Multifractal detrended cross-correlation analysis of radioactivity borne radon, thoron and meteorological time series

Abstract

Owing to the potential health threats due to sustained exposure from the radioactivity born radon and thoron gases and their applications, especially radon as earthquake precursor, the complex dynamic relationship between either of the radioactive gas with meteorological parameters has become the focus of research area. Several studies have reported that meteorological factors greatly influence the radon and thoron radioactive gases. In present study we investigated the scaling behavior of cross-correlations between simultaneously observed Radon and Thoron time series with temperature, pressure, and humidity time series. Data for radon, thoron and other meteorological parameters were obtained using RTM 1688-2 active detector from March 2017 to April 2018, with the total number of data points in each time series greater then fifteen thousands. Data obtained was investigated by Multi-fractal Detrended Cross-correlation Analysis (MFDXA) method through detrended covariance function. The computed cross-correlations were also investigated for multifractal or monofractal nature as well as for the degree of multifractality. Results of the study show that all correlations exhibit long range power law behavior. A nonlinear variation of scaling exponent ′hxy(q)′ vs ‘q’ (order of fluctuation) shows multifractal nature of cross-correlations with hxy(q)>0.5 for all correlations. Which means that all correlations are persistently positive correlated. The degree of multifractality was estimated by the width of singularity spectrum Δα. The results show that for each of the correlations width of singularity spectrum is nonzero confirming the multifractal nature of computed correlations. Finally, for Radon/Thoron correlation with temperature and humidity the width of singularity spectrum i.e., Δα>0.5 shows high multifractality when compared with Radon/Thoron vs pressure correlation with Δα<0.5 showing low multifractality.