and volcanic phenomena, where radon is known to be a primary precursors of these catastrophic events.